d5702162f8
Having snd_BUG_ON() only evaluate its conditional when CONFIG_SND_DEBUG is set leads to frequent bugs, since other similar macros in the kernel have different behavior. Let's make snd_BUG_ON() act like those macros so it will stop being accidentally misused. Signed-off-by: Christine Spang <christine.spang@oracle.com> Signed-off-by: Takashi Iwai <tiwai@suse.de>
6198 lines
199 KiB
XML
6198 lines
199 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
|
|
|
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<!-- ****************************************************** -->
|
|
<!-- Header -->
|
|
<!-- ****************************************************** -->
|
|
<book id="Writing-an-ALSA-Driver">
|
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<bookinfo>
|
|
<title>Writing an ALSA Driver</title>
|
|
<author>
|
|
<firstname>Takashi</firstname>
|
|
<surname>Iwai</surname>
|
|
<affiliation>
|
|
<address>
|
|
<email>tiwai@suse.de</email>
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</address>
|
|
</affiliation>
|
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</author>
|
|
|
|
<date>Oct 15, 2007</date>
|
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<edition>0.3.7</edition>
|
|
|
|
<abstract>
|
|
<para>
|
|
This document describes how to write an ALSA (Advanced Linux
|
|
Sound Architecture) driver.
|
|
</para>
|
|
</abstract>
|
|
|
|
<legalnotice>
|
|
<para>
|
|
Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email>
|
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</para>
|
|
|
|
<para>
|
|
This document is free; you can redistribute it and/or modify it
|
|
under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2 of the License, or
|
|
(at your option) any later version.
|
|
</para>
|
|
|
|
<para>
|
|
This document is distributed in the hope that it will be useful,
|
|
but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the
|
|
implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A
|
|
PARTICULAR PURPOSE</emphasis>. See the GNU General Public License
|
|
for more details.
|
|
</para>
|
|
|
|
<para>
|
|
You should have received a copy of the GNU General Public
|
|
License along with this program; if not, write to the Free
|
|
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
|
|
MA 02111-1307 USA
|
|
</para>
|
|
</legalnotice>
|
|
|
|
</bookinfo>
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Preface -->
|
|
<!-- ****************************************************** -->
|
|
<preface id="preface">
|
|
<title>Preface</title>
|
|
<para>
|
|
This document describes how to write an
|
|
<ulink url="http://www.alsa-project.org/"><citetitle>
|
|
ALSA (Advanced Linux Sound Architecture)</citetitle></ulink>
|
|
driver. The document focuses mainly on PCI soundcards.
|
|
In the case of other device types, the API might
|
|
be different, too. However, at least the ALSA kernel API is
|
|
consistent, and therefore it would be still a bit help for
|
|
writing them.
|
|
</para>
|
|
|
|
<para>
|
|
This document targets people who already have enough
|
|
C language skills and have basic linux kernel programming
|
|
knowledge. This document doesn't explain the general
|
|
topic of linux kernel coding and doesn't cover low-level
|
|
driver implementation details. It only describes
|
|
the standard way to write a PCI sound driver on ALSA.
|
|
</para>
|
|
|
|
<para>
|
|
If you are already familiar with the older ALSA ver.0.5.x API, you
|
|
can check the drivers such as <filename>sound/pci/es1938.c</filename> or
|
|
<filename>sound/pci/maestro3.c</filename> which have also almost the same
|
|
code-base in the ALSA 0.5.x tree, so you can compare the differences.
|
|
</para>
|
|
|
|
<para>
|
|
This document is still a draft version. Any feedback and
|
|
corrections, please!!
|
|
</para>
|
|
</preface>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- File Tree Structure -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="file-tree">
|
|
<title>File Tree Structure</title>
|
|
|
|
<section id="file-tree-general">
|
|
<title>General</title>
|
|
<para>
|
|
The ALSA drivers are provided in two ways.
|
|
</para>
|
|
|
|
<para>
|
|
One is the trees provided as a tarball or via cvs from the
|
|
ALSA's ftp site, and another is the 2.6 (or later) Linux kernel
|
|
tree. To synchronize both, the ALSA driver tree is split into
|
|
two different trees: alsa-kernel and alsa-driver. The former
|
|
contains purely the source code for the Linux 2.6 (or later)
|
|
tree. This tree is designed only for compilation on 2.6 or
|
|
later environment. The latter, alsa-driver, contains many subtle
|
|
files for compiling ALSA drivers outside of the Linux kernel tree,
|
|
wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API,
|
|
and additional drivers which are still in development or in
|
|
tests. The drivers in alsa-driver tree will be moved to
|
|
alsa-kernel (and eventually to the 2.6 kernel tree) when they are
|
|
finished and confirmed to work fine.
|
|
</para>
|
|
|
|
<para>
|
|
The file tree structure of ALSA driver is depicted below. Both
|
|
alsa-kernel and alsa-driver have almost the same file
|
|
structure, except for <quote>core</quote> directory. It's
|
|
named as <quote>acore</quote> in alsa-driver tree.
|
|
|
|
<example>
|
|
<title>ALSA File Tree Structure</title>
|
|
<literallayout>
|
|
sound
|
|
/core
|
|
/oss
|
|
/seq
|
|
/oss
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|
/instr
|
|
/ioctl32
|
|
/include
|
|
/drivers
|
|
/mpu401
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|
/opl3
|
|
/i2c
|
|
/l3
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|
/synth
|
|
/emux
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|
/pci
|
|
/(cards)
|
|
/isa
|
|
/(cards)
|
|
/arm
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|
/ppc
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|
/sparc
|
|
/usb
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/pcmcia /(cards)
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|
/oss
|
|
</literallayout>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-core-directory">
|
|
<title>core directory</title>
|
|
<para>
|
|
This directory contains the middle layer which is the heart
|
|
of ALSA drivers. In this directory, the native ALSA modules are
|
|
stored. The sub-directories contain different modules and are
|
|
dependent upon the kernel config.
|
|
</para>
|
|
|
|
<section id="file-tree-core-directory-oss">
|
|
<title>core/oss</title>
|
|
|
|
<para>
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|
The codes for PCM and mixer OSS emulation modules are stored
|
|
in this directory. The rawmidi OSS emulation is included in
|
|
the ALSA rawmidi code since it's quite small. The sequencer
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|
code is stored in <filename>core/seq/oss</filename> directory (see
|
|
<link linkend="file-tree-core-directory-seq-oss"><citetitle>
|
|
below</citetitle></link>).
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-core-directory-ioctl32">
|
|
<title>core/ioctl32</title>
|
|
|
|
<para>
|
|
This directory contains the 32bit-ioctl wrappers for 64bit
|
|
architectures such like x86-64, ppc64 and sparc64. For 32bit
|
|
and alpha architectures, these are not compiled.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-core-directory-seq">
|
|
<title>core/seq</title>
|
|
<para>
|
|
This directory and its sub-directories are for the ALSA
|
|
sequencer. This directory contains the sequencer core and
|
|
primary sequencer modules such like snd-seq-midi,
|
|
snd-seq-virmidi, etc. They are compiled only when
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|
<constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel
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config.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-core-directory-seq-oss">
|
|
<title>core/seq/oss</title>
|
|
<para>
|
|
This contains the OSS sequencer emulation codes.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-core-directory-deq-instr">
|
|
<title>core/seq/instr</title>
|
|
<para>
|
|
This directory contains the modules for the sequencer
|
|
instrument layer.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="file-tree-include-directory">
|
|
<title>include directory</title>
|
|
<para>
|
|
This is the place for the public header files of ALSA drivers,
|
|
which are to be exported to user-space, or included by
|
|
several files at different directories. Basically, the private
|
|
header files should not be placed in this directory, but you may
|
|
still find files there, due to historical reasons :)
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-drivers-directory">
|
|
<title>drivers directory</title>
|
|
<para>
|
|
This directory contains code shared among different drivers
|
|
on different architectures. They are hence supposed not to be
|
|
architecture-specific.
|
|
For example, the dummy pcm driver and the serial MIDI
|
|
driver are found in this directory. In the sub-directories,
|
|
there is code for components which are independent from
|
|
bus and cpu architectures.
|
|
</para>
|
|
|
|
<section id="file-tree-drivers-directory-mpu401">
|
|
<title>drivers/mpu401</title>
|
|
<para>
|
|
The MPU401 and MPU401-UART modules are stored here.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-drivers-directory-opl3">
|
|
<title>drivers/opl3 and opl4</title>
|
|
<para>
|
|
The OPL3 and OPL4 FM-synth stuff is found here.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="file-tree-i2c-directory">
|
|
<title>i2c directory</title>
|
|
<para>
|
|
This contains the ALSA i2c components.
|
|
</para>
|
|
|
|
<para>
|
|
Although there is a standard i2c layer on Linux, ALSA has its
|
|
own i2c code for some cards, because the soundcard needs only a
|
|
simple operation and the standard i2c API is too complicated for
|
|
such a purpose.
|
|
</para>
|
|
|
|
<section id="file-tree-i2c-directory-l3">
|
|
<title>i2c/l3</title>
|
|
<para>
|
|
This is a sub-directory for ARM L3 i2c.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="file-tree-synth-directory">
|
|
<title>synth directory</title>
|
|
<para>
|
|
This contains the synth middle-level modules.
|
|
</para>
|
|
|
|
<para>
|
|
So far, there is only Emu8000/Emu10k1 synth driver under
|
|
the <filename>synth/emux</filename> sub-directory.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-pci-directory">
|
|
<title>pci directory</title>
|
|
<para>
|
|
This directory and its sub-directories hold the top-level card modules
|
|
for PCI soundcards and the code specific to the PCI BUS.
|
|
</para>
|
|
|
|
<para>
|
|
The drivers compiled from a single file are stored directly
|
|
in the pci directory, while the drivers with several source files are
|
|
stored on their own sub-directory (e.g. emu10k1, ice1712).
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-isa-directory">
|
|
<title>isa directory</title>
|
|
<para>
|
|
This directory and its sub-directories hold the top-level card modules
|
|
for ISA soundcards.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-arm-ppc-sparc-directories">
|
|
<title>arm, ppc, and sparc directories</title>
|
|
<para>
|
|
They are used for top-level card modules which are
|
|
specific to one of these architectures.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-usb-directory">
|
|
<title>usb directory</title>
|
|
<para>
|
|
This directory contains the USB-audio driver. In the latest version, the
|
|
USB MIDI driver is integrated in the usb-audio driver.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-pcmcia-directory">
|
|
<title>pcmcia directory</title>
|
|
<para>
|
|
The PCMCIA, especially PCCard drivers will go here. CardBus
|
|
drivers will be in the pci directory, because their API is identical
|
|
to that of standard PCI cards.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="file-tree-oss-directory">
|
|
<title>oss directory</title>
|
|
<para>
|
|
The OSS/Lite source files are stored here in Linux 2.6 (or
|
|
later) tree. In the ALSA driver tarball, this directory is empty,
|
|
of course :)
|
|
</para>
|
|
</section>
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Basic Flow for PCI Drivers -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="basic-flow">
|
|
<title>Basic Flow for PCI Drivers</title>
|
|
|
|
<section id="basic-flow-outline">
|
|
<title>Outline</title>
|
|
<para>
|
|
The minimum flow for PCI soundcards is as follows:
|
|
|
|
<itemizedlist>
|
|
<listitem><para>define the PCI ID table (see the section
|
|
<link linkend="pci-resource-entries"><citetitle>PCI Entries
|
|
</citetitle></link>).</para></listitem>
|
|
<listitem><para>create <function>probe()</function> callback.</para></listitem>
|
|
<listitem><para>create <function>remove()</function> callback.</para></listitem>
|
|
<listitem><para>create a <structname>pci_driver</structname> structure
|
|
containing the three pointers above.</para></listitem>
|
|
<listitem><para>create an <function>init()</function> function just calling
|
|
the <function>pci_register_driver()</function> to register the pci_driver table
|
|
defined above.</para></listitem>
|
|
<listitem><para>create an <function>exit()</function> function to call
|
|
the <function>pci_unregister_driver()</function> function.</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-example">
|
|
<title>Full Code Example</title>
|
|
<para>
|
|
The code example is shown below. Some parts are kept
|
|
unimplemented at this moment but will be filled in the
|
|
next sections. The numbers in the comment lines of the
|
|
<function>snd_mychip_probe()</function> function
|
|
refer to details explained in the following section.
|
|
|
|
<example>
|
|
<title>Basic Flow for PCI Drivers - Example</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#include <linux/init.h>
|
|
#include <linux/pci.h>
|
|
#include <linux/slab.h>
|
|
#include <sound/core.h>
|
|
#include <sound/initval.h>
|
|
|
|
/* module parameters (see "Module Parameters") */
|
|
/* SNDRV_CARDS: maximum number of cards supported by this module */
|
|
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
|
|
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
|
|
static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
|
|
|
|
/* definition of the chip-specific record */
|
|
struct mychip {
|
|
struct snd_card *card;
|
|
/* the rest of the implementation will be in section
|
|
* "PCI Resource Management"
|
|
*/
|
|
};
|
|
|
|
/* chip-specific destructor
|
|
* (see "PCI Resource Management")
|
|
*/
|
|
static int snd_mychip_free(struct mychip *chip)
|
|
{
|
|
.... /* will be implemented later... */
|
|
}
|
|
|
|
/* component-destructor
|
|
* (see "Management of Cards and Components")
|
|
*/
|
|
static int snd_mychip_dev_free(struct snd_device *device)
|
|
{
|
|
return snd_mychip_free(device->device_data);
|
|
}
|
|
|
|
/* chip-specific constructor
|
|
* (see "Management of Cards and Components")
|
|
*/
|
|
static int snd_mychip_create(struct snd_card *card,
|
|
struct pci_dev *pci,
|
|
struct mychip **rchip)
|
|
{
|
|
struct mychip *chip;
|
|
int err;
|
|
static struct snd_device_ops ops = {
|
|
.dev_free = snd_mychip_dev_free,
|
|
};
|
|
|
|
*rchip = NULL;
|
|
|
|
/* check PCI availability here
|
|
* (see "PCI Resource Management")
|
|
*/
|
|
....
|
|
|
|
/* allocate a chip-specific data with zero filled */
|
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL);
|
|
if (chip == NULL)
|
|
return -ENOMEM;
|
|
|
|
chip->card = card;
|
|
|
|
/* rest of initialization here; will be implemented
|
|
* later, see "PCI Resource Management"
|
|
*/
|
|
....
|
|
|
|
err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
|
|
if (err < 0) {
|
|
snd_mychip_free(chip);
|
|
return err;
|
|
}
|
|
|
|
snd_card_set_dev(card, &pci->dev);
|
|
|
|
*rchip = chip;
|
|
return 0;
|
|
}
|
|
|
|
/* constructor -- see "Constructor" sub-section */
|
|
static int snd_mychip_probe(struct pci_dev *pci,
|
|
const struct pci_device_id *pci_id)
|
|
{
|
|
static int dev;
|
|
struct snd_card *card;
|
|
struct mychip *chip;
|
|
int err;
|
|
|
|
/* (1) */
|
|
if (dev >= SNDRV_CARDS)
|
|
return -ENODEV;
|
|
if (!enable[dev]) {
|
|
dev++;
|
|
return -ENOENT;
|
|
}
|
|
|
|
/* (2) */
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
|
|
if (err < 0)
|
|
return err;
|
|
|
|
/* (3) */
|
|
err = snd_mychip_create(card, pci, &chip);
|
|
if (err < 0) {
|
|
snd_card_free(card);
|
|
return err;
|
|
}
|
|
|
|
/* (4) */
|
|
strcpy(card->driver, "My Chip");
|
|
strcpy(card->shortname, "My Own Chip 123");
|
|
sprintf(card->longname, "%s at 0x%lx irq %i",
|
|
card->shortname, chip->ioport, chip->irq);
|
|
|
|
/* (5) */
|
|
.... /* implemented later */
|
|
|
|
/* (6) */
|
|
err = snd_card_register(card);
|
|
if (err < 0) {
|
|
snd_card_free(card);
|
|
return err;
|
|
}
|
|
|
|
/* (7) */
|
|
pci_set_drvdata(pci, card);
|
|
dev++;
|
|
return 0;
|
|
}
|
|
|
|
/* destructor -- see the "Destructor" sub-section */
|
|
static void snd_mychip_remove(struct pci_dev *pci)
|
|
{
|
|
snd_card_free(pci_get_drvdata(pci));
|
|
pci_set_drvdata(pci, NULL);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor">
|
|
<title>Constructor</title>
|
|
<para>
|
|
The real constructor of PCI drivers is the <function>probe</function> callback.
|
|
The <function>probe</function> callback and other component-constructors which are called
|
|
from the <function>probe</function> callback cannot be used with
|
|
the <parameter>__init</parameter> prefix
|
|
because any PCI device could be a hotplug device.
|
|
</para>
|
|
|
|
<para>
|
|
In the <function>probe</function> callback, the following scheme is often used.
|
|
</para>
|
|
|
|
<section id="basic-flow-constructor-device-index">
|
|
<title>1) Check and increment the device index.</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int dev;
|
|
....
|
|
if (dev >= SNDRV_CARDS)
|
|
return -ENODEV;
|
|
if (!enable[dev]) {
|
|
dev++;
|
|
return -ENOENT;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where enable[dev] is the module option.
|
|
</para>
|
|
|
|
<para>
|
|
Each time the <function>probe</function> callback is called, check the
|
|
availability of the device. If not available, simply increment
|
|
the device index and returns. dev will be incremented also
|
|
later (<link
|
|
linkend="basic-flow-constructor-set-pci"><citetitle>step
|
|
7</citetitle></link>).
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-create-card">
|
|
<title>2) Create a card instance</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_card *card;
|
|
int err;
|
|
....
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The details will be explained in the section
|
|
<link linkend="card-management-card-instance"><citetitle>
|
|
Management of Cards and Components</citetitle></link>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-create-main">
|
|
<title>3) Create a main component</title>
|
|
<para>
|
|
In this part, the PCI resources are allocated.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip *chip;
|
|
....
|
|
err = snd_mychip_create(card, pci, &chip);
|
|
if (err < 0) {
|
|
snd_card_free(card);
|
|
return err;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
The details will be explained in the section <link
|
|
linkend="pci-resource"><citetitle>PCI Resource
|
|
Management</citetitle></link>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-main-component">
|
|
<title>4) Set the driver ID and name strings.</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
strcpy(card->driver, "My Chip");
|
|
strcpy(card->shortname, "My Own Chip 123");
|
|
sprintf(card->longname, "%s at 0x%lx irq %i",
|
|
card->shortname, chip->ioport, chip->irq);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
The driver field holds the minimal ID string of the
|
|
chip. This is used by alsa-lib's configurator, so keep it
|
|
simple but unique.
|
|
Even the same driver can have different driver IDs to
|
|
distinguish the functionality of each chip type.
|
|
</para>
|
|
|
|
<para>
|
|
The shortname field is a string shown as more verbose
|
|
name. The longname field contains the information
|
|
shown in <filename>/proc/asound/cards</filename>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-create-other">
|
|
<title>5) Create other components, such as mixer, MIDI, etc.</title>
|
|
<para>
|
|
Here you define the basic components such as
|
|
<link linkend="pcm-interface"><citetitle>PCM</citetitle></link>,
|
|
mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>),
|
|
MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>),
|
|
and other interfaces.
|
|
Also, if you want a <link linkend="proc-interface"><citetitle>proc
|
|
file</citetitle></link>, define it here, too.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-register-card">
|
|
<title>6) Register the card instance.</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
err = snd_card_register(card);
|
|
if (err < 0) {
|
|
snd_card_free(card);
|
|
return err;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Will be explained in the section <link
|
|
linkend="card-management-registration"><citetitle>Management
|
|
of Cards and Components</citetitle></link>, too.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-constructor-set-pci">
|
|
<title>7) Set the PCI driver data and return zero.</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
pci_set_drvdata(pci, card);
|
|
dev++;
|
|
return 0;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
In the above, the card record is stored. This pointer is
|
|
used in the remove callback and power-management
|
|
callbacks, too.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="basic-flow-destructor">
|
|
<title>Destructor</title>
|
|
<para>
|
|
The destructor, remove callback, simply releases the card
|
|
instance. Then the ALSA middle layer will release all the
|
|
attached components automatically.
|
|
</para>
|
|
|
|
<para>
|
|
It would be typically like the following:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void snd_mychip_remove(struct pci_dev *pci)
|
|
{
|
|
snd_card_free(pci_get_drvdata(pci));
|
|
pci_set_drvdata(pci, NULL);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
The above code assumes that the card pointer is set to the PCI
|
|
driver data.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="basic-flow-header-files">
|
|
<title>Header Files</title>
|
|
<para>
|
|
For the above example, at least the following include files
|
|
are necessary.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#include <linux/init.h>
|
|
#include <linux/pci.h>
|
|
#include <linux/slab.h>
|
|
#include <sound/core.h>
|
|
#include <sound/initval.h>
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where the last one is necessary only when module options are
|
|
defined in the source file. If the code is split into several
|
|
files, the files without module options don't need them.
|
|
</para>
|
|
|
|
<para>
|
|
In addition to these headers, you'll need
|
|
<filename><linux/interrupt.h></filename> for interrupt
|
|
handling, and <filename><asm/io.h></filename> for I/O
|
|
access. If you use the <function>mdelay()</function> or
|
|
<function>udelay()</function> functions, you'll need to include
|
|
<filename><linux/delay.h></filename> too.
|
|
</para>
|
|
|
|
<para>
|
|
The ALSA interfaces like the PCM and control APIs are defined in other
|
|
<filename><sound/xxx.h></filename> header files.
|
|
They have to be included after
|
|
<filename><sound/core.h></filename>.
|
|
</para>
|
|
|
|
</section>
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Management of Cards and Components -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="card-management">
|
|
<title>Management of Cards and Components</title>
|
|
|
|
<section id="card-management-card-instance">
|
|
<title>Card Instance</title>
|
|
<para>
|
|
For each soundcard, a <quote>card</quote> record must be allocated.
|
|
</para>
|
|
|
|
<para>
|
|
A card record is the headquarters of the soundcard. It manages
|
|
the whole list of devices (components) on the soundcard, such as
|
|
PCM, mixers, MIDI, synthesizer, and so on. Also, the card
|
|
record holds the ID and the name strings of the card, manages
|
|
the root of proc files, and controls the power-management states
|
|
and hotplug disconnections. The component list on the card
|
|
record is used to manage the correct release of resources at
|
|
destruction.
|
|
</para>
|
|
|
|
<para>
|
|
As mentioned above, to create a card instance, call
|
|
<function>snd_card_create()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_card *card;
|
|
int err;
|
|
err = snd_card_create(index, id, module, extra_size, &card);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The function takes five arguments, the card-index number, the
|
|
id string, the module pointer (usually
|
|
<constant>THIS_MODULE</constant>),
|
|
the size of extra-data space, and the pointer to return the
|
|
card instance. The extra_size argument is used to
|
|
allocate card->private_data for the
|
|
chip-specific data. Note that these data
|
|
are allocated by <function>snd_card_create()</function>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="card-management-component">
|
|
<title>Components</title>
|
|
<para>
|
|
After the card is created, you can attach the components
|
|
(devices) to the card instance. In an ALSA driver, a component is
|
|
represented as a struct <structname>snd_device</structname> object.
|
|
A component can be a PCM instance, a control interface, a raw
|
|
MIDI interface, etc. Each such instance has one component
|
|
entry.
|
|
</para>
|
|
|
|
<para>
|
|
A component can be created via
|
|
<function>snd_device_new()</function> function.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_device_new(card, SNDRV_DEV_XXX, chip, &ops);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
This takes the card pointer, the device-level
|
|
(<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the
|
|
callback pointers (<parameter>&ops</parameter>). The
|
|
device-level defines the type of components and the order of
|
|
registration and de-registration. For most components, the
|
|
device-level is already defined. For a user-defined component,
|
|
you can use <constant>SNDRV_DEV_LOWLEVEL</constant>.
|
|
</para>
|
|
|
|
<para>
|
|
This function itself doesn't allocate the data space. The data
|
|
must be allocated manually beforehand, and its pointer is passed
|
|
as the argument. This pointer (<parameter>chip</parameter> in the
|
|
above example) is used as the identifier for the instance.
|
|
</para>
|
|
|
|
<para>
|
|
Each pre-defined ALSA component such as ac97 and pcm calls
|
|
<function>snd_device_new()</function> inside its
|
|
constructor. The destructor for each component is defined in the
|
|
callback pointers. Hence, you don't need to take care of
|
|
calling a destructor for such a component.
|
|
</para>
|
|
|
|
<para>
|
|
If you wish to create your own component, you need to
|
|
set the destructor function to the dev_free callback in
|
|
the <parameter>ops</parameter>, so that it can be released
|
|
automatically via <function>snd_card_free()</function>.
|
|
The next example will show an implementation of chip-specific
|
|
data.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="card-management-chip-specific">
|
|
<title>Chip-Specific Data</title>
|
|
<para>
|
|
Chip-specific information, e.g. the I/O port address, its
|
|
resource pointer, or the irq number, is stored in the
|
|
chip-specific record.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
....
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
In general, there are two ways of allocating the chip record.
|
|
</para>
|
|
|
|
<section id="card-management-chip-specific-snd-card-new">
|
|
<title>1. Allocating via <function>snd_card_create()</function>.</title>
|
|
<para>
|
|
As mentioned above, you can pass the extra-data-length
|
|
to the 4th argument of <function>snd_card_create()</function>, i.e.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE,
|
|
sizeof(struct mychip), &card);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
struct <structname>mychip</structname> is the type of the chip record.
|
|
</para>
|
|
|
|
<para>
|
|
In return, the allocated record can be accessed as
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip *chip = card->private_data;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
With this method, you don't have to allocate twice.
|
|
The record is released together with the card instance.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="card-management-chip-specific-allocate-extra">
|
|
<title>2. Allocating an extra device.</title>
|
|
|
|
<para>
|
|
After allocating a card instance via
|
|
<function>snd_card_create()</function> (with
|
|
<constant>0</constant> on the 4th arg), call
|
|
<function>kzalloc()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_card *card;
|
|
struct mychip *chip;
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
|
|
.....
|
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The chip record should have the field to hold the card
|
|
pointer at least,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
struct snd_card *card;
|
|
....
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Then, set the card pointer in the returned chip instance.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
chip->card = card;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Next, initialize the fields, and register this chip
|
|
record as a low-level device with a specified
|
|
<parameter>ops</parameter>,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_device_ops ops = {
|
|
.dev_free = snd_mychip_dev_free,
|
|
};
|
|
....
|
|
snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<function>snd_mychip_dev_free()</function> is the
|
|
device-destructor function, which will call the real
|
|
destructor.
|
|
</para>
|
|
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_mychip_dev_free(struct snd_device *device)
|
|
{
|
|
return snd_mychip_free(device->device_data);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where <function>snd_mychip_free()</function> is the real destructor.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="card-management-registration">
|
|
<title>Registration and Release</title>
|
|
<para>
|
|
After all components are assigned, register the card instance
|
|
by calling <function>snd_card_register()</function>. Access
|
|
to the device files is enabled at this point. That is, before
|
|
<function>snd_card_register()</function> is called, the
|
|
components are safely inaccessible from external side. If this
|
|
call fails, exit the probe function after releasing the card via
|
|
<function>snd_card_free()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
For releasing the card instance, you can call simply
|
|
<function>snd_card_free()</function>. As mentioned earlier, all
|
|
components are released automatically by this call.
|
|
</para>
|
|
|
|
<para>
|
|
For a device which allows hotplugging, you can use
|
|
<function>snd_card_free_when_closed</function>. This one will
|
|
postpone the destruction until all devices are closed.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- PCI Resource Management -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="pci-resource">
|
|
<title>PCI Resource Management</title>
|
|
|
|
<section id="pci-resource-example">
|
|
<title>Full Code Example</title>
|
|
<para>
|
|
In this section, we'll complete the chip-specific constructor,
|
|
destructor and PCI entries. Example code is shown first,
|
|
below.
|
|
|
|
<example>
|
|
<title>PCI Resource Management Example</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
struct snd_card *card;
|
|
struct pci_dev *pci;
|
|
|
|
unsigned long port;
|
|
int irq;
|
|
};
|
|
|
|
static int snd_mychip_free(struct mychip *chip)
|
|
{
|
|
/* disable hardware here if any */
|
|
.... /* (not implemented in this document) */
|
|
|
|
/* release the irq */
|
|
if (chip->irq >= 0)
|
|
free_irq(chip->irq, chip);
|
|
/* release the I/O ports & memory */
|
|
pci_release_regions(chip->pci);
|
|
/* disable the PCI entry */
|
|
pci_disable_device(chip->pci);
|
|
/* release the data */
|
|
kfree(chip);
|
|
return 0;
|
|
}
|
|
|
|
/* chip-specific constructor */
|
|
static int snd_mychip_create(struct snd_card *card,
|
|
struct pci_dev *pci,
|
|
struct mychip **rchip)
|
|
{
|
|
struct mychip *chip;
|
|
int err;
|
|
static struct snd_device_ops ops = {
|
|
.dev_free = snd_mychip_dev_free,
|
|
};
|
|
|
|
*rchip = NULL;
|
|
|
|
/* initialize the PCI entry */
|
|
err = pci_enable_device(pci);
|
|
if (err < 0)
|
|
return err;
|
|
/* check PCI availability (28bit DMA) */
|
|
if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
|
|
pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
|
|
printk(KERN_ERR "error to set 28bit mask DMA\n");
|
|
pci_disable_device(pci);
|
|
return -ENXIO;
|
|
}
|
|
|
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL);
|
|
if (chip == NULL) {
|
|
pci_disable_device(pci);
|
|
return -ENOMEM;
|
|
}
|
|
|
|
/* initialize the stuff */
|
|
chip->card = card;
|
|
chip->pci = pci;
|
|
chip->irq = -1;
|
|
|
|
/* (1) PCI resource allocation */
|
|
err = pci_request_regions(pci, "My Chip");
|
|
if (err < 0) {
|
|
kfree(chip);
|
|
pci_disable_device(pci);
|
|
return err;
|
|
}
|
|
chip->port = pci_resource_start(pci, 0);
|
|
if (request_irq(pci->irq, snd_mychip_interrupt,
|
|
IRQF_SHARED, KBUILD_MODNAME, chip)) {
|
|
printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
|
|
snd_mychip_free(chip);
|
|
return -EBUSY;
|
|
}
|
|
chip->irq = pci->irq;
|
|
|
|
/* (2) initialization of the chip hardware */
|
|
.... /* (not implemented in this document) */
|
|
|
|
err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
|
|
if (err < 0) {
|
|
snd_mychip_free(chip);
|
|
return err;
|
|
}
|
|
|
|
snd_card_set_dev(card, &pci->dev);
|
|
|
|
*rchip = chip;
|
|
return 0;
|
|
}
|
|
|
|
/* PCI IDs */
|
|
static struct pci_device_id snd_mychip_ids[] = {
|
|
{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
|
|
PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
|
|
....
|
|
{ 0, }
|
|
};
|
|
MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
|
|
|
|
/* pci_driver definition */
|
|
static struct pci_driver driver = {
|
|
.name = KBUILD_MODNAME,
|
|
.id_table = snd_mychip_ids,
|
|
.probe = snd_mychip_probe,
|
|
.remove = snd_mychip_remove,
|
|
};
|
|
|
|
/* module initialization */
|
|
static int __init alsa_card_mychip_init(void)
|
|
{
|
|
return pci_register_driver(&driver);
|
|
}
|
|
|
|
/* module clean up */
|
|
static void __exit alsa_card_mychip_exit(void)
|
|
{
|
|
pci_unregister_driver(&driver);
|
|
}
|
|
|
|
module_init(alsa_card_mychip_init)
|
|
module_exit(alsa_card_mychip_exit)
|
|
|
|
EXPORT_NO_SYMBOLS; /* for old kernels only */
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pci-resource-some-haftas">
|
|
<title>Some Hafta's</title>
|
|
<para>
|
|
The allocation of PCI resources is done in the
|
|
<function>probe()</function> function, and usually an extra
|
|
<function>xxx_create()</function> function is written for this
|
|
purpose.
|
|
</para>
|
|
|
|
<para>
|
|
In the case of PCI devices, you first have to call
|
|
the <function>pci_enable_device()</function> function before
|
|
allocating resources. Also, you need to set the proper PCI DMA
|
|
mask to limit the accessed I/O range. In some cases, you might
|
|
need to call <function>pci_set_master()</function> function,
|
|
too.
|
|
</para>
|
|
|
|
<para>
|
|
Suppose the 28bit mask, and the code to be added would be like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
err = pci_enable_device(pci);
|
|
if (err < 0)
|
|
return err;
|
|
if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
|
|
pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
|
|
printk(KERN_ERR "error to set 28bit mask DMA\n");
|
|
pci_disable_device(pci);
|
|
return -ENXIO;
|
|
}
|
|
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pci-resource-resource-allocation">
|
|
<title>Resource Allocation</title>
|
|
<para>
|
|
The allocation of I/O ports and irqs is done via standard kernel
|
|
functions. Unlike ALSA ver.0.5.x., there are no helpers for
|
|
that. And these resources must be released in the destructor
|
|
function (see below). Also, on ALSA 0.9.x, you don't need to
|
|
allocate (pseudo-)DMA for PCI like in ALSA 0.5.x.
|
|
</para>
|
|
|
|
<para>
|
|
Now assume that the PCI device has an I/O port with 8 bytes
|
|
and an interrupt. Then struct <structname>mychip</structname> will have the
|
|
following fields:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
struct snd_card *card;
|
|
|
|
unsigned long port;
|
|
int irq;
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
For an I/O port (and also a memory region), you need to have
|
|
the resource pointer for the standard resource management. For
|
|
an irq, you have to keep only the irq number (integer). But you
|
|
need to initialize this number as -1 before actual allocation,
|
|
since irq 0 is valid. The port address and its resource pointer
|
|
can be initialized as null by
|
|
<function>kzalloc()</function> automatically, so you
|
|
don't have to take care of resetting them.
|
|
</para>
|
|
|
|
<para>
|
|
The allocation of an I/O port is done like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
err = pci_request_regions(pci, "My Chip");
|
|
if (err < 0) {
|
|
kfree(chip);
|
|
pci_disable_device(pci);
|
|
return err;
|
|
}
|
|
chip->port = pci_resource_start(pci, 0);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
<!-- obsolete -->
|
|
It will reserve the I/O port region of 8 bytes of the given
|
|
PCI device. The returned value, chip->res_port, is allocated
|
|
via <function>kmalloc()</function> by
|
|
<function>request_region()</function>. The pointer must be
|
|
released via <function>kfree()</function>, but there is a
|
|
problem with this. This issue will be explained later.
|
|
</para>
|
|
|
|
<para>
|
|
The allocation of an interrupt source is done like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
if (request_irq(pci->irq, snd_mychip_interrupt,
|
|
IRQF_SHARED, KBUILD_MODNAME, chip)) {
|
|
printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
|
|
snd_mychip_free(chip);
|
|
return -EBUSY;
|
|
}
|
|
chip->irq = pci->irq;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where <function>snd_mychip_interrupt()</function> is the
|
|
interrupt handler defined <link
|
|
linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>.
|
|
Note that chip->irq should be defined
|
|
only when <function>request_irq()</function> succeeded.
|
|
</para>
|
|
|
|
<para>
|
|
On the PCI bus, interrupts can be shared. Thus,
|
|
<constant>IRQF_SHARED</constant> is used as the interrupt flag of
|
|
<function>request_irq()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
The last argument of <function>request_irq()</function> is the
|
|
data pointer passed to the interrupt handler. Usually, the
|
|
chip-specific record is used for that, but you can use what you
|
|
like, too.
|
|
</para>
|
|
|
|
<para>
|
|
I won't give details about the interrupt handler at this
|
|
point, but at least its appearance can be explained now. The
|
|
interrupt handler looks usually like the following:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
|
|
{
|
|
struct mychip *chip = dev_id;
|
|
....
|
|
return IRQ_HANDLED;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Now let's write the corresponding destructor for the resources
|
|
above. The role of destructor is simple: disable the hardware
|
|
(if already activated) and release the resources. So far, we
|
|
have no hardware part, so the disabling code is not written here.
|
|
</para>
|
|
|
|
<para>
|
|
To release the resources, the <quote>check-and-release</quote>
|
|
method is a safer way. For the interrupt, do like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
if (chip->irq >= 0)
|
|
free_irq(chip->irq, chip);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
Since the irq number can start from 0, you should initialize
|
|
chip->irq with a negative value (e.g. -1), so that you can
|
|
check the validity of the irq number as above.
|
|
</para>
|
|
|
|
<para>
|
|
When you requested I/O ports or memory regions via
|
|
<function>pci_request_region()</function> or
|
|
<function>pci_request_regions()</function> like in this example,
|
|
release the resource(s) using the corresponding function,
|
|
<function>pci_release_region()</function> or
|
|
<function>pci_release_regions()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
pci_release_regions(chip->pci);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
When you requested manually via <function>request_region()</function>
|
|
or <function>request_mem_region</function>, you can release it via
|
|
<function>release_resource()</function>. Suppose that you keep
|
|
the resource pointer returned from <function>request_region()</function>
|
|
in chip->res_port, the release procedure looks like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
release_and_free_resource(chip->res_port);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Don't forget to call <function>pci_disable_device()</function>
|
|
before the end.
|
|
</para>
|
|
|
|
<para>
|
|
And finally, release the chip-specific record.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
kfree(chip);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
We didn't implement the hardware disabling part in the above.
|
|
If you need to do this, please note that the destructor may be
|
|
called even before the initialization of the chip is completed.
|
|
It would be better to have a flag to skip hardware disabling
|
|
if the hardware was not initialized yet.
|
|
</para>
|
|
|
|
<para>
|
|
When the chip-data is assigned to the card using
|
|
<function>snd_device_new()</function> with
|
|
<constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is
|
|
called at the last. That is, it is assured that all other
|
|
components like PCMs and controls have already been released.
|
|
You don't have to stop PCMs, etc. explicitly, but just
|
|
call low-level hardware stopping.
|
|
</para>
|
|
|
|
<para>
|
|
The management of a memory-mapped region is almost as same as
|
|
the management of an I/O port. You'll need three fields like
|
|
the following:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
....
|
|
unsigned long iobase_phys;
|
|
void __iomem *iobase_virt;
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
and the allocation would be like below:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
if ((err = pci_request_regions(pci, "My Chip")) < 0) {
|
|
kfree(chip);
|
|
return err;
|
|
}
|
|
chip->iobase_phys = pci_resource_start(pci, 0);
|
|
chip->iobase_virt = ioremap_nocache(chip->iobase_phys,
|
|
pci_resource_len(pci, 0));
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
and the corresponding destructor would be:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_mychip_free(struct mychip *chip)
|
|
{
|
|
....
|
|
if (chip->iobase_virt)
|
|
iounmap(chip->iobase_virt);
|
|
....
|
|
pci_release_regions(chip->pci);
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section id="pci-resource-device-struct">
|
|
<title>Registration of Device Struct</title>
|
|
<para>
|
|
At some point, typically after calling <function>snd_device_new()</function>,
|
|
you need to register the struct <structname>device</structname> of the chip
|
|
you're handling for udev and co. ALSA provides a macro for compatibility with
|
|
older kernels. Simply call like the following:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_card_set_dev(card, &pci->dev);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
so that it stores the PCI's device pointer to the card. This will be
|
|
referred by ALSA core functions later when the devices are registered.
|
|
</para>
|
|
<para>
|
|
In the case of non-PCI, pass the proper device struct pointer of the BUS
|
|
instead. (In the case of legacy ISA without PnP, you don't have to do
|
|
anything.)
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pci-resource-entries">
|
|
<title>PCI Entries</title>
|
|
<para>
|
|
So far, so good. Let's finish the missing PCI
|
|
stuff. At first, we need a
|
|
<structname>pci_device_id</structname> table for this
|
|
chipset. It's a table of PCI vendor/device ID number, and some
|
|
masks.
|
|
</para>
|
|
|
|
<para>
|
|
For example,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct pci_device_id snd_mychip_ids[] = {
|
|
{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
|
|
PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
|
|
....
|
|
{ 0, }
|
|
};
|
|
MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The first and second fields of
|
|
the <structname>pci_device_id</structname> structure are the vendor and
|
|
device IDs. If you have no reason to filter the matching
|
|
devices, you can leave the remaining fields as above. The last
|
|
field of the <structname>pci_device_id</structname> struct contains
|
|
private data for this entry. You can specify any value here, for
|
|
example, to define specific operations for supported device IDs.
|
|
Such an example is found in the intel8x0 driver.
|
|
</para>
|
|
|
|
<para>
|
|
The last entry of this list is the terminator. You must
|
|
specify this all-zero entry.
|
|
</para>
|
|
|
|
<para>
|
|
Then, prepare the <structname>pci_driver</structname> record:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct pci_driver driver = {
|
|
.name = KBUILD_MODNAME,
|
|
.id_table = snd_mychip_ids,
|
|
.probe = snd_mychip_probe,
|
|
.remove = snd_mychip_remove,
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>probe</structfield> and
|
|
<structfield>remove</structfield> functions have already
|
|
been defined in the previous sections.
|
|
The <structfield>name</structfield>
|
|
field is the name string of this device. Note that you must not
|
|
use a slash <quote>/</quote> in this string.
|
|
</para>
|
|
|
|
<para>
|
|
And at last, the module entries:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int __init alsa_card_mychip_init(void)
|
|
{
|
|
return pci_register_driver(&driver);
|
|
}
|
|
|
|
static void __exit alsa_card_mychip_exit(void)
|
|
{
|
|
pci_unregister_driver(&driver);
|
|
}
|
|
|
|
module_init(alsa_card_mychip_init)
|
|
module_exit(alsa_card_mychip_exit)
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Note that these module entries are tagged with
|
|
<parameter>__init</parameter> and
|
|
<parameter>__exit</parameter> prefixes.
|
|
</para>
|
|
|
|
<para>
|
|
Oh, one thing was forgotten. If you have no exported symbols,
|
|
you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels).
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
EXPORT_NO_SYMBOLS;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
That's all!
|
|
</para>
|
|
</section>
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- PCM Interface -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="pcm-interface">
|
|
<title>PCM Interface</title>
|
|
|
|
<section id="pcm-interface-general">
|
|
<title>General</title>
|
|
<para>
|
|
The PCM middle layer of ALSA is quite powerful and it is only
|
|
necessary for each driver to implement the low-level functions
|
|
to access its hardware.
|
|
</para>
|
|
|
|
<para>
|
|
For accessing to the PCM layer, you need to include
|
|
<filename><sound/pcm.h></filename> first. In addition,
|
|
<filename><sound/pcm_params.h></filename> might be needed
|
|
if you access to some functions related with hw_param.
|
|
</para>
|
|
|
|
<para>
|
|
Each card device can have up to four pcm instances. A pcm
|
|
instance corresponds to a pcm device file. The limitation of
|
|
number of instances comes only from the available bit size of
|
|
the Linux's device numbers. Once when 64bit device number is
|
|
used, we'll have more pcm instances available.
|
|
</para>
|
|
|
|
<para>
|
|
A pcm instance consists of pcm playback and capture streams,
|
|
and each pcm stream consists of one or more pcm substreams. Some
|
|
soundcards support multiple playback functions. For example,
|
|
emu10k1 has a PCM playback of 32 stereo substreams. In this case, at
|
|
each open, a free substream is (usually) automatically chosen
|
|
and opened. Meanwhile, when only one substream exists and it was
|
|
already opened, the successful open will either block
|
|
or error with <constant>EAGAIN</constant> according to the
|
|
file open mode. But you don't have to care about such details in your
|
|
driver. The PCM middle layer will take care of such work.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-example">
|
|
<title>Full Code Example</title>
|
|
<para>
|
|
The example code below does not include any hardware access
|
|
routines but shows only the skeleton, how to build up the PCM
|
|
interfaces.
|
|
|
|
<example>
|
|
<title>PCM Example Code</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#include <sound/pcm.h>
|
|
....
|
|
|
|
/* hardware definition */
|
|
static struct snd_pcm_hardware snd_mychip_playback_hw = {
|
|
.info = (SNDRV_PCM_INFO_MMAP |
|
|
SNDRV_PCM_INFO_INTERLEAVED |
|
|
SNDRV_PCM_INFO_BLOCK_TRANSFER |
|
|
SNDRV_PCM_INFO_MMAP_VALID),
|
|
.formats = SNDRV_PCM_FMTBIT_S16_LE,
|
|
.rates = SNDRV_PCM_RATE_8000_48000,
|
|
.rate_min = 8000,
|
|
.rate_max = 48000,
|
|
.channels_min = 2,
|
|
.channels_max = 2,
|
|
.buffer_bytes_max = 32768,
|
|
.period_bytes_min = 4096,
|
|
.period_bytes_max = 32768,
|
|
.periods_min = 1,
|
|
.periods_max = 1024,
|
|
};
|
|
|
|
/* hardware definition */
|
|
static struct snd_pcm_hardware snd_mychip_capture_hw = {
|
|
.info = (SNDRV_PCM_INFO_MMAP |
|
|
SNDRV_PCM_INFO_INTERLEAVED |
|
|
SNDRV_PCM_INFO_BLOCK_TRANSFER |
|
|
SNDRV_PCM_INFO_MMAP_VALID),
|
|
.formats = SNDRV_PCM_FMTBIT_S16_LE,
|
|
.rates = SNDRV_PCM_RATE_8000_48000,
|
|
.rate_min = 8000,
|
|
.rate_max = 48000,
|
|
.channels_min = 2,
|
|
.channels_max = 2,
|
|
.buffer_bytes_max = 32768,
|
|
.period_bytes_min = 4096,
|
|
.period_bytes_max = 32768,
|
|
.periods_min = 1,
|
|
.periods_max = 1024,
|
|
};
|
|
|
|
/* open callback */
|
|
static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
|
|
runtime->hw = snd_mychip_playback_hw;
|
|
/* more hardware-initialization will be done here */
|
|
....
|
|
return 0;
|
|
}
|
|
|
|
/* close callback */
|
|
static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
/* the hardware-specific codes will be here */
|
|
....
|
|
return 0;
|
|
|
|
}
|
|
|
|
/* open callback */
|
|
static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
|
|
runtime->hw = snd_mychip_capture_hw;
|
|
/* more hardware-initialization will be done here */
|
|
....
|
|
return 0;
|
|
}
|
|
|
|
/* close callback */
|
|
static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
/* the hardware-specific codes will be here */
|
|
....
|
|
return 0;
|
|
|
|
}
|
|
|
|
/* hw_params callback */
|
|
static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
|
|
struct snd_pcm_hw_params *hw_params)
|
|
{
|
|
return snd_pcm_lib_malloc_pages(substream,
|
|
params_buffer_bytes(hw_params));
|
|
}
|
|
|
|
/* hw_free callback */
|
|
static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
|
|
{
|
|
return snd_pcm_lib_free_pages(substream);
|
|
}
|
|
|
|
/* prepare callback */
|
|
static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
|
|
/* set up the hardware with the current configuration
|
|
* for example...
|
|
*/
|
|
mychip_set_sample_format(chip, runtime->format);
|
|
mychip_set_sample_rate(chip, runtime->rate);
|
|
mychip_set_channels(chip, runtime->channels);
|
|
mychip_set_dma_setup(chip, runtime->dma_addr,
|
|
chip->buffer_size,
|
|
chip->period_size);
|
|
return 0;
|
|
}
|
|
|
|
/* trigger callback */
|
|
static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
|
|
int cmd)
|
|
{
|
|
switch (cmd) {
|
|
case SNDRV_PCM_TRIGGER_START:
|
|
/* do something to start the PCM engine */
|
|
....
|
|
break;
|
|
case SNDRV_PCM_TRIGGER_STOP:
|
|
/* do something to stop the PCM engine */
|
|
....
|
|
break;
|
|
default:
|
|
return -EINVAL;
|
|
}
|
|
}
|
|
|
|
/* pointer callback */
|
|
static snd_pcm_uframes_t
|
|
snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
unsigned int current_ptr;
|
|
|
|
/* get the current hardware pointer */
|
|
current_ptr = mychip_get_hw_pointer(chip);
|
|
return current_ptr;
|
|
}
|
|
|
|
/* operators */
|
|
static struct snd_pcm_ops snd_mychip_playback_ops = {
|
|
.open = snd_mychip_playback_open,
|
|
.close = snd_mychip_playback_close,
|
|
.ioctl = snd_pcm_lib_ioctl,
|
|
.hw_params = snd_mychip_pcm_hw_params,
|
|
.hw_free = snd_mychip_pcm_hw_free,
|
|
.prepare = snd_mychip_pcm_prepare,
|
|
.trigger = snd_mychip_pcm_trigger,
|
|
.pointer = snd_mychip_pcm_pointer,
|
|
};
|
|
|
|
/* operators */
|
|
static struct snd_pcm_ops snd_mychip_capture_ops = {
|
|
.open = snd_mychip_capture_open,
|
|
.close = snd_mychip_capture_close,
|
|
.ioctl = snd_pcm_lib_ioctl,
|
|
.hw_params = snd_mychip_pcm_hw_params,
|
|
.hw_free = snd_mychip_pcm_hw_free,
|
|
.prepare = snd_mychip_pcm_prepare,
|
|
.trigger = snd_mychip_pcm_trigger,
|
|
.pointer = snd_mychip_pcm_pointer,
|
|
};
|
|
|
|
/*
|
|
* definitions of capture are omitted here...
|
|
*/
|
|
|
|
/* create a pcm device */
|
|
static int snd_mychip_new_pcm(struct mychip *chip)
|
|
{
|
|
struct snd_pcm *pcm;
|
|
int err;
|
|
|
|
err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
|
|
if (err < 0)
|
|
return err;
|
|
pcm->private_data = chip;
|
|
strcpy(pcm->name, "My Chip");
|
|
chip->pcm = pcm;
|
|
/* set operators */
|
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
|
|
&snd_mychip_playback_ops);
|
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
|
|
&snd_mychip_capture_ops);
|
|
/* pre-allocation of buffers */
|
|
/* NOTE: this may fail */
|
|
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
|
|
snd_dma_pci_data(chip->pci),
|
|
64*1024, 64*1024);
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-constructor">
|
|
<title>Constructor</title>
|
|
<para>
|
|
A pcm instance is allocated by the <function>snd_pcm_new()</function>
|
|
function. It would be better to create a constructor for pcm,
|
|
namely,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_mychip_new_pcm(struct mychip *chip)
|
|
{
|
|
struct snd_pcm *pcm;
|
|
int err;
|
|
|
|
err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
|
|
if (err < 0)
|
|
return err;
|
|
pcm->private_data = chip;
|
|
strcpy(pcm->name, "My Chip");
|
|
chip->pcm = pcm;
|
|
....
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The <function>snd_pcm_new()</function> function takes four
|
|
arguments. The first argument is the card pointer to which this
|
|
pcm is assigned, and the second is the ID string.
|
|
</para>
|
|
|
|
<para>
|
|
The third argument (<parameter>index</parameter>, 0 in the
|
|
above) is the index of this new pcm. It begins from zero. If
|
|
you create more than one pcm instances, specify the
|
|
different numbers in this argument. For example,
|
|
<parameter>index</parameter> = 1 for the second PCM device.
|
|
</para>
|
|
|
|
<para>
|
|
The fourth and fifth arguments are the number of substreams
|
|
for playback and capture, respectively. Here 1 is used for
|
|
both arguments. When no playback or capture substreams are available,
|
|
pass 0 to the corresponding argument.
|
|
</para>
|
|
|
|
<para>
|
|
If a chip supports multiple playbacks or captures, you can
|
|
specify more numbers, but they must be handled properly in
|
|
open/close, etc. callbacks. When you need to know which
|
|
substream you are referring to, then it can be obtained from
|
|
struct <structname>snd_pcm_substream</structname> data passed to each callback
|
|
as follows:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_pcm_substream *substream;
|
|
int index = substream->number;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
After the pcm is created, you need to set operators for each
|
|
pcm stream.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
|
|
&snd_mychip_playback_ops);
|
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
|
|
&snd_mychip_capture_ops);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The operators are defined typically like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_pcm_ops snd_mychip_playback_ops = {
|
|
.open = snd_mychip_pcm_open,
|
|
.close = snd_mychip_pcm_close,
|
|
.ioctl = snd_pcm_lib_ioctl,
|
|
.hw_params = snd_mychip_pcm_hw_params,
|
|
.hw_free = snd_mychip_pcm_hw_free,
|
|
.prepare = snd_mychip_pcm_prepare,
|
|
.trigger = snd_mychip_pcm_trigger,
|
|
.pointer = snd_mychip_pcm_pointer,
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
All the callbacks are described in the
|
|
<link linkend="pcm-interface-operators"><citetitle>
|
|
Operators</citetitle></link> subsection.
|
|
</para>
|
|
|
|
<para>
|
|
After setting the operators, you probably will want to
|
|
pre-allocate the buffer. For the pre-allocation, simply call
|
|
the following:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
|
|
snd_dma_pci_data(chip->pci),
|
|
64*1024, 64*1024);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
It will allocate a buffer up to 64kB as default.
|
|
Buffer management details will be described in the later section <link
|
|
linkend="buffer-and-memory"><citetitle>Buffer and Memory
|
|
Management</citetitle></link>.
|
|
</para>
|
|
|
|
<para>
|
|
Additionally, you can set some extra information for this pcm
|
|
in pcm->info_flags.
|
|
The available values are defined as
|
|
<constant>SNDRV_PCM_INFO_XXX</constant> in
|
|
<filename><sound/asound.h></filename>, which is used for
|
|
the hardware definition (described later). When your soundchip
|
|
supports only half-duplex, specify like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-destructor">
|
|
<title>... And the Destructor?</title>
|
|
<para>
|
|
The destructor for a pcm instance is not always
|
|
necessary. Since the pcm device will be released by the middle
|
|
layer code automatically, you don't have to call the destructor
|
|
explicitly.
|
|
</para>
|
|
|
|
<para>
|
|
The destructor would be necessary if you created
|
|
special records internally and needed to release them. In such a
|
|
case, set the destructor function to
|
|
pcm->private_free:
|
|
|
|
<example>
|
|
<title>PCM Instance with a Destructor</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void mychip_pcm_free(struct snd_pcm *pcm)
|
|
{
|
|
struct mychip *chip = snd_pcm_chip(pcm);
|
|
/* free your own data */
|
|
kfree(chip->my_private_pcm_data);
|
|
/* do what you like else */
|
|
....
|
|
}
|
|
|
|
static int snd_mychip_new_pcm(struct mychip *chip)
|
|
{
|
|
struct snd_pcm *pcm;
|
|
....
|
|
/* allocate your own data */
|
|
chip->my_private_pcm_data = kmalloc(...);
|
|
/* set the destructor */
|
|
pcm->private_data = chip;
|
|
pcm->private_free = mychip_pcm_free;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime">
|
|
<title>Runtime Pointer - The Chest of PCM Information</title>
|
|
<para>
|
|
When the PCM substream is opened, a PCM runtime instance is
|
|
allocated and assigned to the substream. This pointer is
|
|
accessible via <constant>substream->runtime</constant>.
|
|
This runtime pointer holds most information you need
|
|
to control the PCM: the copy of hw_params and sw_params configurations, the buffer
|
|
pointers, mmap records, spinlocks, etc.
|
|
</para>
|
|
|
|
<para>
|
|
The definition of runtime instance is found in
|
|
<filename><sound/pcm.h></filename>. Here are
|
|
the contents of this file:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct _snd_pcm_runtime {
|
|
/* -- Status -- */
|
|
struct snd_pcm_substream *trigger_master;
|
|
snd_timestamp_t trigger_tstamp; /* trigger timestamp */
|
|
int overrange;
|
|
snd_pcm_uframes_t avail_max;
|
|
snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */
|
|
snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
|
|
|
|
/* -- HW params -- */
|
|
snd_pcm_access_t access; /* access mode */
|
|
snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */
|
|
snd_pcm_subformat_t subformat; /* subformat */
|
|
unsigned int rate; /* rate in Hz */
|
|
unsigned int channels; /* channels */
|
|
snd_pcm_uframes_t period_size; /* period size */
|
|
unsigned int periods; /* periods */
|
|
snd_pcm_uframes_t buffer_size; /* buffer size */
|
|
unsigned int tick_time; /* tick time */
|
|
snd_pcm_uframes_t min_align; /* Min alignment for the format */
|
|
size_t byte_align;
|
|
unsigned int frame_bits;
|
|
unsigned int sample_bits;
|
|
unsigned int info;
|
|
unsigned int rate_num;
|
|
unsigned int rate_den;
|
|
|
|
/* -- SW params -- */
|
|
struct timespec tstamp_mode; /* mmap timestamp is updated */
|
|
unsigned int period_step;
|
|
unsigned int sleep_min; /* min ticks to sleep */
|
|
snd_pcm_uframes_t start_threshold;
|
|
snd_pcm_uframes_t stop_threshold;
|
|
snd_pcm_uframes_t silence_threshold; /* Silence filling happens when
|
|
noise is nearest than this */
|
|
snd_pcm_uframes_t silence_size; /* Silence filling size */
|
|
snd_pcm_uframes_t boundary; /* pointers wrap point */
|
|
|
|
snd_pcm_uframes_t silenced_start;
|
|
snd_pcm_uframes_t silenced_size;
|
|
|
|
snd_pcm_sync_id_t sync; /* hardware synchronization ID */
|
|
|
|
/* -- mmap -- */
|
|
volatile struct snd_pcm_mmap_status *status;
|
|
volatile struct snd_pcm_mmap_control *control;
|
|
atomic_t mmap_count;
|
|
|
|
/* -- locking / scheduling -- */
|
|
spinlock_t lock;
|
|
wait_queue_head_t sleep;
|
|
struct timer_list tick_timer;
|
|
struct fasync_struct *fasync;
|
|
|
|
/* -- private section -- */
|
|
void *private_data;
|
|
void (*private_free)(struct snd_pcm_runtime *runtime);
|
|
|
|
/* -- hardware description -- */
|
|
struct snd_pcm_hardware hw;
|
|
struct snd_pcm_hw_constraints hw_constraints;
|
|
|
|
/* -- interrupt callbacks -- */
|
|
void (*transfer_ack_begin)(struct snd_pcm_substream *substream);
|
|
void (*transfer_ack_end)(struct snd_pcm_substream *substream);
|
|
|
|
/* -- timer -- */
|
|
unsigned int timer_resolution; /* timer resolution */
|
|
|
|
/* -- DMA -- */
|
|
unsigned char *dma_area; /* DMA area */
|
|
dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */
|
|
size_t dma_bytes; /* size of DMA area */
|
|
|
|
struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */
|
|
|
|
#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
|
|
/* -- OSS things -- */
|
|
struct snd_pcm_oss_runtime oss;
|
|
#endif
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
For the operators (callbacks) of each sound driver, most of
|
|
these records are supposed to be read-only. Only the PCM
|
|
middle-layer changes / updates them. The exceptions are
|
|
the hardware description (hw), interrupt callbacks
|
|
(transfer_ack_xxx), DMA buffer information, and the private
|
|
data. Besides, if you use the standard buffer allocation
|
|
method via <function>snd_pcm_lib_malloc_pages()</function>,
|
|
you don't need to set the DMA buffer information by yourself.
|
|
</para>
|
|
|
|
<para>
|
|
In the sections below, important records are explained.
|
|
</para>
|
|
|
|
<section id="pcm-interface-runtime-hw">
|
|
<title>Hardware Description</title>
|
|
<para>
|
|
The hardware descriptor (struct <structname>snd_pcm_hardware</structname>)
|
|
contains the definitions of the fundamental hardware
|
|
configuration. Above all, you'll need to define this in
|
|
<link linkend="pcm-interface-operators-open-callback"><citetitle>
|
|
the open callback</citetitle></link>.
|
|
Note that the runtime instance holds the copy of the
|
|
descriptor, not the pointer to the existing descriptor. That
|
|
is, in the open callback, you can modify the copied descriptor
|
|
(<constant>runtime->hw</constant>) as you need. For example, if the maximum
|
|
number of channels is 1 only on some chip models, you can
|
|
still use the same hardware descriptor and change the
|
|
channels_max later:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
...
|
|
runtime->hw = snd_mychip_playback_hw; /* common definition */
|
|
if (chip->model == VERY_OLD_ONE)
|
|
runtime->hw.channels_max = 1;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Typically, you'll have a hardware descriptor as below:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_pcm_hardware snd_mychip_playback_hw = {
|
|
.info = (SNDRV_PCM_INFO_MMAP |
|
|
SNDRV_PCM_INFO_INTERLEAVED |
|
|
SNDRV_PCM_INFO_BLOCK_TRANSFER |
|
|
SNDRV_PCM_INFO_MMAP_VALID),
|
|
.formats = SNDRV_PCM_FMTBIT_S16_LE,
|
|
.rates = SNDRV_PCM_RATE_8000_48000,
|
|
.rate_min = 8000,
|
|
.rate_max = 48000,
|
|
.channels_min = 2,
|
|
.channels_max = 2,
|
|
.buffer_bytes_max = 32768,
|
|
.period_bytes_min = 4096,
|
|
.period_bytes_max = 32768,
|
|
.periods_min = 1,
|
|
.periods_max = 1024,
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
The <structfield>info</structfield> field contains the type and
|
|
capabilities of this pcm. The bit flags are defined in
|
|
<filename><sound/asound.h></filename> as
|
|
<constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you
|
|
have to specify whether the mmap is supported and which
|
|
interleaved format is supported.
|
|
When the hardware supports mmap, add the
|
|
<constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the
|
|
hardware supports the interleaved or the non-interleaved
|
|
formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or
|
|
<constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must
|
|
be set, respectively. If both are supported, you can set both,
|
|
too.
|
|
</para>
|
|
|
|
<para>
|
|
In the above example, <constant>MMAP_VALID</constant> and
|
|
<constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap
|
|
mode. Usually both are set. Of course,
|
|
<constant>MMAP_VALID</constant> is set only if the mmap is
|
|
really supported.
|
|
</para>
|
|
|
|
<para>
|
|
The other possible flags are
|
|
<constant>SNDRV_PCM_INFO_PAUSE</constant> and
|
|
<constant>SNDRV_PCM_INFO_RESUME</constant>. The
|
|
<constant>PAUSE</constant> bit means that the pcm supports the
|
|
<quote>pause</quote> operation, while the
|
|
<constant>RESUME</constant> bit means that the pcm supports
|
|
the full <quote>suspend/resume</quote> operation.
|
|
If the <constant>PAUSE</constant> flag is set,
|
|
the <structfield>trigger</structfield> callback below
|
|
must handle the corresponding (pause push/release) commands.
|
|
The suspend/resume trigger commands can be defined even without
|
|
the <constant>RESUME</constant> flag. See <link
|
|
linkend="power-management"><citetitle>
|
|
Power Management</citetitle></link> section for details.
|
|
</para>
|
|
|
|
<para>
|
|
When the PCM substreams can be synchronized (typically,
|
|
synchronized start/stop of a playback and a capture streams),
|
|
you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>,
|
|
too. In this case, you'll need to check the linked-list of
|
|
PCM substreams in the trigger callback. This will be
|
|
described in the later section.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<structfield>formats</structfield> field contains the bit-flags
|
|
of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>).
|
|
If the hardware supports more than one format, give all or'ed
|
|
bits. In the example above, the signed 16bit little-endian
|
|
format is specified.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<structfield>rates</structfield> field contains the bit-flags of
|
|
supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>).
|
|
When the chip supports continuous rates, pass
|
|
<constant>CONTINUOUS</constant> bit additionally.
|
|
The pre-defined rate bits are provided only for typical
|
|
rates. If your chip supports unconventional rates, you need to add
|
|
the <constant>KNOT</constant> bit and set up the hardware
|
|
constraint manually (explained later).
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<structfield>rate_min</structfield> and
|
|
<structfield>rate_max</structfield> define the minimum and
|
|
maximum sample rate. This should correspond somehow to
|
|
<structfield>rates</structfield> bits.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<structfield>channel_min</structfield> and
|
|
<structfield>channel_max</structfield>
|
|
define, as you might already expected, the minimum and maximum
|
|
number of channels.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<structfield>buffer_bytes_max</structfield> defines the
|
|
maximum buffer size in bytes. There is no
|
|
<structfield>buffer_bytes_min</structfield> field, since
|
|
it can be calculated from the minimum period size and the
|
|
minimum number of periods.
|
|
Meanwhile, <structfield>period_bytes_min</structfield> and
|
|
define the minimum and maximum size of the period in bytes.
|
|
<structfield>periods_max</structfield> and
|
|
<structfield>periods_min</structfield> define the maximum and
|
|
minimum number of periods in the buffer.
|
|
</para>
|
|
|
|
<para>
|
|
The <quote>period</quote> is a term that corresponds to
|
|
a fragment in the OSS world. The period defines the size at
|
|
which a PCM interrupt is generated. This size strongly
|
|
depends on the hardware.
|
|
Generally, the smaller period size will give you more
|
|
interrupts, that is, more controls.
|
|
In the case of capture, this size defines the input latency.
|
|
On the other hand, the whole buffer size defines the
|
|
output latency for the playback direction.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
There is also a field <structfield>fifo_size</structfield>.
|
|
This specifies the size of the hardware FIFO, but currently it
|
|
is neither used in the driver nor in the alsa-lib. So, you
|
|
can ignore this field.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime-config">
|
|
<title>PCM Configurations</title>
|
|
<para>
|
|
Ok, let's go back again to the PCM runtime records.
|
|
The most frequently referred records in the runtime instance are
|
|
the PCM configurations.
|
|
The PCM configurations are stored in the runtime instance
|
|
after the application sends <type>hw_params</type> data via
|
|
alsa-lib. There are many fields copied from hw_params and
|
|
sw_params structs. For example,
|
|
<structfield>format</structfield> holds the format type
|
|
chosen by the application. This field contains the enum value
|
|
<constant>SNDRV_PCM_FORMAT_XXX</constant>.
|
|
</para>
|
|
|
|
<para>
|
|
One thing to be noted is that the configured buffer and period
|
|
sizes are stored in <quote>frames</quote> in the runtime.
|
|
In the ALSA world, 1 frame = channels * samples-size.
|
|
For conversion between frames and bytes, you can use the
|
|
<function>frames_to_bytes()</function> and
|
|
<function>bytes_to_frames()</function> helper functions.
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
period_bytes = frames_to_bytes(runtime, runtime->period_size);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Also, many software parameters (sw_params) are
|
|
stored in frames, too. Please check the type of the field.
|
|
<type>snd_pcm_uframes_t</type> is for the frames as unsigned
|
|
integer while <type>snd_pcm_sframes_t</type> is for the frames
|
|
as signed integer.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime-dma">
|
|
<title>DMA Buffer Information</title>
|
|
<para>
|
|
The DMA buffer is defined by the following four fields,
|
|
<structfield>dma_area</structfield>,
|
|
<structfield>dma_addr</structfield>,
|
|
<structfield>dma_bytes</structfield> and
|
|
<structfield>dma_private</structfield>.
|
|
The <structfield>dma_area</structfield> holds the buffer
|
|
pointer (the logical address). You can call
|
|
<function>memcpy</function> from/to
|
|
this pointer. Meanwhile, <structfield>dma_addr</structfield>
|
|
holds the physical address of the buffer. This field is
|
|
specified only when the buffer is a linear buffer.
|
|
<structfield>dma_bytes</structfield> holds the size of buffer
|
|
in bytes. <structfield>dma_private</structfield> is used for
|
|
the ALSA DMA allocator.
|
|
</para>
|
|
|
|
<para>
|
|
If you use a standard ALSA function,
|
|
<function>snd_pcm_lib_malloc_pages()</function>, for
|
|
allocating the buffer, these fields are set by the ALSA middle
|
|
layer, and you should <emphasis>not</emphasis> change them by
|
|
yourself. You can read them but not write them.
|
|
On the other hand, if you want to allocate the buffer by
|
|
yourself, you'll need to manage it in hw_params callback.
|
|
At least, <structfield>dma_bytes</structfield> is mandatory.
|
|
<structfield>dma_area</structfield> is necessary when the
|
|
buffer is mmapped. If your driver doesn't support mmap, this
|
|
field is not necessary. <structfield>dma_addr</structfield>
|
|
is also optional. You can use
|
|
<structfield>dma_private</structfield> as you like, too.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime-status">
|
|
<title>Running Status</title>
|
|
<para>
|
|
The running status can be referred via <constant>runtime->status</constant>.
|
|
This is the pointer to the struct <structname>snd_pcm_mmap_status</structname>
|
|
record. For example, you can get the current DMA hardware
|
|
pointer via <constant>runtime->status->hw_ptr</constant>.
|
|
</para>
|
|
|
|
<para>
|
|
The DMA application pointer can be referred via
|
|
<constant>runtime->control</constant>, which points to the
|
|
struct <structname>snd_pcm_mmap_control</structname> record.
|
|
However, accessing directly to this value is not recommended.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime-private">
|
|
<title>Private Data</title>
|
|
<para>
|
|
You can allocate a record for the substream and store it in
|
|
<constant>runtime->private_data</constant>. Usually, this
|
|
is done in
|
|
<link linkend="pcm-interface-operators-open-callback"><citetitle>
|
|
the open callback</citetitle></link>.
|
|
Don't mix this with <constant>pcm->private_data</constant>.
|
|
The <constant>pcm->private_data</constant> usually points to the
|
|
chip instance assigned statically at the creation of PCM, while the
|
|
<constant>runtime->private_data</constant> points to a dynamic
|
|
data structure created at the PCM open callback.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream)
|
|
{
|
|
struct my_pcm_data *data;
|
|
....
|
|
data = kmalloc(sizeof(*data), GFP_KERNEL);
|
|
substream->runtime->private_data = data;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The allocated object must be released in
|
|
<link linkend="pcm-interface-operators-open-callback"><citetitle>
|
|
the close callback</citetitle></link>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-runtime-intr">
|
|
<title>Interrupt Callbacks</title>
|
|
<para>
|
|
The field <structfield>transfer_ack_begin</structfield> and
|
|
<structfield>transfer_ack_end</structfield> are called at
|
|
the beginning and at the end of
|
|
<function>snd_pcm_period_elapsed()</function>, respectively.
|
|
</para>
|
|
</section>
|
|
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators">
|
|
<title>Operators</title>
|
|
<para>
|
|
OK, now let me give details about each pcm callback
|
|
(<parameter>ops</parameter>). In general, every callback must
|
|
return 0 if successful, or a negative error number
|
|
such as <constant>-EINVAL</constant>. To choose an appropriate
|
|
error number, it is advised to check what value other parts of
|
|
the kernel return when the same kind of request fails.
|
|
</para>
|
|
|
|
<para>
|
|
The callback function takes at least the argument with
|
|
<structname>snd_pcm_substream</structname> pointer. To retrieve
|
|
the chip record from the given substream instance, you can use the
|
|
following macro.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
int xxx() {
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
The macro reads <constant>substream->private_data</constant>,
|
|
which is a copy of <constant>pcm->private_data</constant>.
|
|
You can override the former if you need to assign different data
|
|
records per PCM substream. For example, the cmi8330 driver assigns
|
|
different private_data for playback and capture directions,
|
|
because it uses two different codecs (SB- and AD-compatible) for
|
|
different directions.
|
|
</para>
|
|
|
|
<section id="pcm-interface-operators-open-callback">
|
|
<title>open callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
This is called when a pcm substream is opened.
|
|
</para>
|
|
|
|
<para>
|
|
At least, here you have to initialize the runtime->hw
|
|
record. Typically, this is done by like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream)
|
|
{
|
|
struct mychip *chip = snd_pcm_substream_chip(substream);
|
|
struct snd_pcm_runtime *runtime = substream->runtime;
|
|
|
|
runtime->hw = snd_mychip_playback_hw;
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where <parameter>snd_mychip_playback_hw</parameter> is the
|
|
pre-defined hardware description.
|
|
</para>
|
|
|
|
<para>
|
|
You can allocate a private data in this callback, as described
|
|
in <link linkend="pcm-interface-runtime-private"><citetitle>
|
|
Private Data</citetitle></link> section.
|
|
</para>
|
|
|
|
<para>
|
|
If the hardware configuration needs more constraints, set the
|
|
hardware constraints here, too.
|
|
See <link linkend="pcm-interface-constraints"><citetitle>
|
|
Constraints</citetitle></link> for more details.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-close-callback">
|
|
<title>close callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_close(struct snd_pcm_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
Obviously, this is called when a pcm substream is closed.
|
|
</para>
|
|
|
|
<para>
|
|
Any private instance for a pcm substream allocated in the
|
|
open callback will be released here.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_close(struct snd_pcm_substream *substream)
|
|
{
|
|
....
|
|
kfree(substream->runtime->private_data);
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-ioctl-callback">
|
|
<title>ioctl callback</title>
|
|
<para>
|
|
This is used for any special call to pcm ioctls. But
|
|
usually you can pass a generic ioctl callback,
|
|
<function>snd_pcm_lib_ioctl</function>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-hw-params-callback">
|
|
<title>hw_params callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_hw_params(struct snd_pcm_substream *substream,
|
|
struct snd_pcm_hw_params *hw_params);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
This is called when the hardware parameter
|
|
(<structfield>hw_params</structfield>) is set
|
|
up by the application,
|
|
that is, once when the buffer size, the period size, the
|
|
format, etc. are defined for the pcm substream.
|
|
</para>
|
|
|
|
<para>
|
|
Many hardware setups should be done in this callback,
|
|
including the allocation of buffers.
|
|
</para>
|
|
|
|
<para>
|
|
Parameters to be initialized are retrieved by
|
|
<function>params_xxx()</function> macros. To allocate
|
|
buffer, you can call a helper function,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params));
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<function>snd_pcm_lib_malloc_pages()</function> is available
|
|
only when the DMA buffers have been pre-allocated.
|
|
See the section <link
|
|
linkend="buffer-and-memory-buffer-types"><citetitle>
|
|
Buffer Types</citetitle></link> for more details.
|
|
</para>
|
|
|
|
<para>
|
|
Note that this and <structfield>prepare</structfield> callbacks
|
|
may be called multiple times per initialization.
|
|
For example, the OSS emulation may
|
|
call these callbacks at each change via its ioctl.
|
|
</para>
|
|
|
|
<para>
|
|
Thus, you need to be careful not to allocate the same buffers
|
|
many times, which will lead to memory leaks! Calling the
|
|
helper function above many times is OK. It will release the
|
|
previous buffer automatically when it was already allocated.
|
|
</para>
|
|
|
|
<para>
|
|
Another note is that this callback is non-atomic
|
|
(schedulable). This is important, because the
|
|
<structfield>trigger</structfield> callback
|
|
is atomic (non-schedulable). That is, mutexes or any
|
|
schedule-related functions are not available in
|
|
<structfield>trigger</structfield> callback.
|
|
Please see the subsection
|
|
<link linkend="pcm-interface-atomicity"><citetitle>
|
|
Atomicity</citetitle></link> for details.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-hw-free-callback">
|
|
<title>hw_free callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_hw_free(struct snd_pcm_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
This is called to release the resources allocated via
|
|
<structfield>hw_params</structfield>. For example, releasing the
|
|
buffer via
|
|
<function>snd_pcm_lib_malloc_pages()</function> is done by
|
|
calling the following:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_lib_free_pages(substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
This function is always called before the close callback is called.
|
|
Also, the callback may be called multiple times, too.
|
|
Keep track whether the resource was already released.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-prepare-callback">
|
|
<title>prepare callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_prepare(struct snd_pcm_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
This callback is called when the pcm is
|
|
<quote>prepared</quote>. You can set the format type, sample
|
|
rate, etc. here. The difference from
|
|
<structfield>hw_params</structfield> is that the
|
|
<structfield>prepare</structfield> callback will be called each
|
|
time
|
|
<function>snd_pcm_prepare()</function> is called, i.e. when
|
|
recovering after underruns, etc.
|
|
</para>
|
|
|
|
<para>
|
|
Note that this callback is now non-atomic.
|
|
You can use schedule-related functions safely in this callback.
|
|
</para>
|
|
|
|
<para>
|
|
In this and the following callbacks, you can refer to the
|
|
values via the runtime record,
|
|
substream->runtime.
|
|
For example, to get the current
|
|
rate, format or channels, access to
|
|
runtime->rate,
|
|
runtime->format or
|
|
runtime->channels, respectively.
|
|
The physical address of the allocated buffer is set to
|
|
runtime->dma_area. The buffer and period sizes are
|
|
in runtime->buffer_size and runtime->period_size,
|
|
respectively.
|
|
</para>
|
|
|
|
<para>
|
|
Be careful that this callback will be called many times at
|
|
each setup, too.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-trigger-callback">
|
|
<title>trigger callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
This is called when the pcm is started, stopped or paused.
|
|
</para>
|
|
|
|
<para>
|
|
Which action is specified in the second argument,
|
|
<constant>SNDRV_PCM_TRIGGER_XXX</constant> in
|
|
<filename><sound/pcm.h></filename>. At least,
|
|
the <constant>START</constant> and <constant>STOP</constant>
|
|
commands must be defined in this callback.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
switch (cmd) {
|
|
case SNDRV_PCM_TRIGGER_START:
|
|
/* do something to start the PCM engine */
|
|
break;
|
|
case SNDRV_PCM_TRIGGER_STOP:
|
|
/* do something to stop the PCM engine */
|
|
break;
|
|
default:
|
|
return -EINVAL;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
When the pcm supports the pause operation (given in the info
|
|
field of the hardware table), the <constant>PAUSE_PUSH</constant>
|
|
and <constant>PAUSE_RELEASE</constant> commands must be
|
|
handled here, too. The former is the command to pause the pcm,
|
|
and the latter to restart the pcm again.
|
|
</para>
|
|
|
|
<para>
|
|
When the pcm supports the suspend/resume operation,
|
|
regardless of full or partial suspend/resume support,
|
|
the <constant>SUSPEND</constant> and <constant>RESUME</constant>
|
|
commands must be handled, too.
|
|
These commands are issued when the power-management status is
|
|
changed. Obviously, the <constant>SUSPEND</constant> and
|
|
<constant>RESUME</constant> commands
|
|
suspend and resume the pcm substream, and usually, they
|
|
are identical to the <constant>STOP</constant> and
|
|
<constant>START</constant> commands, respectively.
|
|
See the <link linkend="power-management"><citetitle>
|
|
Power Management</citetitle></link> section for details.
|
|
</para>
|
|
|
|
<para>
|
|
As mentioned, this callback is atomic. You cannot call
|
|
functions which may sleep.
|
|
The trigger callback should be as minimal as possible,
|
|
just really triggering the DMA. The other stuff should be
|
|
initialized hw_params and prepare callbacks properly
|
|
beforehand.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-pointer-callback">
|
|
<title>pointer callback</title>
|
|
<para>
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
This callback is called when the PCM middle layer inquires
|
|
the current hardware position on the buffer. The position must
|
|
be returned in frames,
|
|
ranging from 0 to buffer_size - 1.
|
|
</para>
|
|
|
|
<para>
|
|
This is called usually from the buffer-update routine in the
|
|
pcm middle layer, which is invoked when
|
|
<function>snd_pcm_period_elapsed()</function> is called in the
|
|
interrupt routine. Then the pcm middle layer updates the
|
|
position and calculates the available space, and wakes up the
|
|
sleeping poll threads, etc.
|
|
</para>
|
|
|
|
<para>
|
|
This callback is also atomic.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-copy-silence">
|
|
<title>copy and silence callbacks</title>
|
|
<para>
|
|
These callbacks are not mandatory, and can be omitted in
|
|
most cases. These callbacks are used when the hardware buffer
|
|
cannot be in the normal memory space. Some chips have their
|
|
own buffer on the hardware which is not mappable. In such a
|
|
case, you have to transfer the data manually from the memory
|
|
buffer to the hardware buffer. Or, if the buffer is
|
|
non-contiguous on both physical and virtual memory spaces,
|
|
these callbacks must be defined, too.
|
|
</para>
|
|
|
|
<para>
|
|
If these two callbacks are defined, copy and set-silence
|
|
operations are done by them. The detailed will be described in
|
|
the later section <link
|
|
linkend="buffer-and-memory"><citetitle>Buffer and Memory
|
|
Management</citetitle></link>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-ack">
|
|
<title>ack callback</title>
|
|
<para>
|
|
This callback is also not mandatory. This callback is called
|
|
when the appl_ptr is updated in read or write operations.
|
|
Some drivers like emu10k1-fx and cs46xx need to track the
|
|
current appl_ptr for the internal buffer, and this callback
|
|
is useful only for such a purpose.
|
|
</para>
|
|
<para>
|
|
This callback is atomic.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-operators-page-callback">
|
|
<title>page callback</title>
|
|
|
|
<para>
|
|
This callback is optional too. This callback is used
|
|
mainly for non-contiguous buffers. The mmap calls this
|
|
callback to get the page address. Some examples will be
|
|
explained in the later section <link
|
|
linkend="buffer-and-memory"><citetitle>Buffer and Memory
|
|
Management</citetitle></link>, too.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="pcm-interface-interrupt-handler">
|
|
<title>Interrupt Handler</title>
|
|
<para>
|
|
The rest of pcm stuff is the PCM interrupt handler. The
|
|
role of PCM interrupt handler in the sound driver is to update
|
|
the buffer position and to tell the PCM middle layer when the
|
|
buffer position goes across the prescribed period size. To
|
|
inform this, call the <function>snd_pcm_period_elapsed()</function>
|
|
function.
|
|
</para>
|
|
|
|
<para>
|
|
There are several types of sound chips to generate the interrupts.
|
|
</para>
|
|
|
|
<section id="pcm-interface-interrupt-handler-boundary">
|
|
<title>Interrupts at the period (fragment) boundary</title>
|
|
<para>
|
|
This is the most frequently found type: the hardware
|
|
generates an interrupt at each period boundary.
|
|
In this case, you can call
|
|
<function>snd_pcm_period_elapsed()</function> at each
|
|
interrupt.
|
|
</para>
|
|
|
|
<para>
|
|
<function>snd_pcm_period_elapsed()</function> takes the
|
|
substream pointer as its argument. Thus, you need to keep the
|
|
substream pointer accessible from the chip instance. For
|
|
example, define substream field in the chip record to hold the
|
|
current running substream pointer, and set the pointer value
|
|
at open callback (and reset at close callback).
|
|
</para>
|
|
|
|
<para>
|
|
If you acquire a spinlock in the interrupt handler, and the
|
|
lock is used in other pcm callbacks, too, then you have to
|
|
release the lock before calling
|
|
<function>snd_pcm_period_elapsed()</function>, because
|
|
<function>snd_pcm_period_elapsed()</function> calls other pcm
|
|
callbacks inside.
|
|
</para>
|
|
|
|
<para>
|
|
Typical code would be like:
|
|
|
|
<example>
|
|
<title>Interrupt Handler Case #1</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
|
|
{
|
|
struct mychip *chip = dev_id;
|
|
spin_lock(&chip->lock);
|
|
....
|
|
if (pcm_irq_invoked(chip)) {
|
|
/* call updater, unlock before it */
|
|
spin_unlock(&chip->lock);
|
|
snd_pcm_period_elapsed(chip->substream);
|
|
spin_lock(&chip->lock);
|
|
/* acknowledge the interrupt if necessary */
|
|
}
|
|
....
|
|
spin_unlock(&chip->lock);
|
|
return IRQ_HANDLED;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-interrupt-handler-timer">
|
|
<title>High frequency timer interrupts</title>
|
|
<para>
|
|
This happens when the hardware doesn't generate interrupts
|
|
at the period boundary but issues timer interrupts at a fixed
|
|
timer rate (e.g. es1968 or ymfpci drivers).
|
|
In this case, you need to check the current hardware
|
|
position and accumulate the processed sample length at each
|
|
interrupt. When the accumulated size exceeds the period
|
|
size, call
|
|
<function>snd_pcm_period_elapsed()</function> and reset the
|
|
accumulator.
|
|
</para>
|
|
|
|
<para>
|
|
Typical code would be like the following.
|
|
|
|
<example>
|
|
<title>Interrupt Handler Case #2</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
|
|
{
|
|
struct mychip *chip = dev_id;
|
|
spin_lock(&chip->lock);
|
|
....
|
|
if (pcm_irq_invoked(chip)) {
|
|
unsigned int last_ptr, size;
|
|
/* get the current hardware pointer (in frames) */
|
|
last_ptr = get_hw_ptr(chip);
|
|
/* calculate the processed frames since the
|
|
* last update
|
|
*/
|
|
if (last_ptr < chip->last_ptr)
|
|
size = runtime->buffer_size + last_ptr
|
|
- chip->last_ptr;
|
|
else
|
|
size = last_ptr - chip->last_ptr;
|
|
/* remember the last updated point */
|
|
chip->last_ptr = last_ptr;
|
|
/* accumulate the size */
|
|
chip->size += size;
|
|
/* over the period boundary? */
|
|
if (chip->size >= runtime->period_size) {
|
|
/* reset the accumulator */
|
|
chip->size %= runtime->period_size;
|
|
/* call updater */
|
|
spin_unlock(&chip->lock);
|
|
snd_pcm_period_elapsed(substream);
|
|
spin_lock(&chip->lock);
|
|
}
|
|
/* acknowledge the interrupt if necessary */
|
|
}
|
|
....
|
|
spin_unlock(&chip->lock);
|
|
return IRQ_HANDLED;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="pcm-interface-interrupt-handler-both">
|
|
<title>On calling <function>snd_pcm_period_elapsed()</function></title>
|
|
<para>
|
|
In both cases, even if more than one period are elapsed, you
|
|
don't have to call
|
|
<function>snd_pcm_period_elapsed()</function> many times. Call
|
|
only once. And the pcm layer will check the current hardware
|
|
pointer and update to the latest status.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="pcm-interface-atomicity">
|
|
<title>Atomicity</title>
|
|
<para>
|
|
One of the most important (and thus difficult to debug) problems
|
|
in kernel programming are race conditions.
|
|
In the Linux kernel, they are usually avoided via spin-locks, mutexes
|
|
or semaphores. In general, if a race condition can happen
|
|
in an interrupt handler, it has to be managed atomically, and you
|
|
have to use a spinlock to protect the critical session. If the
|
|
critical section is not in interrupt handler code and
|
|
if taking a relatively long time to execute is acceptable, you
|
|
should use mutexes or semaphores instead.
|
|
</para>
|
|
|
|
<para>
|
|
As already seen, some pcm callbacks are atomic and some are
|
|
not. For example, the <parameter>hw_params</parameter> callback is
|
|
non-atomic, while <parameter>trigger</parameter> callback is
|
|
atomic. This means, the latter is called already in a spinlock
|
|
held by the PCM middle layer. Please take this atomicity into
|
|
account when you choose a locking scheme in the callbacks.
|
|
</para>
|
|
|
|
<para>
|
|
In the atomic callbacks, you cannot use functions which may call
|
|
<function>schedule</function> or go to
|
|
<function>sleep</function>. Semaphores and mutexes can sleep,
|
|
and hence they cannot be used inside the atomic callbacks
|
|
(e.g. <parameter>trigger</parameter> callback).
|
|
To implement some delay in such a callback, please use
|
|
<function>udelay()</function> or <function>mdelay()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
All three atomic callbacks (trigger, pointer, and ack) are
|
|
called with local interrupts disabled.
|
|
</para>
|
|
|
|
</section>
|
|
<section id="pcm-interface-constraints">
|
|
<title>Constraints</title>
|
|
<para>
|
|
If your chip supports unconventional sample rates, or only the
|
|
limited samples, you need to set a constraint for the
|
|
condition.
|
|
</para>
|
|
|
|
<para>
|
|
For example, in order to restrict the sample rates in the some
|
|
supported values, use
|
|
<function>snd_pcm_hw_constraint_list()</function>.
|
|
You need to call this function in the open callback.
|
|
|
|
<example>
|
|
<title>Example of Hardware Constraints</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static unsigned int rates[] =
|
|
{4000, 10000, 22050, 44100};
|
|
static struct snd_pcm_hw_constraint_list constraints_rates = {
|
|
.count = ARRAY_SIZE(rates),
|
|
.list = rates,
|
|
.mask = 0,
|
|
};
|
|
|
|
static int snd_mychip_pcm_open(struct snd_pcm_substream *substream)
|
|
{
|
|
int err;
|
|
....
|
|
err = snd_pcm_hw_constraint_list(substream->runtime, 0,
|
|
SNDRV_PCM_HW_PARAM_RATE,
|
|
&constraints_rates);
|
|
if (err < 0)
|
|
return err;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
There are many different constraints.
|
|
Look at <filename>sound/pcm.h</filename> for a complete list.
|
|
You can even define your own constraint rules.
|
|
For example, let's suppose my_chip can manage a substream of 1 channel
|
|
if and only if the format is S16_LE, otherwise it supports any format
|
|
specified in the <structname>snd_pcm_hardware</structname> structure (or in any
|
|
other constraint_list). You can build a rule like this:
|
|
|
|
<example>
|
|
<title>Example of Hardware Constraints for Channels</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,
|
|
struct snd_pcm_hw_rule *rule)
|
|
{
|
|
struct snd_interval *c = hw_param_interval(params,
|
|
SNDRV_PCM_HW_PARAM_CHANNELS);
|
|
struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
|
|
struct snd_interval ch;
|
|
|
|
snd_interval_any(&ch);
|
|
if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
|
|
ch.min = ch.max = 1;
|
|
ch.integer = 1;
|
|
return snd_interval_refine(c, &ch);
|
|
}
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
Then you need to call this function to add your rule:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
|
|
hw_rule_channels_by_format, NULL,
|
|
SNDRV_PCM_HW_PARAM_FORMAT, -1);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The rule function is called when an application sets the PCM
|
|
format, and it refines the number of channels accordingly.
|
|
But an application may set the number of channels before
|
|
setting the format. Thus you also need to define the inverse rule:
|
|
|
|
<example>
|
|
<title>Example of Hardware Constraints for Formats</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,
|
|
struct snd_pcm_hw_rule *rule)
|
|
{
|
|
struct snd_interval *c = hw_param_interval(params,
|
|
SNDRV_PCM_HW_PARAM_CHANNELS);
|
|
struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
|
|
struct snd_mask fmt;
|
|
|
|
snd_mask_any(&fmt); /* Init the struct */
|
|
if (c->min < 2) {
|
|
fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
|
|
return snd_mask_refine(f, &fmt);
|
|
}
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
...and in the open callback:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
|
|
hw_rule_format_by_channels, NULL,
|
|
SNDRV_PCM_HW_PARAM_CHANNELS, -1);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
I won't give more details here, rather I
|
|
would like to say, <quote>Luke, use the source.</quote>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Control Interface -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="control-interface">
|
|
<title>Control Interface</title>
|
|
|
|
<section id="control-interface-general">
|
|
<title>General</title>
|
|
<para>
|
|
The control interface is used widely for many switches,
|
|
sliders, etc. which are accessed from user-space. Its most
|
|
important use is the mixer interface. In other words, since ALSA
|
|
0.9.x, all the mixer stuff is implemented on the control kernel API.
|
|
</para>
|
|
|
|
<para>
|
|
ALSA has a well-defined AC97 control module. If your chip
|
|
supports only the AC97 and nothing else, you can skip this
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
The control API is defined in
|
|
<filename><sound/control.h></filename>.
|
|
Include this file if you want to add your own controls.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-definition">
|
|
<title>Definition of Controls</title>
|
|
<para>
|
|
To create a new control, you need to define the
|
|
following three
|
|
callbacks: <structfield>info</structfield>,
|
|
<structfield>get</structfield> and
|
|
<structfield>put</structfield>. Then, define a
|
|
struct <structname>snd_kcontrol_new</structname> record, such as:
|
|
|
|
<example>
|
|
<title>Definition of a Control</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_kcontrol_new my_control = {
|
|
.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
|
|
.name = "PCM Playback Switch",
|
|
.index = 0,
|
|
.access = SNDRV_CTL_ELEM_ACCESS_READWRITE,
|
|
.private_value = 0xffff,
|
|
.info = my_control_info,
|
|
.get = my_control_get,
|
|
.put = my_control_put
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>iface</structfield> field specifies the control
|
|
type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which
|
|
is usually <constant>MIXER</constant>.
|
|
Use <constant>CARD</constant> for global controls that are not
|
|
logically part of the mixer.
|
|
If the control is closely associated with some specific device on
|
|
the sound card, use <constant>HWDEP</constant>,
|
|
<constant>PCM</constant>, <constant>RAWMIDI</constant>,
|
|
<constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and
|
|
specify the device number with the
|
|
<structfield>device</structfield> and
|
|
<structfield>subdevice</structfield> fields.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>name</structfield> is the name identifier
|
|
string. Since ALSA 0.9.x, the control name is very important,
|
|
because its role is classified from its name. There are
|
|
pre-defined standard control names. The details are described in
|
|
the <link linkend="control-interface-control-names"><citetitle>
|
|
Control Names</citetitle></link> subsection.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>index</structfield> field holds the index number
|
|
of this control. If there are several different controls with
|
|
the same name, they can be distinguished by the index
|
|
number. This is the case when
|
|
several codecs exist on the card. If the index is zero, you can
|
|
omit the definition above.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>access</structfield> field contains the access
|
|
type of this control. Give the combination of bit masks,
|
|
<constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there.
|
|
The details will be explained in
|
|
the <link linkend="control-interface-access-flags"><citetitle>
|
|
Access Flags</citetitle></link> subsection.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>private_value</structfield> field contains
|
|
an arbitrary long integer value for this record. When using
|
|
the generic <structfield>info</structfield>,
|
|
<structfield>get</structfield> and
|
|
<structfield>put</structfield> callbacks, you can pass a value
|
|
through this field. If several small numbers are necessary, you can
|
|
combine them in bitwise. Or, it's possible to give a pointer
|
|
(casted to unsigned long) of some record to this field, too.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>tlv</structfield> field can be used to provide
|
|
metadata about the control; see the
|
|
<link linkend="control-interface-tlv">
|
|
<citetitle>Metadata</citetitle></link> subsection.
|
|
</para>
|
|
|
|
<para>
|
|
The other three are
|
|
<link linkend="control-interface-callbacks"><citetitle>
|
|
callback functions</citetitle></link>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-control-names">
|
|
<title>Control Names</title>
|
|
<para>
|
|
There are some standards to define the control names. A
|
|
control is usually defined from the three parts as
|
|
<quote>SOURCE DIRECTION FUNCTION</quote>.
|
|
</para>
|
|
|
|
<para>
|
|
The first, <constant>SOURCE</constant>, specifies the source
|
|
of the control, and is a string such as <quote>Master</quote>,
|
|
<quote>PCM</quote>, <quote>CD</quote> and
|
|
<quote>Line</quote>. There are many pre-defined sources.
|
|
</para>
|
|
|
|
<para>
|
|
The second, <constant>DIRECTION</constant>, is one of the
|
|
following strings according to the direction of the control:
|
|
<quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass
|
|
Playback</quote> and <quote>Bypass Capture</quote>. Or, it can
|
|
be omitted, meaning both playback and capture directions.
|
|
</para>
|
|
|
|
<para>
|
|
The third, <constant>FUNCTION</constant>, is one of the
|
|
following strings according to the function of the control:
|
|
<quote>Switch</quote>, <quote>Volume</quote> and
|
|
<quote>Route</quote>.
|
|
</para>
|
|
|
|
<para>
|
|
The example of control names are, thus, <quote>Master Capture
|
|
Switch</quote> or <quote>PCM Playback Volume</quote>.
|
|
</para>
|
|
|
|
<para>
|
|
There are some exceptions:
|
|
</para>
|
|
|
|
<section id="control-interface-control-names-global">
|
|
<title>Global capture and playback</title>
|
|
<para>
|
|
<quote>Capture Source</quote>, <quote>Capture Switch</quote>
|
|
and <quote>Capture Volume</quote> are used for the global
|
|
capture (input) source, switch and volume. Similarly,
|
|
<quote>Playback Switch</quote> and <quote>Playback
|
|
Volume</quote> are used for the global output gain switch and
|
|
volume.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-control-names-tone">
|
|
<title>Tone-controls</title>
|
|
<para>
|
|
tone-control switch and volumes are specified like
|
|
<quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control -
|
|
Switch</quote>, <quote>Tone Control - Bass</quote>,
|
|
<quote>Tone Control - Center</quote>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-control-names-3d">
|
|
<title>3D controls</title>
|
|
<para>
|
|
3D-control switches and volumes are specified like <quote>3D
|
|
Control - XXX</quote>, e.g. <quote>3D Control -
|
|
Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D
|
|
Control - Space</quote>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-control-names-mic">
|
|
<title>Mic boost</title>
|
|
<para>
|
|
Mic-boost switch is set as <quote>Mic Boost</quote> or
|
|
<quote>Mic Boost (6dB)</quote>.
|
|
</para>
|
|
|
|
<para>
|
|
More precise information can be found in
|
|
<filename>Documentation/sound/alsa/ControlNames.txt</filename>.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="control-interface-access-flags">
|
|
<title>Access Flags</title>
|
|
|
|
<para>
|
|
The access flag is the bitmask which specifies the access type
|
|
of the given control. The default access type is
|
|
<constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>,
|
|
which means both read and write are allowed to this control.
|
|
When the access flag is omitted (i.e. = 0), it is
|
|
considered as <constant>READWRITE</constant> access as default.
|
|
</para>
|
|
|
|
<para>
|
|
When the control is read-only, pass
|
|
<constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead.
|
|
In this case, you don't have to define
|
|
the <structfield>put</structfield> callback.
|
|
Similarly, when the control is write-only (although it's a rare
|
|
case), you can use the <constant>WRITE</constant> flag instead, and
|
|
you don't need the <structfield>get</structfield> callback.
|
|
</para>
|
|
|
|
<para>
|
|
If the control value changes frequently (e.g. the VU meter),
|
|
<constant>VOLATILE</constant> flag should be given. This means
|
|
that the control may be changed without
|
|
<link linkend="control-interface-change-notification"><citetitle>
|
|
notification</citetitle></link>. Applications should poll such
|
|
a control constantly.
|
|
</para>
|
|
|
|
<para>
|
|
When the control is inactive, set
|
|
the <constant>INACTIVE</constant> flag, too.
|
|
There are <constant>LOCK</constant> and
|
|
<constant>OWNER</constant> flags to change the write
|
|
permissions.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section id="control-interface-callbacks">
|
|
<title>Callbacks</title>
|
|
|
|
<section id="control-interface-callbacks-info">
|
|
<title>info callback</title>
|
|
<para>
|
|
The <structfield>info</structfield> callback is used to get
|
|
detailed information on this control. This must store the
|
|
values of the given struct <structname>snd_ctl_elem_info</structname>
|
|
object. For example, for a boolean control with a single
|
|
element:
|
|
|
|
<example>
|
|
<title>Example of info callback</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol,
|
|
struct snd_ctl_elem_info *uinfo)
|
|
{
|
|
uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
|
|
uinfo->count = 1;
|
|
uinfo->value.integer.min = 0;
|
|
uinfo->value.integer.max = 1;
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>type</structfield> field specifies the type
|
|
of the control. There are <constant>BOOLEAN</constant>,
|
|
<constant>INTEGER</constant>, <constant>ENUMERATED</constant>,
|
|
<constant>BYTES</constant>, <constant>IEC958</constant> and
|
|
<constant>INTEGER64</constant>. The
|
|
<structfield>count</structfield> field specifies the
|
|
number of elements in this control. For example, a stereo
|
|
volume would have count = 2. The
|
|
<structfield>value</structfield> field is a union, and
|
|
the values stored are depending on the type. The boolean and
|
|
integer types are identical.
|
|
</para>
|
|
|
|
<para>
|
|
The enumerated type is a bit different from others. You'll
|
|
need to set the string for the currently given item index.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
|
|
struct snd_ctl_elem_info *uinfo)
|
|
{
|
|
static char *texts[4] = {
|
|
"First", "Second", "Third", "Fourth"
|
|
};
|
|
uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
|
|
uinfo->count = 1;
|
|
uinfo->value.enumerated.items = 4;
|
|
if (uinfo->value.enumerated.item > 3)
|
|
uinfo->value.enumerated.item = 3;
|
|
strcpy(uinfo->value.enumerated.name,
|
|
texts[uinfo->value.enumerated.item]);
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Some common info callbacks are available for your convenience:
|
|
<function>snd_ctl_boolean_mono_info()</function> and
|
|
<function>snd_ctl_boolean_stereo_info()</function>.
|
|
Obviously, the former is an info callback for a mono channel
|
|
boolean item, just like <function>snd_myctl_mono_info</function>
|
|
above, and the latter is for a stereo channel boolean item.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section id="control-interface-callbacks-get">
|
|
<title>get callback</title>
|
|
|
|
<para>
|
|
This callback is used to read the current value of the
|
|
control and to return to user-space.
|
|
</para>
|
|
|
|
<para>
|
|
For example,
|
|
|
|
<example>
|
|
<title>Example of get callback</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_myctl_get(struct snd_kcontrol *kcontrol,
|
|
struct snd_ctl_elem_value *ucontrol)
|
|
{
|
|
struct mychip *chip = snd_kcontrol_chip(kcontrol);
|
|
ucontrol->value.integer.value[0] = get_some_value(chip);
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>value</structfield> field depends on
|
|
the type of control as well as on the info callback. For example,
|
|
the sb driver uses this field to store the register offset,
|
|
the bit-shift and the bit-mask. The
|
|
<structfield>private_value</structfield> field is set as follows:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
.private_value = reg | (shift << 16) | (mask << 24)
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
and is retrieved in callbacks like
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol,
|
|
struct snd_ctl_elem_value *ucontrol)
|
|
{
|
|
int reg = kcontrol->private_value & 0xff;
|
|
int shift = (kcontrol->private_value >> 16) & 0xff;
|
|
int mask = (kcontrol->private_value >> 24) & 0xff;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
In the <structfield>get</structfield> callback,
|
|
you have to fill all the elements if the
|
|
control has more than one elements,
|
|
i.e. <structfield>count</structfield> > 1.
|
|
In the example above, we filled only one element
|
|
(<structfield>value.integer.value[0]</structfield>) since it's
|
|
assumed as <structfield>count</structfield> = 1.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-callbacks-put">
|
|
<title>put callback</title>
|
|
|
|
<para>
|
|
This callback is used to write a value from user-space.
|
|
</para>
|
|
|
|
<para>
|
|
For example,
|
|
|
|
<example>
|
|
<title>Example of put callback</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_myctl_put(struct snd_kcontrol *kcontrol,
|
|
struct snd_ctl_elem_value *ucontrol)
|
|
{
|
|
struct mychip *chip = snd_kcontrol_chip(kcontrol);
|
|
int changed = 0;
|
|
if (chip->current_value !=
|
|
ucontrol->value.integer.value[0]) {
|
|
change_current_value(chip,
|
|
ucontrol->value.integer.value[0]);
|
|
changed = 1;
|
|
}
|
|
return changed;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
|
|
As seen above, you have to return 1 if the value is
|
|
changed. If the value is not changed, return 0 instead.
|
|
If any fatal error happens, return a negative error code as
|
|
usual.
|
|
</para>
|
|
|
|
<para>
|
|
As in the <structfield>get</structfield> callback,
|
|
when the control has more than one elements,
|
|
all elements must be evaluated in this callback, too.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-callbacks-all">
|
|
<title>Callbacks are not atomic</title>
|
|
<para>
|
|
All these three callbacks are basically not atomic.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="control-interface-constructor">
|
|
<title>Constructor</title>
|
|
<para>
|
|
When everything is ready, finally we can create a new
|
|
control. To create a control, there are two functions to be
|
|
called, <function>snd_ctl_new1()</function> and
|
|
<function>snd_ctl_add()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
In the simplest way, you can do like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
|
|
if (err < 0)
|
|
return err;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where <parameter>my_control</parameter> is the
|
|
struct <structname>snd_kcontrol_new</structname> object defined above, and chip
|
|
is the object pointer to be passed to
|
|
kcontrol->private_data
|
|
which can be referred to in callbacks.
|
|
</para>
|
|
|
|
<para>
|
|
<function>snd_ctl_new1()</function> allocates a new
|
|
<structname>snd_kcontrol</structname> instance,
|
|
and <function>snd_ctl_add</function> assigns the given
|
|
control component to the card.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-change-notification">
|
|
<title>Change Notification</title>
|
|
<para>
|
|
If you need to change and update a control in the interrupt
|
|
routine, you can call <function>snd_ctl_notify()</function>. For
|
|
example,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
This function takes the card pointer, the event-mask, and the
|
|
control id pointer for the notification. The event-mask
|
|
specifies the types of notification, for example, in the above
|
|
example, the change of control values is notified.
|
|
The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname>
|
|
to be notified.
|
|
You can find some examples in <filename>es1938.c</filename> or
|
|
<filename>es1968.c</filename> for hardware volume interrupts.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="control-interface-tlv">
|
|
<title>Metadata</title>
|
|
<para>
|
|
To provide information about the dB values of a mixer control, use
|
|
on of the <constant>DECLARE_TLV_xxx</constant> macros from
|
|
<filename><sound/tlv.h></filename> to define a variable
|
|
containing this information, set the<structfield>tlv.p
|
|
</structfield> field to point to this variable, and include the
|
|
<constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
|
|
<structfield>access</structfield> field; like this:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
|
|
|
|
static struct snd_kcontrol_new my_control = {
|
|
...
|
|
.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
|
|
SNDRV_CTL_ELEM_ACCESS_TLV_READ,
|
|
...
|
|
.tlv.p = db_scale_my_control,
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The <function>DECLARE_TLV_DB_SCALE</function> macro defines
|
|
information about a mixer control where each step in the control's
|
|
value changes the dB value by a constant dB amount.
|
|
The first parameter is the name of the variable to be defined.
|
|
The second parameter is the minimum value, in units of 0.01 dB.
|
|
The third parameter is the step size, in units of 0.01 dB.
|
|
Set the fourth parameter to 1 if the minimum value actually mutes
|
|
the control.
|
|
</para>
|
|
|
|
<para>
|
|
The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
|
|
information about a mixer control where the control's value affects
|
|
the output linearly.
|
|
The first parameter is the name of the variable to be defined.
|
|
The second parameter is the minimum value, in units of 0.01 dB.
|
|
The third parameter is the maximum value, in units of 0.01 dB.
|
|
If the minimum value mutes the control, set the second parameter to
|
|
<constant>TLV_DB_GAIN_MUTE</constant>.
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- API for AC97 Codec -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="api-ac97">
|
|
<title>API for AC97 Codec</title>
|
|
|
|
<section>
|
|
<title>General</title>
|
|
<para>
|
|
The ALSA AC97 codec layer is a well-defined one, and you don't
|
|
have to write much code to control it. Only low-level control
|
|
routines are necessary. The AC97 codec API is defined in
|
|
<filename><sound/ac97_codec.h></filename>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-example">
|
|
<title>Full Code Example</title>
|
|
<para>
|
|
<example>
|
|
<title>Example of AC97 Interface</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mychip {
|
|
....
|
|
struct snd_ac97 *ac97;
|
|
....
|
|
};
|
|
|
|
static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
|
|
unsigned short reg)
|
|
{
|
|
struct mychip *chip = ac97->private_data;
|
|
....
|
|
/* read a register value here from the codec */
|
|
return the_register_value;
|
|
}
|
|
|
|
static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
|
|
unsigned short reg, unsigned short val)
|
|
{
|
|
struct mychip *chip = ac97->private_data;
|
|
....
|
|
/* write the given register value to the codec */
|
|
}
|
|
|
|
static int snd_mychip_ac97(struct mychip *chip)
|
|
{
|
|
struct snd_ac97_bus *bus;
|
|
struct snd_ac97_template ac97;
|
|
int err;
|
|
static struct snd_ac97_bus_ops ops = {
|
|
.write = snd_mychip_ac97_write,
|
|
.read = snd_mychip_ac97_read,
|
|
};
|
|
|
|
err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
|
|
if (err < 0)
|
|
return err;
|
|
memset(&ac97, 0, sizeof(ac97));
|
|
ac97.private_data = chip;
|
|
return snd_ac97_mixer(bus, &ac97, &chip->ac97);
|
|
}
|
|
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-constructor">
|
|
<title>Constructor</title>
|
|
<para>
|
|
To create an ac97 instance, first call <function>snd_ac97_bus</function>
|
|
with an <type>ac97_bus_ops_t</type> record with callback functions.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_ac97_bus *bus;
|
|
static struct snd_ac97_bus_ops ops = {
|
|
.write = snd_mychip_ac97_write,
|
|
.read = snd_mychip_ac97_read,
|
|
};
|
|
|
|
snd_ac97_bus(card, 0, &ops, NULL, &pbus);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
The bus record is shared among all belonging ac97 instances.
|
|
</para>
|
|
|
|
<para>
|
|
And then call <function>snd_ac97_mixer()</function> with an
|
|
struct <structname>snd_ac97_template</structname>
|
|
record together with the bus pointer created above.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_ac97_template ac97;
|
|
int err;
|
|
|
|
memset(&ac97, 0, sizeof(ac97));
|
|
ac97.private_data = chip;
|
|
snd_ac97_mixer(bus, &ac97, &chip->ac97);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where chip->ac97 is a pointer to a newly created
|
|
<type>ac97_t</type> instance.
|
|
In this case, the chip pointer is set as the private data, so that
|
|
the read/write callback functions can refer to this chip instance.
|
|
This instance is not necessarily stored in the chip
|
|
record. If you need to change the register values from the
|
|
driver, or need the suspend/resume of ac97 codecs, keep this
|
|
pointer to pass to the corresponding functions.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-callbacks">
|
|
<title>Callbacks</title>
|
|
<para>
|
|
The standard callbacks are <structfield>read</structfield> and
|
|
<structfield>write</structfield>. Obviously they
|
|
correspond to the functions for read and write accesses to the
|
|
hardware low-level codes.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>read</structfield> callback returns the
|
|
register value specified in the argument.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
|
|
unsigned short reg)
|
|
{
|
|
struct mychip *chip = ac97->private_data;
|
|
....
|
|
return the_register_value;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
Here, the chip can be cast from ac97->private_data.
|
|
</para>
|
|
|
|
<para>
|
|
Meanwhile, the <structfield>write</structfield> callback is
|
|
used to set the register value.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
|
|
unsigned short reg, unsigned short val)
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
These callbacks are non-atomic like the control API callbacks.
|
|
</para>
|
|
|
|
<para>
|
|
There are also other callbacks:
|
|
<structfield>reset</structfield>,
|
|
<structfield>wait</structfield> and
|
|
<structfield>init</structfield>.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>reset</structfield> callback is used to reset
|
|
the codec. If the chip requires a special kind of reset, you can
|
|
define this callback.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>wait</structfield> callback is used to
|
|
add some waiting time in the standard initialization of the codec. If the
|
|
chip requires the extra waiting time, define this callback.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>init</structfield> callback is used for
|
|
additional initialization of the codec.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-updating-registers">
|
|
<title>Updating Registers in The Driver</title>
|
|
<para>
|
|
If you need to access to the codec from the driver, you can
|
|
call the following functions:
|
|
<function>snd_ac97_write()</function>,
|
|
<function>snd_ac97_read()</function>,
|
|
<function>snd_ac97_update()</function> and
|
|
<function>snd_ac97_update_bits()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
Both <function>snd_ac97_write()</function> and
|
|
<function>snd_ac97_update()</function> functions are used to
|
|
set a value to the given register
|
|
(<constant>AC97_XXX</constant>). The difference between them is
|
|
that <function>snd_ac97_update()</function> doesn't write a
|
|
value if the given value has been already set, while
|
|
<function>snd_ac97_write()</function> always rewrites the
|
|
value.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_ac97_write(ac97, AC97_MASTER, 0x8080);
|
|
snd_ac97_update(ac97, AC97_MASTER, 0x8080);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
<function>snd_ac97_read()</function> is used to read the value
|
|
of the given register. For example,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
value = snd_ac97_read(ac97, AC97_MASTER);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
<function>snd_ac97_update_bits()</function> is used to update
|
|
some bits in the given register.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_ac97_update_bits(ac97, reg, mask, value);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Also, there is a function to change the sample rate (of a
|
|
given register such as
|
|
<constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or
|
|
DRA is supported by the codec:
|
|
<function>snd_ac97_set_rate()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The following registers are available to set the rate:
|
|
<constant>AC97_PCM_MIC_ADC_RATE</constant>,
|
|
<constant>AC97_PCM_FRONT_DAC_RATE</constant>,
|
|
<constant>AC97_PCM_LR_ADC_RATE</constant>,
|
|
<constant>AC97_SPDIF</constant>. When
|
|
<constant>AC97_SPDIF</constant> is specified, the register is
|
|
not really changed but the corresponding IEC958 status bits will
|
|
be updated.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-clock-adjustment">
|
|
<title>Clock Adjustment</title>
|
|
<para>
|
|
In some chips, the clock of the codec isn't 48000 but using a
|
|
PCI clock (to save a quartz!). In this case, change the field
|
|
bus->clock to the corresponding
|
|
value. For example, intel8x0
|
|
and es1968 drivers have their own function to read from the clock.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-proc-files">
|
|
<title>Proc Files</title>
|
|
<para>
|
|
The ALSA AC97 interface will create a proc file such as
|
|
<filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and
|
|
<filename>ac97#0-0+regs</filename>. You can refer to these files to
|
|
see the current status and registers of the codec.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="api-ac97-multiple-codecs">
|
|
<title>Multiple Codecs</title>
|
|
<para>
|
|
When there are several codecs on the same card, you need to
|
|
call <function>snd_ac97_mixer()</function> multiple times with
|
|
ac97.num=1 or greater. The <structfield>num</structfield> field
|
|
specifies the codec number.
|
|
</para>
|
|
|
|
<para>
|
|
If you set up multiple codecs, you either need to write
|
|
different callbacks for each codec or check
|
|
ac97->num in the callback routines.
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- MIDI (MPU401-UART) Interface -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="midi-interface">
|
|
<title>MIDI (MPU401-UART) Interface</title>
|
|
|
|
<section id="midi-interface-general">
|
|
<title>General</title>
|
|
<para>
|
|
Many soundcards have built-in MIDI (MPU401-UART)
|
|
interfaces. When the soundcard supports the standard MPU401-UART
|
|
interface, most likely you can use the ALSA MPU401-UART API. The
|
|
MPU401-UART API is defined in
|
|
<filename><sound/mpu401.h></filename>.
|
|
</para>
|
|
|
|
<para>
|
|
Some soundchips have a similar but slightly different
|
|
implementation of mpu401 stuff. For example, emu10k1 has its own
|
|
mpu401 routines.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="midi-interface-constructor">
|
|
<title>Constructor</title>
|
|
<para>
|
|
To create a rawmidi object, call
|
|
<function>snd_mpu401_uart_new()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_rawmidi *rmidi;
|
|
snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
|
|
irq, &rmidi);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The first argument is the card pointer, and the second is the
|
|
index of this component. You can create up to 8 rawmidi
|
|
devices.
|
|
</para>
|
|
|
|
<para>
|
|
The third argument is the type of the hardware,
|
|
<constant>MPU401_HW_XXX</constant>. If it's not a special one,
|
|
you can use <constant>MPU401_HW_MPU401</constant>.
|
|
</para>
|
|
|
|
<para>
|
|
The 4th argument is the I/O port address. Many
|
|
backward-compatible MPU401 have an I/O port such as 0x330. Or, it
|
|
might be a part of its own PCI I/O region. It depends on the
|
|
chip design.
|
|
</para>
|
|
|
|
<para>
|
|
The 5th argument is a bitflag for additional information.
|
|
When the I/O port address above is part of the PCI I/O
|
|
region, the MPU401 I/O port might have been already allocated
|
|
(reserved) by the driver itself. In such a case, pass a bit flag
|
|
<constant>MPU401_INFO_INTEGRATED</constant>,
|
|
and the mpu401-uart layer will allocate the I/O ports by itself.
|
|
</para>
|
|
|
|
<para>
|
|
When the controller supports only the input or output MIDI stream,
|
|
pass the <constant>MPU401_INFO_INPUT</constant> or
|
|
<constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively.
|
|
Then the rawmidi instance is created as a single stream.
|
|
</para>
|
|
|
|
<para>
|
|
<constant>MPU401_INFO_MMIO</constant> bitflag is used to change
|
|
the access method to MMIO (via readb and writeb) instead of
|
|
iob and outb. In this case, you have to pass the iomapped address
|
|
to <function>snd_mpu401_uart_new()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output
|
|
stream isn't checked in the default interrupt handler. The driver
|
|
needs to call <function>snd_mpu401_uart_interrupt_tx()</function>
|
|
by itself to start processing the output stream in the irq handler.
|
|
</para>
|
|
|
|
<para>
|
|
If the MPU-401 interface shares its interrupt with the other logical
|
|
devices on the card, set <constant>MPU401_INFO_IRQ_HOOK</constant>
|
|
(see <link linkend="midi-interface-interrupt-handler"><citetitle>
|
|
below</citetitle></link>).
|
|
</para>
|
|
|
|
<para>
|
|
Usually, the port address corresponds to the command port and
|
|
port + 1 corresponds to the data port. If not, you may change
|
|
the <structfield>cport</structfield> field of
|
|
struct <structname>snd_mpu401</structname> manually
|
|
afterward. However, <structname>snd_mpu401</structname> pointer is not
|
|
returned explicitly by
|
|
<function>snd_mpu401_uart_new()</function>. You need to cast
|
|
rmidi->private_data to
|
|
<structname>snd_mpu401</structname> explicitly,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_mpu401 *mpu;
|
|
mpu = rmidi->private_data;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
and reset the cport as you like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
mpu->cport = my_own_control_port;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The 6th argument specifies the ISA irq number that will be
|
|
allocated. If no interrupt is to be allocated (because your
|
|
code is already allocating a shared interrupt, or because the
|
|
device does not use interrupts), pass -1 instead.
|
|
For a MPU-401 device without an interrupt, a polling timer
|
|
will be used instead.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="midi-interface-interrupt-handler">
|
|
<title>Interrupt Handler</title>
|
|
<para>
|
|
When the interrupt is allocated in
|
|
<function>snd_mpu401_uart_new()</function>, an exclusive ISA
|
|
interrupt handler is automatically used, hence you don't have
|
|
anything else to do than creating the mpu401 stuff. Otherwise, you
|
|
have to set <constant>MPU401_INFO_IRQ_HOOK</constant>, and call
|
|
<function>snd_mpu401_uart_interrupt()</function> explicitly from your
|
|
own interrupt handler when it has determined that a UART interrupt
|
|
has occurred.
|
|
</para>
|
|
|
|
<para>
|
|
In this case, you need to pass the private_data of the
|
|
returned rawmidi object from
|
|
<function>snd_mpu401_uart_new()</function> as the second
|
|
argument of <function>snd_mpu401_uart_interrupt()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- RawMIDI Interface -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="rawmidi-interface">
|
|
<title>RawMIDI Interface</title>
|
|
|
|
<section id="rawmidi-interface-overview">
|
|
<title>Overview</title>
|
|
|
|
<para>
|
|
The raw MIDI interface is used for hardware MIDI ports that can
|
|
be accessed as a byte stream. It is not used for synthesizer
|
|
chips that do not directly understand MIDI.
|
|
</para>
|
|
|
|
<para>
|
|
ALSA handles file and buffer management. All you have to do is
|
|
to write some code to move data between the buffer and the
|
|
hardware.
|
|
</para>
|
|
|
|
<para>
|
|
The rawmidi API is defined in
|
|
<filename><sound/rawmidi.h></filename>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-constructor">
|
|
<title>Constructor</title>
|
|
|
|
<para>
|
|
To create a rawmidi device, call the
|
|
<function>snd_rawmidi_new</function> function:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_rawmidi *rmidi;
|
|
err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
|
|
if (err < 0)
|
|
return err;
|
|
rmidi->private_data = chip;
|
|
strcpy(rmidi->name, "My MIDI");
|
|
rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
|
|
SNDRV_RAWMIDI_INFO_INPUT |
|
|
SNDRV_RAWMIDI_INFO_DUPLEX;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The first argument is the card pointer, the second argument is
|
|
the ID string.
|
|
</para>
|
|
|
|
<para>
|
|
The third argument is the index of this component. You can
|
|
create up to 8 rawmidi devices.
|
|
</para>
|
|
|
|
<para>
|
|
The fourth and fifth arguments are the number of output and
|
|
input substreams, respectively, of this device (a substream is
|
|
the equivalent of a MIDI port).
|
|
</para>
|
|
|
|
<para>
|
|
Set the <structfield>info_flags</structfield> field to specify
|
|
the capabilities of the device.
|
|
Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is
|
|
at least one output port,
|
|
<constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at
|
|
least one input port,
|
|
and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device
|
|
can handle output and input at the same time.
|
|
</para>
|
|
|
|
<para>
|
|
After the rawmidi device is created, you need to set the
|
|
operators (callbacks) for each substream. There are helper
|
|
functions to set the operators for all the substreams of a device:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
|
|
snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The operators are usually defined like this:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_rawmidi_ops snd_mymidi_output_ops = {
|
|
.open = snd_mymidi_output_open,
|
|
.close = snd_mymidi_output_close,
|
|
.trigger = snd_mymidi_output_trigger,
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
These callbacks are explained in the <link
|
|
linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link>
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
If there are more than one substream, you should give a
|
|
unique name to each of them:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_rawmidi_substream *substream;
|
|
list_for_each_entry(substream,
|
|
&rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
|
|
list {
|
|
sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
|
|
}
|
|
/* same for SNDRV_RAWMIDI_STREAM_INPUT */
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-callbacks">
|
|
<title>Callbacks</title>
|
|
|
|
<para>
|
|
In all the callbacks, the private data that you've set for the
|
|
rawmidi device can be accessed as
|
|
substream->rmidi->private_data.
|
|
<!-- <code> isn't available before DocBook 4.3 -->
|
|
</para>
|
|
|
|
<para>
|
|
If there is more than one port, your callbacks can determine the
|
|
port index from the struct snd_rawmidi_substream data passed to each
|
|
callback:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_rawmidi_substream *substream;
|
|
int index = substream->number;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<section id="rawmidi-interface-op-open">
|
|
<title><function>open</function> callback</title>
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_open(struct snd_rawmidi_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<para>
|
|
This is called when a substream is opened.
|
|
You can initialize the hardware here, but you shouldn't
|
|
start transmitting/receiving data yet.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-op-close">
|
|
<title><function>close</function> callback</title>
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_xxx_close(struct snd_rawmidi_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<para>
|
|
Guess what.
|
|
</para>
|
|
|
|
<para>
|
|
The <function>open</function> and <function>close</function>
|
|
callbacks of a rawmidi device are serialized with a mutex,
|
|
and can sleep.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-op-trigger-out">
|
|
<title><function>trigger</function> callback for output
|
|
substreams</title>
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<para>
|
|
This is called with a nonzero <parameter>up</parameter>
|
|
parameter when there is some data in the substream buffer that
|
|
must be transmitted.
|
|
</para>
|
|
|
|
<para>
|
|
To read data from the buffer, call
|
|
<function>snd_rawmidi_transmit_peek</function>. It will
|
|
return the number of bytes that have been read; this will be
|
|
less than the number of bytes requested when there are no more
|
|
data in the buffer.
|
|
After the data have been transmitted successfully, call
|
|
<function>snd_rawmidi_transmit_ack</function> to remove the
|
|
data from the substream buffer:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
unsigned char data;
|
|
while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
|
|
if (snd_mychip_try_to_transmit(data))
|
|
snd_rawmidi_transmit_ack(substream, 1);
|
|
else
|
|
break; /* hardware FIFO full */
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
If you know beforehand that the hardware will accept data, you
|
|
can use the <function>snd_rawmidi_transmit</function> function
|
|
which reads some data and removes them from the buffer at once:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
while (snd_mychip_transmit_possible()) {
|
|
unsigned char data;
|
|
if (snd_rawmidi_transmit(substream, &data, 1) != 1)
|
|
break; /* no more data */
|
|
snd_mychip_transmit(data);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
If you know beforehand how many bytes you can accept, you can
|
|
use a buffer size greater than one with the
|
|
<function>snd_rawmidi_transmit*</function> functions.
|
|
</para>
|
|
|
|
<para>
|
|
The <function>trigger</function> callback must not sleep. If
|
|
the hardware FIFO is full before the substream buffer has been
|
|
emptied, you have to continue transmitting data later, either
|
|
in an interrupt handler, or with a timer if the hardware
|
|
doesn't have a MIDI transmit interrupt.
|
|
</para>
|
|
|
|
<para>
|
|
The <function>trigger</function> callback is called with a
|
|
zero <parameter>up</parameter> parameter when the transmission
|
|
of data should be aborted.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-op-trigger-in">
|
|
<title><function>trigger</function> callback for input
|
|
substreams</title>
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<para>
|
|
This is called with a nonzero <parameter>up</parameter>
|
|
parameter to enable receiving data, or with a zero
|
|
<parameter>up</parameter> parameter do disable receiving data.
|
|
</para>
|
|
|
|
<para>
|
|
The <function>trigger</function> callback must not sleep; the
|
|
actual reading of data from the device is usually done in an
|
|
interrupt handler.
|
|
</para>
|
|
|
|
<para>
|
|
When data reception is enabled, your interrupt handler should
|
|
call <function>snd_rawmidi_receive</function> for all received
|
|
data:
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
void snd_mychip_midi_interrupt(...)
|
|
{
|
|
while (mychip_midi_available()) {
|
|
unsigned char data;
|
|
data = mychip_midi_read();
|
|
snd_rawmidi_receive(substream, &data, 1);
|
|
}
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
<section id="rawmidi-interface-op-drain">
|
|
<title><function>drain</function> callback</title>
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
<para>
|
|
This is only used with output substreams. This function should wait
|
|
until all data read from the substream buffer have been transmitted.
|
|
This ensures that the device can be closed and the driver unloaded
|
|
without losing data.
|
|
</para>
|
|
|
|
<para>
|
|
This callback is optional. If you do not set
|
|
<structfield>drain</structfield> in the struct snd_rawmidi_ops
|
|
structure, ALSA will simply wait for 50 milliseconds
|
|
instead.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Miscellaneous Devices -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="misc-devices">
|
|
<title>Miscellaneous Devices</title>
|
|
|
|
<section id="misc-devices-opl3">
|
|
<title>FM OPL3</title>
|
|
<para>
|
|
The FM OPL3 is still used in many chips (mainly for backward
|
|
compatibility). ALSA has a nice OPL3 FM control layer, too. The
|
|
OPL3 API is defined in
|
|
<filename><sound/opl3.h></filename>.
|
|
</para>
|
|
|
|
<para>
|
|
FM registers can be directly accessed through the direct-FM API,
|
|
defined in <filename><sound/asound_fm.h></filename>. In
|
|
ALSA native mode, FM registers are accessed through
|
|
the Hardware-Dependent Device direct-FM extension API, whereas in
|
|
OSS compatible mode, FM registers can be accessed with the OSS
|
|
direct-FM compatible API in <filename>/dev/dmfmX</filename> device.
|
|
</para>
|
|
|
|
<para>
|
|
To create the OPL3 component, you have two functions to
|
|
call. The first one is a constructor for the <type>opl3_t</type>
|
|
instance.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_opl3 *opl3;
|
|
snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX,
|
|
integrated, &opl3);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The first argument is the card pointer, the second one is the
|
|
left port address, and the third is the right port address. In
|
|
most cases, the right port is placed at the left port + 2.
|
|
</para>
|
|
|
|
<para>
|
|
The fourth argument is the hardware type.
|
|
</para>
|
|
|
|
<para>
|
|
When the left and right ports have been already allocated by
|
|
the card driver, pass non-zero to the fifth argument
|
|
(<parameter>integrated</parameter>). Otherwise, the opl3 module will
|
|
allocate the specified ports by itself.
|
|
</para>
|
|
|
|
<para>
|
|
When the accessing the hardware requires special method
|
|
instead of the standard I/O access, you can create opl3 instance
|
|
separately with <function>snd_opl3_new()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_opl3 *opl3;
|
|
snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Then set <structfield>command</structfield>,
|
|
<structfield>private_data</structfield> and
|
|
<structfield>private_free</structfield> for the private
|
|
access function, the private data and the destructor.
|
|
The l_port and r_port are not necessarily set. Only the
|
|
command must be set properly. You can retrieve the data
|
|
from the opl3->private_data field.
|
|
</para>
|
|
|
|
<para>
|
|
After creating the opl3 instance via <function>snd_opl3_new()</function>,
|
|
call <function>snd_opl3_init()</function> to initialize the chip to the
|
|
proper state. Note that <function>snd_opl3_create()</function> always
|
|
calls it internally.
|
|
</para>
|
|
|
|
<para>
|
|
If the opl3 instance is created successfully, then create a
|
|
hwdep device for this opl3.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_hwdep *opl3hwdep;
|
|
snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The first argument is the <type>opl3_t</type> instance you
|
|
created, and the second is the index number, usually 0.
|
|
</para>
|
|
|
|
<para>
|
|
The third argument is the index-offset for the sequencer
|
|
client assigned to the OPL3 port. When there is an MPU401-UART,
|
|
give 1 for here (UART always takes 0).
|
|
</para>
|
|
</section>
|
|
|
|
<section id="misc-devices-hardware-dependent">
|
|
<title>Hardware-Dependent Devices</title>
|
|
<para>
|
|
Some chips need user-space access for special
|
|
controls or for loading the micro code. In such a case, you can
|
|
create a hwdep (hardware-dependent) device. The hwdep API is
|
|
defined in <filename><sound/hwdep.h></filename>. You can
|
|
find examples in opl3 driver or
|
|
<filename>isa/sb/sb16_csp.c</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
The creation of the <type>hwdep</type> instance is done via
|
|
<function>snd_hwdep_new()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_hwdep *hw;
|
|
snd_hwdep_new(card, "My HWDEP", 0, &hw);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where the third argument is the index number.
|
|
</para>
|
|
|
|
<para>
|
|
You can then pass any pointer value to the
|
|
<parameter>private_data</parameter>.
|
|
If you assign a private data, you should define the
|
|
destructor, too. The destructor function is set in
|
|
the <structfield>private_free</structfield> field.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
|
|
hw->private_data = p;
|
|
hw->private_free = mydata_free;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
and the implementation of the destructor would be:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void mydata_free(struct snd_hwdep *hw)
|
|
{
|
|
struct mydata *p = hw->private_data;
|
|
kfree(p);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The arbitrary file operations can be defined for this
|
|
instance. The file operators are defined in
|
|
the <parameter>ops</parameter> table. For example, assume that
|
|
this chip needs an ioctl.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
hw->ops.open = mydata_open;
|
|
hw->ops.ioctl = mydata_ioctl;
|
|
hw->ops.release = mydata_release;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
And implement the callback functions as you like.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="misc-devices-IEC958">
|
|
<title>IEC958 (S/PDIF)</title>
|
|
<para>
|
|
Usually the controls for IEC958 devices are implemented via
|
|
the control interface. There is a macro to compose a name string for
|
|
IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function>
|
|
defined in <filename><include/asound.h></filename>.
|
|
</para>
|
|
|
|
<para>
|
|
There are some standard controls for IEC958 status bits. These
|
|
controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>,
|
|
and the size of element is fixed as 4 bytes array
|
|
(value.iec958.status[x]). For the <structfield>info</structfield>
|
|
callback, you don't specify
|
|
the value field for this type (the count field must be set,
|
|
though).
|
|
</para>
|
|
|
|
<para>
|
|
<quote>IEC958 Playback Con Mask</quote> is used to return the
|
|
bit-mask for the IEC958 status bits of consumer mode. Similarly,
|
|
<quote>IEC958 Playback Pro Mask</quote> returns the bitmask for
|
|
professional mode. They are read-only controls, and are defined
|
|
as MIXER controls (iface =
|
|
<constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>).
|
|
</para>
|
|
|
|
<para>
|
|
Meanwhile, <quote>IEC958 Playback Default</quote> control is
|
|
defined for getting and setting the current default IEC958
|
|
bits. Note that this one is usually defined as a PCM control
|
|
(iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>),
|
|
although in some places it's defined as a MIXER control.
|
|
</para>
|
|
|
|
<para>
|
|
In addition, you can define the control switches to
|
|
enable/disable or to set the raw bit mode. The implementation
|
|
will depend on the chip, but the control should be named as
|
|
<quote>IEC958 xxx</quote>, preferably using
|
|
the <function>SNDRV_CTL_NAME_IEC958()</function> macro.
|
|
</para>
|
|
|
|
<para>
|
|
You can find several cases, for example,
|
|
<filename>pci/emu10k1</filename>,
|
|
<filename>pci/ice1712</filename>, or
|
|
<filename>pci/cmipci.c</filename>.
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Buffer and Memory Management -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="buffer-and-memory">
|
|
<title>Buffer and Memory Management</title>
|
|
|
|
<section id="buffer-and-memory-buffer-types">
|
|
<title>Buffer Types</title>
|
|
<para>
|
|
ALSA provides several different buffer allocation functions
|
|
depending on the bus and the architecture. All these have a
|
|
consistent API. The allocation of physically-contiguous pages is
|
|
done via
|
|
<function>snd_malloc_xxx_pages()</function> function, where xxx
|
|
is the bus type.
|
|
</para>
|
|
|
|
<para>
|
|
The allocation of pages with fallback is
|
|
<function>snd_malloc_xxx_pages_fallback()</function>. This
|
|
function tries to allocate the specified pages but if the pages
|
|
are not available, it tries to reduce the page sizes until
|
|
enough space is found.
|
|
</para>
|
|
|
|
<para>
|
|
The release the pages, call
|
|
<function>snd_free_xxx_pages()</function> function.
|
|
</para>
|
|
|
|
<para>
|
|
Usually, ALSA drivers try to allocate and reserve
|
|
a large contiguous physical space
|
|
at the time the module is loaded for the later use.
|
|
This is called <quote>pre-allocation</quote>.
|
|
As already written, you can call the following function at
|
|
pcm instance construction time (in the case of PCI bus).
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
|
|
snd_dma_pci_data(pci), size, max);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where <parameter>size</parameter> is the byte size to be
|
|
pre-allocated and the <parameter>max</parameter> is the maximum
|
|
size to be changed via the <filename>prealloc</filename> proc file.
|
|
The allocator will try to get an area as large as possible
|
|
within the given size.
|
|
</para>
|
|
|
|
<para>
|
|
The second argument (type) and the third argument (device pointer)
|
|
are dependent on the bus.
|
|
In the case of the ISA bus, pass <function>snd_dma_isa_data()</function>
|
|
as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type.
|
|
For the continuous buffer unrelated to the bus can be pre-allocated
|
|
with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the
|
|
<function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer,
|
|
where <constant>GFP_KERNEL</constant> is the kernel allocation flag to
|
|
use.
|
|
For the PCI scatter-gather buffers, use
|
|
<constant>SNDRV_DMA_TYPE_DEV_SG</constant> with
|
|
<function>snd_dma_pci_data(pci)</function>
|
|
(see the
|
|
<link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers
|
|
</citetitle></link> section).
|
|
</para>
|
|
|
|
<para>
|
|
Once the buffer is pre-allocated, you can use the
|
|
allocator in the <structfield>hw_params</structfield> callback:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_pcm_lib_malloc_pages(substream, size);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
Note that you have to pre-allocate to use this function.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="buffer-and-memory-external-hardware">
|
|
<title>External Hardware Buffers</title>
|
|
<para>
|
|
Some chips have their own hardware buffers and the DMA
|
|
transfer from the host memory is not available. In such a case,
|
|
you need to either 1) copy/set the audio data directly to the
|
|
external hardware buffer, or 2) make an intermediate buffer and
|
|
copy/set the data from it to the external hardware buffer in
|
|
interrupts (or in tasklets, preferably).
|
|
</para>
|
|
|
|
<para>
|
|
The first case works fine if the external hardware buffer is large
|
|
enough. This method doesn't need any extra buffers and thus is
|
|
more effective. You need to define the
|
|
<structfield>copy</structfield> and
|
|
<structfield>silence</structfield> callbacks for
|
|
the data transfer. However, there is a drawback: it cannot
|
|
be mmapped. The examples are GUS's GF1 PCM or emu8000's
|
|
wavetable PCM.
|
|
</para>
|
|
|
|
<para>
|
|
The second case allows for mmap on the buffer, although you have
|
|
to handle an interrupt or a tasklet to transfer the data
|
|
from the intermediate buffer to the hardware buffer. You can find an
|
|
example in the vxpocket driver.
|
|
</para>
|
|
|
|
<para>
|
|
Another case is when the chip uses a PCI memory-map
|
|
region for the buffer instead of the host memory. In this case,
|
|
mmap is available only on certain architectures like the Intel one.
|
|
In non-mmap mode, the data cannot be transferred as in the normal
|
|
way. Thus you need to define the <structfield>copy</structfield> and
|
|
<structfield>silence</structfield> callbacks as well,
|
|
as in the cases above. The examples are found in
|
|
<filename>rme32.c</filename> and <filename>rme96.c</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
The implementation of the <structfield>copy</structfield> and
|
|
<structfield>silence</structfield> callbacks depends upon
|
|
whether the hardware supports interleaved or non-interleaved
|
|
samples. The <structfield>copy</structfield> callback is
|
|
defined like below, a bit
|
|
differently depending whether the direction is playback or
|
|
capture:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int playback_copy(struct snd_pcm_substream *substream, int channel,
|
|
snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count);
|
|
static int capture_copy(struct snd_pcm_substream *substream, int channel,
|
|
snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
In the case of interleaved samples, the second argument
|
|
(<parameter>channel</parameter>) is not used. The third argument
|
|
(<parameter>pos</parameter>) points the
|
|
current position offset in frames.
|
|
</para>
|
|
|
|
<para>
|
|
The meaning of the fourth argument is different between
|
|
playback and capture. For playback, it holds the source data
|
|
pointer, and for capture, it's the destination data pointer.
|
|
</para>
|
|
|
|
<para>
|
|
The last argument is the number of frames to be copied.
|
|
</para>
|
|
|
|
<para>
|
|
What you have to do in this callback is again different
|
|
between playback and capture directions. In the
|
|
playback case, you copy the given amount of data
|
|
(<parameter>count</parameter>) at the specified pointer
|
|
(<parameter>src</parameter>) to the specified offset
|
|
(<parameter>pos</parameter>) on the hardware buffer. When
|
|
coded like memcpy-like way, the copy would be like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src,
|
|
frames_to_bytes(runtime, count));
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
For the capture direction, you copy the given amount of
|
|
data (<parameter>count</parameter>) at the specified offset
|
|
(<parameter>pos</parameter>) on the hardware buffer to the
|
|
specified pointer (<parameter>dst</parameter>).
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos),
|
|
frames_to_bytes(runtime, count));
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
Note that both the position and the amount of data are given
|
|
in frames.
|
|
</para>
|
|
|
|
<para>
|
|
In the case of non-interleaved samples, the implementation
|
|
will be a bit more complicated.
|
|
</para>
|
|
|
|
<para>
|
|
You need to check the channel argument, and if it's -1, copy
|
|
the whole channels. Otherwise, you have to copy only the
|
|
specified channel. Please check
|
|
<filename>isa/gus/gus_pcm.c</filename> as an example.
|
|
</para>
|
|
|
|
<para>
|
|
The <structfield>silence</structfield> callback is also
|
|
implemented in a similar way.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int silence(struct snd_pcm_substream *substream, int channel,
|
|
snd_pcm_uframes_t pos, snd_pcm_uframes_t count);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The meanings of arguments are the same as in the
|
|
<structfield>copy</structfield>
|
|
callback, although there is no <parameter>src/dst</parameter>
|
|
argument. In the case of interleaved samples, the channel
|
|
argument has no meaning, as well as on
|
|
<structfield>copy</structfield> callback.
|
|
</para>
|
|
|
|
<para>
|
|
The role of <structfield>silence</structfield> callback is to
|
|
set the given amount
|
|
(<parameter>count</parameter>) of silence data at the
|
|
specified offset (<parameter>pos</parameter>) on the hardware
|
|
buffer. Suppose that the data format is signed (that is, the
|
|
silent-data is 0), and the implementation using a memset-like
|
|
function would be like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0,
|
|
frames_to_bytes(runtime, count));
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
In the case of non-interleaved samples, again, the
|
|
implementation becomes a bit more complicated. See, for example,
|
|
<filename>isa/gus/gus_pcm.c</filename>.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="buffer-and-memory-non-contiguous">
|
|
<title>Non-Contiguous Buffers</title>
|
|
<para>
|
|
If your hardware supports the page table as in emu10k1 or the
|
|
buffer descriptors as in via82xx, you can use the scatter-gather
|
|
(SG) DMA. ALSA provides an interface for handling SG-buffers.
|
|
The API is provided in <filename><sound/pcm.h></filename>.
|
|
</para>
|
|
|
|
<para>
|
|
For creating the SG-buffer handler, call
|
|
<function>snd_pcm_lib_preallocate_pages()</function> or
|
|
<function>snd_pcm_lib_preallocate_pages_for_all()</function>
|
|
with <constant>SNDRV_DMA_TYPE_DEV_SG</constant>
|
|
in the PCM constructor like other PCI pre-allocator.
|
|
You need to pass <function>snd_dma_pci_data(pci)</function>,
|
|
where pci is the struct <structname>pci_dev</structname> pointer
|
|
of the chip as well.
|
|
The <type>struct snd_sg_buf</type> instance is created as
|
|
substream->dma_private. You can cast
|
|
the pointer like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Then call <function>snd_pcm_lib_malloc_pages()</function>
|
|
in the <structfield>hw_params</structfield> callback
|
|
as well as in the case of normal PCI buffer.
|
|
The SG-buffer handler will allocate the non-contiguous kernel
|
|
pages of the given size and map them onto the virtually contiguous
|
|
memory. The virtual pointer is addressed in runtime->dma_area.
|
|
The physical address (runtime->dma_addr) is set to zero,
|
|
because the buffer is physically non-contiguous.
|
|
The physical address table is set up in sgbuf->table.
|
|
You can get the physical address at a certain offset via
|
|
<function>snd_pcm_sgbuf_get_addr()</function>.
|
|
</para>
|
|
|
|
<para>
|
|
When a SG-handler is used, you need to set
|
|
<function>snd_pcm_sgbuf_ops_page</function> as
|
|
the <structfield>page</structfield> callback.
|
|
(See <link linkend="pcm-interface-operators-page-callback">
|
|
<citetitle>page callback section</citetitle></link>.)
|
|
</para>
|
|
|
|
<para>
|
|
To release the data, call
|
|
<function>snd_pcm_lib_free_pages()</function> in the
|
|
<structfield>hw_free</structfield> callback as usual.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="buffer-and-memory-vmalloced">
|
|
<title>Vmalloc'ed Buffers</title>
|
|
<para>
|
|
It's possible to use a buffer allocated via
|
|
<function>vmalloc</function>, for example, for an intermediate
|
|
buffer. Since the allocated pages are not contiguous, you need
|
|
to set the <structfield>page</structfield> callback to obtain
|
|
the physical address at every offset.
|
|
</para>
|
|
|
|
<para>
|
|
The implementation of <structfield>page</structfield> callback
|
|
would be like this:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#include <linux/vmalloc.h>
|
|
|
|
/* get the physical page pointer on the given offset */
|
|
static struct page *mychip_page(struct snd_pcm_substream *substream,
|
|
unsigned long offset)
|
|
{
|
|
void *pageptr = substream->runtime->dma_area + offset;
|
|
return vmalloc_to_page(pageptr);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Proc Interface -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="proc-interface">
|
|
<title>Proc Interface</title>
|
|
<para>
|
|
ALSA provides an easy interface for procfs. The proc files are
|
|
very useful for debugging. I recommend you set up proc files if
|
|
you write a driver and want to get a running status or register
|
|
dumps. The API is found in
|
|
<filename><sound/info.h></filename>.
|
|
</para>
|
|
|
|
<para>
|
|
To create a proc file, call
|
|
<function>snd_card_proc_new()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
struct snd_info_entry *entry;
|
|
int err = snd_card_proc_new(card, "my-file", &entry);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where the second argument specifies the name of the proc file to be
|
|
created. The above example will create a file
|
|
<filename>my-file</filename> under the card directory,
|
|
e.g. <filename>/proc/asound/card0/my-file</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
Like other components, the proc entry created via
|
|
<function>snd_card_proc_new()</function> will be registered and
|
|
released automatically in the card registration and release
|
|
functions.
|
|
</para>
|
|
|
|
<para>
|
|
When the creation is successful, the function stores a new
|
|
instance in the pointer given in the third argument.
|
|
It is initialized as a text proc file for read only. To use
|
|
this proc file as a read-only text file as it is, set the read
|
|
callback with a private data via
|
|
<function>snd_info_set_text_ops()</function>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_info_set_text_ops(entry, chip, my_proc_read);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
where the second argument (<parameter>chip</parameter>) is the
|
|
private data to be used in the callbacks. The third parameter
|
|
specifies the read buffer size and the fourth
|
|
(<parameter>my_proc_read</parameter>) is the callback function, which
|
|
is defined like
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void my_proc_read(struct snd_info_entry *entry,
|
|
struct snd_info_buffer *buffer);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
</para>
|
|
|
|
<para>
|
|
In the read callback, use <function>snd_iprintf()</function> for
|
|
output strings, which works just like normal
|
|
<function>printf()</function>. For example,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static void my_proc_read(struct snd_info_entry *entry,
|
|
struct snd_info_buffer *buffer)
|
|
{
|
|
struct my_chip *chip = entry->private_data;
|
|
|
|
snd_iprintf(buffer, "This is my chip!\n");
|
|
snd_iprintf(buffer, "Port = %ld\n", chip->port);
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The file permissions can be changed afterwards. As default, it's
|
|
set as read only for all users. If you want to add write
|
|
permission for the user (root as default), do as follows:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
and set the write buffer size and the callback
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
entry->c.text.write = my_proc_write;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
For the write callback, you can use
|
|
<function>snd_info_get_line()</function> to get a text line, and
|
|
<function>snd_info_get_str()</function> to retrieve a string from
|
|
the line. Some examples are found in
|
|
<filename>core/oss/mixer_oss.c</filename>, core/oss/and
|
|
<filename>pcm_oss.c</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
For a raw-data proc-file, set the attributes as follows:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct snd_info_entry_ops my_file_io_ops = {
|
|
.read = my_file_io_read,
|
|
};
|
|
|
|
entry->content = SNDRV_INFO_CONTENT_DATA;
|
|
entry->private_data = chip;
|
|
entry->c.ops = &my_file_io_ops;
|
|
entry->size = 4096;
|
|
entry->mode = S_IFREG | S_IRUGO;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
For the raw data, <structfield>size</structfield> field must be
|
|
set properly. This specifies the maximum size of the proc file access.
|
|
</para>
|
|
|
|
<para>
|
|
The read/write callbacks of raw mode are more direct than the text mode.
|
|
You need to use a low-level I/O functions such as
|
|
<function>copy_from/to_user()</function> to transfer the
|
|
data.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static ssize_t my_file_io_read(struct snd_info_entry *entry,
|
|
void *file_private_data,
|
|
struct file *file,
|
|
char *buf,
|
|
size_t count,
|
|
loff_t pos)
|
|
{
|
|
if (copy_to_user(buf, local_data + pos, count))
|
|
return -EFAULT;
|
|
return count;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
If the size of the info entry has been set up properly,
|
|
<structfield>count</structfield> and <structfield>pos</structfield> are
|
|
guaranteed to fit within 0 and the given size.
|
|
You don't have to check the range in the callbacks unless any
|
|
other condition is required.
|
|
|
|
</para>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Power Management -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="power-management">
|
|
<title>Power Management</title>
|
|
<para>
|
|
If the chip is supposed to work with suspend/resume
|
|
functions, you need to add power-management code to the
|
|
driver. The additional code for power-management should be
|
|
<function>ifdef</function>'ed with
|
|
<constant>CONFIG_PM</constant>.
|
|
</para>
|
|
|
|
<para>
|
|
If the driver <emphasis>fully</emphasis> supports suspend/resume
|
|
that is, the device can be
|
|
properly resumed to its state when suspend was called,
|
|
you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag
|
|
in the pcm info field. Usually, this is possible when the
|
|
registers of the chip can be safely saved and restored to
|
|
RAM. If this is set, the trigger callback is called with
|
|
<constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume
|
|
callback completes.
|
|
</para>
|
|
|
|
<para>
|
|
Even if the driver doesn't support PM fully but
|
|
partial suspend/resume is still possible, it's still worthy to
|
|
implement suspend/resume callbacks. In such a case, applications
|
|
would reset the status by calling
|
|
<function>snd_pcm_prepare()</function> and restart the stream
|
|
appropriately. Hence, you can define suspend/resume callbacks
|
|
below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant>
|
|
info flag to the PCM.
|
|
</para>
|
|
|
|
<para>
|
|
Note that the trigger with SUSPEND can always be called when
|
|
<function>snd_pcm_suspend_all</function> is called,
|
|
regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag.
|
|
The <constant>RESUME</constant> flag affects only the behavior
|
|
of <function>snd_pcm_resume()</function>.
|
|
(Thus, in theory,
|
|
<constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed
|
|
to be handled in the trigger callback when no
|
|
<constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But,
|
|
it's better to keep it for compatibility reasons.)
|
|
</para>
|
|
<para>
|
|
In the earlier version of ALSA drivers, a common
|
|
power-management layer was provided, but it has been removed.
|
|
The driver needs to define the suspend/resume hooks according to
|
|
the bus the device is connected to. In the case of PCI drivers, the
|
|
callbacks look like below:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#ifdef CONFIG_PM
|
|
static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
|
|
{
|
|
.... /* do things for suspend */
|
|
return 0;
|
|
}
|
|
static int snd_my_resume(struct pci_dev *pci)
|
|
{
|
|
.... /* do things for suspend */
|
|
return 0;
|
|
}
|
|
#endif
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The scheme of the real suspend job is as follows.
|
|
|
|
<orderedlist>
|
|
<listitem><para>Retrieve the card and the chip data.</para></listitem>
|
|
<listitem><para>Call <function>snd_power_change_state()</function> with
|
|
<constant>SNDRV_CTL_POWER_D3hot</constant> to change the
|
|
power status.</para></listitem>
|
|
<listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem>
|
|
<listitem><para>If AC97 codecs are used, call
|
|
<function>snd_ac97_suspend()</function> for each codec.</para></listitem>
|
|
<listitem><para>Save the register values if necessary.</para></listitem>
|
|
<listitem><para>Stop the hardware if necessary.</para></listitem>
|
|
<listitem><para>Disable the PCI device by calling
|
|
<function>pci_disable_device()</function>. Then, call
|
|
<function>pci_save_state()</function> at last.</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
|
|
<para>
|
|
A typical code would be like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int mychip_suspend(struct pci_dev *pci, pm_message_t state)
|
|
{
|
|
/* (1) */
|
|
struct snd_card *card = pci_get_drvdata(pci);
|
|
struct mychip *chip = card->private_data;
|
|
/* (2) */
|
|
snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
|
|
/* (3) */
|
|
snd_pcm_suspend_all(chip->pcm);
|
|
/* (4) */
|
|
snd_ac97_suspend(chip->ac97);
|
|
/* (5) */
|
|
snd_mychip_save_registers(chip);
|
|
/* (6) */
|
|
snd_mychip_stop_hardware(chip);
|
|
/* (7) */
|
|
pci_disable_device(pci);
|
|
pci_save_state(pci);
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
The scheme of the real resume job is as follows.
|
|
|
|
<orderedlist>
|
|
<listitem><para>Retrieve the card and the chip data.</para></listitem>
|
|
<listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>.
|
|
Then enable the pci device again by calling <function>pci_enable_device()</function>.
|
|
Call <function>pci_set_master()</function> if necessary, too.</para></listitem>
|
|
<listitem><para>Re-initialize the chip.</para></listitem>
|
|
<listitem><para>Restore the saved registers if necessary.</para></listitem>
|
|
<listitem><para>Resume the mixer, e.g. calling
|
|
<function>snd_ac97_resume()</function>.</para></listitem>
|
|
<listitem><para>Restart the hardware (if any).</para></listitem>
|
|
<listitem><para>Call <function>snd_power_change_state()</function> with
|
|
<constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
|
|
<para>
|
|
A typical code would be like:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int mychip_resume(struct pci_dev *pci)
|
|
{
|
|
/* (1) */
|
|
struct snd_card *card = pci_get_drvdata(pci);
|
|
struct mychip *chip = card->private_data;
|
|
/* (2) */
|
|
pci_restore_state(pci);
|
|
pci_enable_device(pci);
|
|
pci_set_master(pci);
|
|
/* (3) */
|
|
snd_mychip_reinit_chip(chip);
|
|
/* (4) */
|
|
snd_mychip_restore_registers(chip);
|
|
/* (5) */
|
|
snd_ac97_resume(chip->ac97);
|
|
/* (6) */
|
|
snd_mychip_restart_chip(chip);
|
|
/* (7) */
|
|
snd_power_change_state(card, SNDRV_CTL_POWER_D0);
|
|
return 0;
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
As shown in the above, it's better to save registers after
|
|
suspending the PCM operations via
|
|
<function>snd_pcm_suspend_all()</function> or
|
|
<function>snd_pcm_suspend()</function>. It means that the PCM
|
|
streams are already stoppped when the register snapshot is
|
|
taken. But, remember that you don't have to restart the PCM
|
|
stream in the resume callback. It'll be restarted via
|
|
trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant>
|
|
when necessary.
|
|
</para>
|
|
|
|
<para>
|
|
OK, we have all callbacks now. Let's set them up. In the
|
|
initialization of the card, make sure that you can get the chip
|
|
data from the card instance, typically via
|
|
<structfield>private_data</structfield> field, in case you
|
|
created the chip data individually.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_mychip_probe(struct pci_dev *pci,
|
|
const struct pci_device_id *pci_id)
|
|
{
|
|
....
|
|
struct snd_card *card;
|
|
struct mychip *chip;
|
|
int err;
|
|
....
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);
|
|
....
|
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL);
|
|
....
|
|
card->private_data = chip;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
When you created the chip data with
|
|
<function>snd_card_create()</function>, it's anyway accessible
|
|
via <structfield>private_data</structfield> field.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int snd_mychip_probe(struct pci_dev *pci,
|
|
const struct pci_device_id *pci_id)
|
|
{
|
|
....
|
|
struct snd_card *card;
|
|
struct mychip *chip;
|
|
int err;
|
|
....
|
|
err = snd_card_create(index[dev], id[dev], THIS_MODULE,
|
|
sizeof(struct mychip), &card);
|
|
....
|
|
chip = card->private_data;
|
|
....
|
|
}
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
</para>
|
|
|
|
<para>
|
|
If you need a space to save the registers, allocate the
|
|
buffer for it here, too, since it would be fatal
|
|
if you cannot allocate a memory in the suspend phase.
|
|
The allocated buffer should be released in the corresponding
|
|
destructor.
|
|
</para>
|
|
|
|
<para>
|
|
And next, set suspend/resume callbacks to the pci_driver.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static struct pci_driver driver = {
|
|
.name = KBUILD_MODNAME,
|
|
.id_table = snd_my_ids,
|
|
.probe = snd_my_probe,
|
|
.remove = snd_my_remove,
|
|
#ifdef CONFIG_PM
|
|
.suspend = snd_my_suspend,
|
|
.resume = snd_my_resume,
|
|
#endif
|
|
};
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Module Parameters -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="module-parameters">
|
|
<title>Module Parameters</title>
|
|
<para>
|
|
There are standard module options for ALSA. At least, each
|
|
module should have the <parameter>index</parameter>,
|
|
<parameter>id</parameter> and <parameter>enable</parameter>
|
|
options.
|
|
</para>
|
|
|
|
<para>
|
|
If the module supports multiple cards (usually up to
|
|
8 = <constant>SNDRV_CARDS</constant> cards), they should be
|
|
arrays. The default initial values are defined already as
|
|
constants for easier programming:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
|
|
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
|
|
static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
If the module supports only a single card, they could be single
|
|
variables, instead. <parameter>enable</parameter> option is not
|
|
always necessary in this case, but it would be better to have a
|
|
dummy option for compatibility.
|
|
</para>
|
|
|
|
<para>
|
|
The module parameters must be declared with the standard
|
|
<function>module_param()()</function>,
|
|
<function>module_param_array()()</function> and
|
|
<function>MODULE_PARM_DESC()</function> macros.
|
|
</para>
|
|
|
|
<para>
|
|
The typical coding would be like below:
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
#define CARD_NAME "My Chip"
|
|
|
|
module_param_array(index, int, NULL, 0444);
|
|
MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
|
|
module_param_array(id, charp, NULL, 0444);
|
|
MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
|
|
module_param_array(enable, bool, NULL, 0444);
|
|
MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
Also, don't forget to define the module description, classes,
|
|
license and devices. Especially, the recent modprobe requires to
|
|
define the module license as GPL, etc., otherwise the system is
|
|
shown as <quote>tainted</quote>.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
MODULE_DESCRIPTION("My Chip");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- How To Put Your Driver -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="how-to-put-your-driver">
|
|
<title>How To Put Your Driver Into ALSA Tree</title>
|
|
<section>
|
|
<title>General</title>
|
|
<para>
|
|
So far, you've learned how to write the driver codes.
|
|
And you might have a question now: how to put my own
|
|
driver into the ALSA driver tree?
|
|
Here (finally :) the standard procedure is described briefly.
|
|
</para>
|
|
|
|
<para>
|
|
Suppose that you create a new PCI driver for the card
|
|
<quote>xyz</quote>. The card module name would be
|
|
snd-xyz. The new driver is usually put into the alsa-driver
|
|
tree, <filename>alsa-driver/pci</filename> directory in
|
|
the case of PCI cards.
|
|
Then the driver is evaluated, audited and tested
|
|
by developers and users. After a certain time, the driver
|
|
will go to the alsa-kernel tree (to the corresponding directory,
|
|
such as <filename>alsa-kernel/pci</filename>) and eventually
|
|
will be integrated into the Linux 2.6 tree (the directory would be
|
|
<filename>linux/sound/pci</filename>).
|
|
</para>
|
|
|
|
<para>
|
|
In the following sections, the driver code is supposed
|
|
to be put into alsa-driver tree. The two cases are covered:
|
|
a driver consisting of a single source file and one consisting
|
|
of several source files.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Driver with A Single Source File</title>
|
|
<para>
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
Modify alsa-driver/pci/Makefile
|
|
</para>
|
|
|
|
<para>
|
|
Suppose you have a file xyz.c. Add the following
|
|
two lines
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd-xyz-objs := xyz.o
|
|
obj-$(CONFIG_SND_XYZ) += snd-xyz.o
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Create the Kconfig entry
|
|
</para>
|
|
|
|
<para>
|
|
Add the new entry of Kconfig for your xyz driver.
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
config SND_XYZ
|
|
tristate "Foobar XYZ"
|
|
depends on SND
|
|
select SND_PCM
|
|
help
|
|
Say Y here to include support for Foobar XYZ soundcard.
|
|
|
|
To compile this driver as a module, choose M here: the module
|
|
will be called snd-xyz.
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
the line, select SND_PCM, specifies that the driver xyz supports
|
|
PCM. In addition to SND_PCM, the following components are
|
|
supported for select command:
|
|
SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART,
|
|
SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC.
|
|
Add the select command for each supported component.
|
|
</para>
|
|
|
|
<para>
|
|
Note that some selections imply the lowlevel selections.
|
|
For example, PCM includes TIMER, MPU401_UART includes RAWMIDI,
|
|
AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP.
|
|
You don't need to give the lowlevel selections again.
|
|
</para>
|
|
|
|
<para>
|
|
For the details of Kconfig script, refer to the kbuild
|
|
documentation.
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Run cvscompile script to re-generate the configure script and
|
|
build the whole stuff again.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Drivers with Several Source Files</title>
|
|
<para>
|
|
Suppose that the driver snd-xyz have several source files.
|
|
They are located in the new subdirectory,
|
|
pci/xyz.
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
Add a new directory (<filename>xyz</filename>) in
|
|
<filename>alsa-driver/pci/Makefile</filename> as below
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
obj-$(CONFIG_SND) += xyz/
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Under the directory <filename>xyz</filename>, create a Makefile
|
|
|
|
<example>
|
|
<title>Sample Makefile for a driver xyz</title>
|
|
<programlisting>
|
|
<![CDATA[
|
|
ifndef SND_TOPDIR
|
|
SND_TOPDIR=../..
|
|
endif
|
|
|
|
include $(SND_TOPDIR)/toplevel.config
|
|
include $(SND_TOPDIR)/Makefile.conf
|
|
|
|
snd-xyz-objs := xyz.o abc.o def.o
|
|
|
|
obj-$(CONFIG_SND_XYZ) += snd-xyz.o
|
|
|
|
include $(SND_TOPDIR)/Rules.make
|
|
]]>
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Create the Kconfig entry
|
|
</para>
|
|
|
|
<para>
|
|
This procedure is as same as in the last section.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Run cvscompile script to re-generate the configure script and
|
|
build the whole stuff again.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Useful Functions -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="useful-functions">
|
|
<title>Useful Functions</title>
|
|
|
|
<section id="useful-functions-snd-printk">
|
|
<title><function>snd_printk()</function> and friends</title>
|
|
<para>
|
|
ALSA provides a verbose version of the
|
|
<function>printk()</function> function. If a kernel config
|
|
<constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this
|
|
function prints the given message together with the file name
|
|
and the line of the caller. The <constant>KERN_XXX</constant>
|
|
prefix is processed as
|
|
well as the original <function>printk()</function> does, so it's
|
|
recommended to add this prefix, e.g.
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n");
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
</para>
|
|
|
|
<para>
|
|
There are also <function>printk()</function>'s for
|
|
debugging. <function>snd_printd()</function> can be used for
|
|
general debugging purposes. If
|
|
<constant>CONFIG_SND_DEBUG</constant> is set, this function is
|
|
compiled, and works just like
|
|
<function>snd_printk()</function>. If the ALSA is compiled
|
|
without the debugging flag, it's ignored.
|
|
</para>
|
|
|
|
<para>
|
|
<function>snd_printdd()</function> is compiled in only when
|
|
<constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note
|
|
that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default
|
|
even if you configure the alsa-driver with
|
|
<option>--with-debug=full</option> option. You need to give
|
|
explicitly <option>--with-debug=detect</option> option instead.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="useful-functions-snd-bug">
|
|
<title><function>snd_BUG()</function></title>
|
|
<para>
|
|
It shows the <computeroutput>BUG?</computeroutput> message and
|
|
stack trace as well as <function>snd_BUG_ON</function> at the point.
|
|
It's useful to show that a fatal error happens there.
|
|
</para>
|
|
<para>
|
|
When no debug flag is set, this macro is ignored.
|
|
</para>
|
|
</section>
|
|
|
|
<section id="useful-functions-snd-bug-on">
|
|
<title><function>snd_BUG_ON()</function></title>
|
|
<para>
|
|
<function>snd_BUG_ON()</function> macro is similar with
|
|
<function>WARN_ON()</function> macro. For example,
|
|
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
snd_BUG_ON(!pointer);
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
or it can be used as the condition,
|
|
<informalexample>
|
|
<programlisting>
|
|
<![CDATA[
|
|
if (snd_BUG_ON(non_zero_is_bug))
|
|
return -EINVAL;
|
|
]]>
|
|
</programlisting>
|
|
</informalexample>
|
|
|
|
</para>
|
|
|
|
<para>
|
|
The macro takes an conditional expression to evaluate.
|
|
When <constant>CONFIG_SND_DEBUG</constant>, is set, if the
|
|
expression is non-zero, it shows the warning message such as
|
|
<computeroutput>BUG? (xxx)</computeroutput>
|
|
normally followed by stack trace.
|
|
|
|
In both cases it returns the evaluated value.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
</chapter>
|
|
|
|
|
|
<!-- ****************************************************** -->
|
|
<!-- Acknowledgments -->
|
|
<!-- ****************************************************** -->
|
|
<chapter id="acknowledgments">
|
|
<title>Acknowledgments</title>
|
|
<para>
|
|
I would like to thank Phil Kerr for his help for improvement and
|
|
corrections of this document.
|
|
</para>
|
|
<para>
|
|
Kevin Conder reformatted the original plain-text to the
|
|
DocBook format.
|
|
</para>
|
|
<para>
|
|
Giuliano Pochini corrected typos and contributed the example codes
|
|
in the hardware constraints section.
|
|
</para>
|
|
</chapter>
|
|
</book>
|