Kernel driver `pc87360-fan.o'
=============================

Status: Alpha, untested.

Supported chips:
  * National Semiconductor PC87360, PC87363 and PC87364
    Addresses scanned: none, address read from Super I/O config space
    Datasheets:
	http://www.national.com/pf/PC/PC87360.html
	http://www.national.com/pf/PC/PC87363.html
	http://www.national.com/pf/PC/PC87364.html

Authors: Jean Delvare <khali@linux-fr.org>


Module Parameters
-----------------

None.


Description
-----------

The National Semiconductor PC87360 Super I/O chip contains monitoring and
PWM control circuitry for two fans. The PC87363 chip is similar, and the
PC87364 chip has monitoring and PWM control for a third fan.

Fan rotation speeds are reported in RPM (revolutions 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.

A different alarm is also triggered if the fan speed is too low to be
measured. It is suggested to increase the fan divisor in this case.

PWM values are from 0 to 255.

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.


Limitations
-----------

This driver is read-only at the moment. Since I don't own a supported
chip for testing, and the datasheet suggests that you shouldn't change
values once the monitoring has started (this is normally done by the BIOS
at boot time), I decided to play it safe.
