99 lines
4 KiB
Text
99 lines
4 KiB
Text
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Userspace communication protocol over connector [1].
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Message types.
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=============
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There are three types of messages between w1 core and userspace:
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1. Events. They are generated each time new master or slave device found
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either due to automatic or requested search.
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2. Userspace commands. Includes read/write and search/alarm search comamnds.
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3. Replies to userspace commands.
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Protocol.
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========
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[struct cn_msg] - connector header. It's length field is equal to size of the attached data.
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[struct w1_netlink_msg] - w1 netlink header.
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__u8 type - message type.
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W1_SLAVE_ADD/W1_SLAVE_REMOVE - slave add/remove events.
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W1_MASTER_ADD/W1_MASTER_REMOVE - master add/remove events.
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W1_MASTER_CMD - userspace command for bus master device (search/alarm search).
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W1_SLAVE_CMD - userspace command for slave device (read/write/ search/alarm search
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for bus master device where given slave device found).
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__u8 res - reserved
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__u16 len - size of attached to this header data.
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union {
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__u8 id; - slave unique device id
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struct w1_mst {
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__u32 id; - master's id.
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__u32 res; - reserved
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} mst;
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} id;
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[strucrt w1_netlink_cmd] - command for gived master or slave device.
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__u8 cmd - command opcode.
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W1_CMD_READ - read command.
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W1_CMD_WRITE - write command.
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W1_CMD_SEARCH - search command.
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W1_CMD_ALARM_SEARCH - alarm search command.
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__u8 res - reserved
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__u16 len - length of data for this command.
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For read command data must be allocated like for write command.
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__u8 data[0] - data for this command.
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Each connector message can include one or more w1_netlink_msg with zero of more attached w1_netlink_cmd messages.
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For event messages there are no w1_netlink_cmd embedded structures, only connector header
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and w1_netlink_msg strucutre with "len" field being zero and filled type (one of event types)
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and id - either 8 bytes of slave unique id in host order, or master's id, which is assigned
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to bus master device when it is added to w1 core.
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Currently replies to userspace commands are only generated for read command request.
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One reply is generated exactly for one w1_netlink_cmd read request.
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Replies are not combined when sent - i.e. typical reply messages looks like the following:
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[cn_msg][w1_netlink_msg][w1_netlink_cmd]
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cn_msg.len = sizeof(struct w1_netlink_msg) + sizeof(struct w1_netlink_cmd) + cmd->len;
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w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
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w1_netlink_cmd.len = cmd->len;
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Operation steps in w1 core when new command is received.
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=======================================================
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When new message (w1_netlink_msg) is received w1 core detects if it is master of slave request,
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according to w1_netlink_msg.type field.
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Then master or slave device is searched for.
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When found, master device (requested or those one on where slave device is found) is locked.
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If slave command is requested, then reset/select procedure is started to select given device.
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Then all requested in w1_netlink_msg operations are performed one by one.
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If command requires reply (like read command) it is sent on command completion.
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When all commands (w1_netlink_cmd) are processed muster device is unlocked
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and next w1_netlink_msg header processing started.
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Connector [1] specific documentation.
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====================================
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Each connector message includes two u32 fields as "address".
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w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
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Each message also includes sequence and acknowledge numbers.
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Sequence number for event messages is appropriate bus master sequence number increased with
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each event message sent "through" this master.
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Sequence number for userspace requests is set by userspace application.
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Sequence number for reply is the same as was in request, and
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acknowledge number is set to seq+1.
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Additional documantion, source code examples.
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============================================
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1. Documentation/connector
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2. http://tservice.net.ru/~s0mbre/archive/w1
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This archive includes userspace application w1d.c which
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uses read/write/search commands for all master/slave devices found on the bus.
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