Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

Kernel driver lm78

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Supported chips:

  * National Semiconductor LM78 / LM78-J

    Prefix: 'lm78'

    Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)

    Datasheet: Publicly available at the National Semiconductor website

               http://www.national.com/

  * National Semiconductor LM79

    Prefix: 'lm79'

    Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)

    Datasheet: Publicly available at the National Semiconductor website

               http://www.national.com/

Author: Frodo Looijaard 

Description

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This driver implements support for the National Semiconductor LM78, LM78-J

and LM79. They are described as 'Microprocessor System Hardware Monitors'.

There is almost no difference between the three supported chips. Functionally,

the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,

which is used to report the lower voltages newer Pentium processors use.

From here on, LM7* means either of these three types.

The LM7* implements one temperature sensor, three fan rotation speed sensors,

seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.

Temperatures are measured in degrees Celsius. An alarm is triggered once

when the Overtemperature Shutdown limit is crossed; it is triggered again

as soon as it drops below the Hysteresis value. A more useful behavior

can be found by setting the Hysteresis value to +127 degrees Celsius; in

this case, alarms are issued during all the time when the actual temperature

is above the Overtemperature Shutdown value. Measurements are guaranteed

between -55 and +125 degrees, with 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 4.08 volts, with a resolution

of 0.016 volt.

The VID lines encode the core voltage value: the voltage level your processor

should work with. This is hardcoded by the mainboard and/or processor itself.

It is a value in volts. When it is unconnected, you will often find the

value 3.50 V here.

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 1.5 seconds since the last update). This means that you can easily

miss once-only alarms.

The LM7* only updates its values each 1.5 seconds; reading it more often

will do no harm, but will return 'old' values.