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xianfeng |
Kernel driver lm87
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==================
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Supported chips:
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* National Semiconductor LM87
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Prefix: 'lm87'
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Addresses scanned: I2C 0x2c - 0x2f
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Datasheet: http://www.national.com/pf/LM/LM87.html
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Authors:
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Frodo Looijaard ,
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Philip Edelbrock ,
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Mark Studebaker ,
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Stephen Rousset ,
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Dan Eaton ,
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Jean Delvare ,
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Original 2.6 port Jeff Oliver
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Description
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-----------
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This driver implements support for the National Semiconductor LM87.
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The LM87 implements up to three temperature sensors, up to two fan
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rotation speed sensors, up to seven voltage sensors, alarms, and some
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miscellaneous stuff.
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Temperatures are measured in degrees Celsius. Each input has a high
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and low alarm settings. A high limit produces an alarm when the value
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goes above it, and an alarm is also produced when the value goes below
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the low limit.
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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
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volts. An alarm is triggered if the voltage has crossed a programmable
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minimum or maximum limit. Note that minimum in this case always means
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'closest to zero'; this is important for negative voltage measurements.
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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 1.0 seconds since the last update). This means that you can easily
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miss once-only alarms.
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The lm87 driver only updates its values each 1.0 seconds; reading it more
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often will do no harm, but will return 'old' values.
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Hardware Configurations
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-----------------------
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The LM87 has four pins which can serve one of two possible functions,
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depending on the hardware configuration.
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Some functions share pins, so not all functions are available at the same
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time. Which are depends on the hardware setup. This driver assumes that
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the BIOS configured the chip correctly. In that respect, it differs from
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the original driver (from lm_sensors for Linux 2.4), which would force the
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LM87 to an arbitrary, compile-time chosen mode, regardless of the actual
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chipset wiring.
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For reference, here is the list of exclusive functions:
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- in0+in5 (default) or temp3
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- fan1 (default) or in6
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- fan2 (default) or in7
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- VID lines (default) or IRQ lines (not handled by this driver)
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