Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

Kernel driver lm80

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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 ,

        Philip Edelbrock 

Description

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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.