Fan speed reporting for Asus Strix cards

Discussion in 'MSI AfterBurner Application Development Forum' started by SSovets, Feb 7, 2016.

  1. SSovets

    SSovets New Member

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    I just bought an Asus Strix Radeon R380 and have some problems with Afterburner reading its fan speeds: although the fans are stopped most of the time, Afterburner reports 25% fan speed, never less. The lower limit in fan monitoring is set to 0%. What could be the problem, how can I make it show the true fan speed?

    L.E. There seems to be a problem with the fan speed reading method: when the cards start heating up, Afterburner starts reporting a higher fan speed, although the fan is still not rotating at all, until afterburner shows 30% fan speed, at which point the fan actually starts to rotate, although I don't know if at 30% or not.
     
    Last edited: Feb 7, 2016
  2. SSovets

    SSovets New Member

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    Update: sometimes, I think after long periods of inactivity, Afterburner reports the correct 0% speed, but only for a while, then it reverts to 25 (maybe after the fan spins for a while). I don't understand what the problem is...
     
  3. AlleyViper

    AlleyViper Master Guru

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    I guess you have all the answers in your post. The fans that come with that card might need a pwm signal of about ~30% pwm to start spinning from a dead stop. Else, the voltage supplied will be less than their startup voltage, so even if the bios temp ramp changes pwm from 0 to 25%, it's still not enough for them to start, so you'll need to wait until it reaches ~30% (for a higher temp) to get fans moving.

    This kind of stuff will always happen if the vbios makes it possible to set pwm values under the fan's minimum startup voltage. Probably, what is happening is that up to a certain temperature the pwm value will be 0% for intended silent operation, and that point it'll jump right to 25% and then it'll ramp in linear fashion until the next temperature/pwm pair defined in the table.
    If things were properly done according to supplied fans, the first active value should have been a little higher, to make sure that fans would always start.

    Just try to set manual steps and see how they behave, and how much pwm they need to start. It's possible that they still rotate with a lower pwm % if you start with a higher pwm level, and decrease it in small steps.

    Also, don't think of it as "fan speed", but the range of pwm adjustment. Fan speed is their true rpm reading, and there should be a graphic with those values in the right side of AB.

    If temperatures are under control, don't bother with it. As that 25-30% range where the fan doesn't spin should only be maintained under low load. Else, make a custom fan graph under AB.
     
    Last edited: Feb 16, 2016
  4. SSovets

    SSovets New Member

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    So am I to understand that the fan speed indicator and graph actually show the PWM signal, and not the fan rpm as a percentage of maximum fan speed? But then why would Asus keep the card at 25% PWM signal most of the time, while still dropping to 0 sometimes, if they both mean 0 rpm anyway, as per the 0 db strategy? Because as soon as AB is indicating less than 30% fan speed - in reality the fan is stopped.
     

  5. AlleyViper

    AlleyViper Master Guru

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    Only rely in fan speed as a measure of rpm.
    Vbios and programs that control fans with 4 pins, will do it by adjusting pwm % levels (wich alter how much times per second the 12V signal is "cut", so that it works as a lower voltage).
    Every fan has it's own voltage vs speed response curve and a minimum startup voltage, so pwm % can't always correspond to linearly to fan speed. And if software permits settings that are too low for the fan to start, it can even damage their motors.

    IMHO, that's a mistake on their part. The sudden jump from 0 to 25% in the vbios fan speed table seems like it was intended to go from silent 0% operation, to a pwm value low enough for fans to start and keep working at minimum speed (instead of increasing linearly with 1,2,3,4-25%). But not all fans are created equal, and either your problem will happen on every card, or only in the few that have fans from a batch that can't start at that speed. I don't find it particularly healthy or desirable to supply pwm voltage to a fan that's stopped.


    If a tool like VBE7.0.0.7b is capable to open your vbios, you might take note of it's fan ramp table/graphic (pwm % vs temp). Then, you'll just need to copy it to a custom fan profile in AB, but take care to raise the first point from 25 to your desired 30% to ensure the fans always start.
     
    Last edited: Feb 18, 2016
  6. SSovets

    SSovets New Member

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    Ok, I understand what you mean, fan % speed actually reads and reports the fan PWM signal. So I tried to read the speed in rpm, "Fan tachometer" in AB, but it has an even more strange behavior: whenever the fan stops, AB keeps reporting the last real fan speed. For example if I set it to 40%, it reports 1301+/-3 rpm, but if I set it to 25%, meaning the fan stops, AB continues to show 1266 rpm (exactly, without any of the fluctuations that you normally get when monitoring fan speed). Is it because it can't conceive a stopped fan?
     
  7. AlleyViper

    AlleyViper Master Guru

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    That might happen due to a combination of fan y cable wiring + fan's rpm reporting behavior under too low current + fan controller/monitoring chip in the gfx's way of dealing with lost rpm signal + AB's own.

    As an example, with a AC Twin Turbo plugged on a 4890, in the lower range of rpm of the fans (30-50% something) it starts reporting rpm x2. My DC AP15 Gentle Typhoon fans will even stop reporting rpm when under ~1350rpm in the MB's or FC5 header, even if they can go much lower.
     
    Last edited: Feb 20, 2016

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