57 lines
2.5 KiB
Text
57 lines
2.5 KiB
Text
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Kernel driver lm80
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==================
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Supported chips:
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* National Semiconductor LM80
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Prefix: 'lm80'
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Addresses scanned: I2C 0x28 - 0x2f
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/
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Authors:
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Frodo Looijaard <frodol@dds.nl>,
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Philip Edelbrock <phil@netroedge.com>
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Description
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-----------
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This driver implements support for the National Semiconductor LM80.
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It is described as a 'Serial Interface ACPI-Compatible Microprocessor
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System Hardware Monitor'.
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The LM80 implements one temperature sensor, two fan rotation speed sensors,
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seven voltage sensors, alarms, and some miscellaneous stuff.
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Temperatures are measured in degrees Celsius. There are two sets of limits
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which operate independently. When the HOT Temperature Limit is crossed,
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this will cause an alarm that will be reasserted until the temperature
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drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
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should work in the same way (but this must be checked; the datasheet
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is unclear about this). Measurements are guaranteed between -55 and
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+125 degrees. The current temperature measurement has a resolution of
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0.0625 degrees; the limits have a resolution of 1 degree.
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Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
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triggered if the rotation speed has dropped below a programmable limit. Fan
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readings can be divided by a programmable divider (1, 2, 4 or 8) to give
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the readings more range or accuracy. Not all RPM values can accurately be
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represented, so some rounding is done. With a divider of 2, the lowest
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representable value is around 2600 RPM.
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Voltage sensors (also known as IN sensors) report their values in volts.
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An alarm is triggered if the voltage has crossed a programmable minimum
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or maximum limit. Note that minimum in this case always means 'closest to
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zero'; this is important for negative voltage measurements. All voltage
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inputs can measure voltages between 0 and 2.55 volts, with a resolution
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of 0.01 volt.
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If an alarm triggers, it will remain triggered until the hardware register
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is read at least once. This means that the cause for the alarm may
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already have disappeared! Note that in the current implementation, all
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hardware registers are read whenever any data is read (unless it is less
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than 2.0 seconds since the last update). This means that you can easily
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miss once-only alarms.
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The LM80 only updates its values each 1.5 seconds; reading it more often
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will do no harm, but will return 'old' values.
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