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Old 05-09-2009, 04:54 AM   #1
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does my bios prohibit pwm/fan control?


I'm trying to regulate the fans in my VIA A2000 barebone (VIA VX800 chipset) but the mainboard doesn't seem to allow this.

I've already installed the latest kernel (2.6.29-RC4), lm-sensors package (3.10) and ran sensors-detect. It seems that the hardware has been correctly identified and set up:

$ sensors
Adapter: SMBus Via Pro adapter at 0500
in0:         +1.09 V  (min =  +0.00 V, max =  +2.04 V)
in1:         +1.82 V  (min =  +0.00 V, max =  +2.04 V)
in2:         +1.09 V  (min =  +0.00 V, max =  +2.04 V)
fan1:       5037 RPM  (min = 5037 RPM, div = 4)
fan2:       1804 RPM  (min = 1804 RPM, div = 4)
temp1:       +70.0C  (high = +50.0C, hyst = +49.0C)
temp2:       +37.0C  (high = +50.0C, hyst = +49.0C)
But when I try to run pwmconfig, no speed changes occur when adjusting the pwm values and the fans keep rotating at full speed.

Manually echoing values to /sys/class/hwmon/hwmon0/device/pwmX also doesn't affect the fan speed (although the PWM value does change).

After looking at the the sources of the viapro-module, I've seen that the device should also support DC-regulated change of fan speed (pwmX_mode 0 instead of 1). But when I try to set the value to 0, the system accepts it but an immediate reading of the value returns 1 again :-(

What might be the reason? Is it a BIOS related bug or has VIA simply disabled any write-access to the i2c-bus?

Last edited by oxident; 05-09-2009 at 04:55 AM. Reason: w83l786ng, viapro, vx800, fan
Old 05-09-2009, 08:03 PM   #2
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Registered: Jun 2008
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Perhaps a dumb question...

The motherboard has a four pin connection for the CPU fan and the BIOS has a setting where you can specify the type or mode of the CPU fan installed? PWM is a four-pin connection, but you may be able to regulate the fan speed in a three-pin connection by controlling the voltage and have a setting for voltage control. Does the motherboard have at least some setting you might change giving you an indication that the board supports a PWM fan or an automatic adjustment of the fan speed?

You have the motherboard manual or could search and download it for more information? Do you have the latest BIOS installed for the motherboard? It may help.

You posted what linux tells you by command, but mention nothing about what the BIOS enables you, or not, as the case may be.
Old 05-10-2009, 09:37 AM   #3
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Sorry, it seems that I've forgotten to write about these things:

The mainboard's SYS_FAN and CPU_FAN connectors only have 3 pins and so I guess that speed controlling via PWM isn't possible. Unfortunately, VIA's BIOS implementations for embedded boards have always been quite limited and there's neither a direct setting about fan control nor an "abstracted" setting like silent or performance.

So it seems to me that the BIOS (which is the only and latest available) initially configures the Winbond chip to use PWM mode although the connectors only support DC regulated control.


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