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Diffstat (limited to 'Documentation/i2c/chips/lm87')
| -rw-r--r-- | Documentation/i2c/chips/lm87 | 73 |
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diff --git a/Documentation/i2c/chips/lm87 b/Documentation/i2c/chips/lm87 new file mode 100644 index 000000000000..c952c57f0e11 --- /dev/null +++ b/Documentation/i2c/chips/lm87 @@ -0,0 +1,73 @@ +Kernel driver lm87 +================== + +Supported chips: + * National Semiconductor LM87 + Prefix: 'lm87' + Addresses scanned: I2C 0x2c - 0x2f + Datasheet: http://www.national.com/pf/LM/LM87.html + +Authors: + Frodo Looijaard <frodol@dds.nl>, + Philip Edelbrock <phil@netroedge.com>, + Mark Studebaker <mdsxyz123@yahoo.com>, + Stephen Rousset <stephen.rousset@rocketlogix.com>, + Dan Eaton <dan.eaton@rocketlogix.com>, + Jean Delvare <khali@linux-fr.org>, + Original 2.6 port Jeff Oliver + +Description +----------- + +This driver implements support for the National Semiconductor LM87. + +The LM87 implements up to three temperature sensors, up to two fan +rotation speed sensors, up to seven voltage sensors, alarms, and some +miscellaneous stuff. + +Temperatures are measured in degrees Celsius. Each input has a high +and low alarm settings. A high limit produces an alarm when the value +goes above it, and an alarm is also produced when the value goes below +the low limit. + +Fan rotation speeds are reported in RPM (rotations per minute). An alarm is +triggered if the rotation speed has dropped below a programmable limit. Fan +readings can be divided by a programmable divider (1, 2, 4 or 8) to give +the readings more range or accuracy. Not all RPM values can accurately be +represented, so some rounding is done. With a divider of 2, the lowest +representable value is around 2600 RPM. + +Voltage sensors (also known as IN sensors) report their values in +volts. An alarm is triggered if the voltage has crossed a programmable +minimum or maximum limit. Note that minimum in this case always means +'closest to zero'; this is important for negative voltage measurements. + +If an alarm triggers, it will remain triggered until the hardware register +is read at least once. This means that the cause for the alarm may +already have disappeared! Note that in the current implementation, all +hardware registers are read whenever any data is read (unless it is less +than 1.0 seconds since the last update). This means that you can easily +miss once-only alarms. + +The lm87 driver only updates its values each 1.0 seconds; reading it more +often will do no harm, but will return 'old' values. + + +Hardware Configurations +----------------------- + +The LM87 has four pins which can serve one of two possible functions, +depending on the hardware configuration. + +Some functions share pins, so not all functions are available at the same +time. Which are depends on the hardware setup. This driver assumes that +the BIOS configured the chip correctly. In that respect, it differs from +the original driver (from lm_sensors for Linux 2.4), which would force the +LM87 to an arbitrary, compile-time chosen mode, regardless of the actual +chipset wiring. + +For reference, here is the list of exclusive functions: + - in0+in5 (default) or temp3 + - fan1 (default) or in6 + - fan2 (default) or in7 + - VID lines (default) or IRQ lines (not handled by this driver) |
