Newbie question about pwm control

Discussion in 'Overclocking, Cooling & Modding' started by TheApprentice, Sep 11, 2006.

  1. TheApprentice

    TheApprentice Newbie

    Hi guys
    As you can tell from the name I am new here and am in need of some guidance.
    I am not a stranger to bios settings but I am always willing to admit that I need help when I am stuck. I am currently trying to set up the pwm control on my Foxconn(!) mobo, and I don't quite understand a couple of the settings.

    I got a Foxconn 945g7ma mobo (Intel 945 chipset-64 bit compliant), Pentium 4 630 3GHz Hyperthread cpu (emt64) with 4-pin cooling fan (retail package) and 1GHz of ddr2 ram (amongst other thing which don't actually relate to my question here)

    I would like to know if anybody has any guidelines about setting two of the pwm values in the bios.
    1. pwm start value (0~127)
    2. pwm slope value (currently set to 2 pwm/c)

    There are two other settings which relate to the pwm start temperature value and the full-on temperature value, quite straight forward.

    What I cannot seem to achieve is a gradual fan-slope between the two temperatures, the fan is either idling at around 1300 rpm or full-on at around 4560rpm (or constantly start-stopping if the temp. is on the threshold of the full-on temperature). I was wondering if the two settings I mentioned above would allow for a gradual slope (if it is at all possible on this mobo), or whether I am stuck with simple "slow" and "full" control?

    As mentioned, I have a 4-pin fan so I assume that I can have some kind of gradual speed control over the fan.

    Any help would be most gratefully and humbly received at this point.:confused:
  2. TheApprentice

    TheApprentice Newbie

    Just an update here, I have set my pwm start value to 63, which according to MY theroy should start the fan at around half of it's rated speed (around 2300 rpm). BUT when I re-boot it goes right back down to around 1400(?)
    It does kick to full power when it reached the specified "full-on" temp no problems.
    I wonder if I have actually got this linear control capability on this board or whether it is a straight slow/fast switching thing?
  3. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Hmm.. Unfortunately, nope. :(

    I'll need to do some research on this.
  4. TheApprentice

    TheApprentice Newbie

    Thank you, I appreciate the input. A real puzzler this one...
  5. TheApprentice

    TheApprentice Newbie

    Okay, another update on this one
    From around 60% or the total rpm speed upwards, the pwm value will start the cpu fan speed at a value that is approximately the same percentage rate as x/127 (!)
    However setting a value BELOW ~60% of the rpm speed will kick the fan controller down to minimum (~1500 in my case) regardless of the value entered. It seems there is a limitation in the fan controller, it can't control speeds below ~60% of maximum.

    Let me make that a lot clearer - my pwm start value can be set to anything between 0~127. If I set it to 77 then this value represents (77/127)*maxrpmrate. In my case the maxrpmrate is ~4500rpm.

    Using this calculation we get (77/127)*4500. Well 77/127=0.60, multiply this by 100 and we get a percentage of ~60%. If we calculate what 60% of the max 4500rpm would be then we get 2700rpm.

    This is approximately what is happening, providing I set the pwm slope value to 2*pwm value/deg. C (default for my bios). I haven't yet played with this setting but I am assuming it affects the ramp rpm value from pwm start to maximum according to cpu temp. This would allow the rpm to increase in a non-linear ramp for smaller increases in cpu temp.

    If anybody can clarify this then please do, I don't have a degree in maths so I am not very good at explaining this kind of thing. :)
    This works GREAT. I have found the optimum temp settings for my cpu just by listening to the fan rpm. Linear ramping works a treat!
    Last edited: Sep 17, 2006

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