Re: fan control

Herbert Nachtnebel
2003-05-02T12:00:45Z

> In this moment:
>
> $ cat /proc/acpi/thermal_zone/TZ1/temperature
> temperature: 50 C
>
> $ cat /proc/acpi/fan/FAN*/state
> status: on
> status: off
> status: off
> status: off

Ah, here it is - correct.

> (I changed the name of the fans to the more readable FAN[0-3], OK?)

:-)

> if I echo -n 3 > /proc/acpi/fan/FAN0/state

> then the fan stops.
> After reaching the second trip point, the fan starts up and I have the
> following status report

You have explicitely turned it off.

> $ cat /proc/acpi/fan/FAN*/state
> status: off
> status: on
> status: off
> status: off
>
> This is what is strange.

Well, not really. ACPI fan (speed) control is a little bit artificial. In your case there are four devices presented to the system which has to be activated or deactivated according to the temprature measured by TZ1. What the system doesn't know is that these four devices are in fact the same and are translated into different rotating speeds of the FAN. To correctly achieve the result you are expect, the acpi subsystem would have to guess that an activated FAN device means that all other FAN devices before that device also are activated. A little bit much guessing, not?

Have a look, if the temperature is dropping again under the second treshold in your above situation than you will see that the state of the devices will be correctly again.

Ciao,
Herbert.