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- Kernel driver lm80
- ==================
- Supported chips:
- * National Semiconductor LM80
- Prefix: 'lm80'
- Addresses scanned: I2C 0x28 - 0x2f
- Datasheet: Publicly available at the National Semiconductor website
- http://www.national.com/
- Authors:
- Frodo Looijaard <frodol@dds.nl>,
- Philip Edelbrock <phil@netroedge.com>
- Description
- -----------
- This driver implements support for the National Semiconductor LM80.
- It is described as a 'Serial Interface ACPI-Compatible Microprocessor
- System Hardware Monitor'.
- The LM80 implements one temperature sensor, two fan rotation speed sensors,
- seven voltage sensors, alarms, and some miscellaneous stuff.
- Temperatures are measured in degrees Celsius. There are two sets of limits
- which operate independently. When the HOT Temperature Limit is crossed,
- this will cause an alarm that will be reasserted until the temperature
- drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
- should work in the same way (but this must be checked; the datasheet
- is unclear about this). Measurements are guaranteed between -55 and
- +125 degrees. The current temperature measurement has a resolution of
- 0.0625 degrees; the limits have a resolution of 1 degree.
- 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. All voltage
- inputs can measure voltages between 0 and 2.55 volts, with a resolution
- of 0.01 volt.
- 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 2.0 seconds since the last update). This means that you can easily
- miss once-only alarms.
- The LM80 only updates its values each 1.5 seconds; reading it more often
- will do no harm, but will return 'old' values.
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