Fix fan speeds on ADM1026
mds at paradyne.com
Thu Jun 12 19:41:18 CEST 2003
doc/fan-divisors also has a good explanation
Philip Pokorny wrote:
> Jean Delvare wrote:
> >>Jerome Hsiao @ Arima pointed out to me that the fan speeds from the
> >>ADM1026 driver were not consistent with other drivers.
> >>Seems that most (all?) drivers assume two pulses per rev from the
> >> I expected that users would need to use a "compute" directive to
> >>modify the fan speed for the number of pulses-per-rev of their fans.
> >>(All the fans I use are 4 ppr so I'm always having to "compute" a
> >>correct value.)
> >>But it's not consistent with the other drives...
> >>So here is a patch to fix the ADM1026 so it reports fan speeds
> >>consistent with the other drivers...
> >>This was done against CVS...
> > Well, that's what fanX_div is meant for. As far as I know, the number of
> > pulse/rotation depends mostly on the fan itself, not on the monitoring
> > chipset. That's why we let the users change the fanX_div value through
> > the config file.
> > Maybe there's actually something to be fixed in the adm1026 driver, but
> > maybe this is just a matter of setting the right fanX_div for unregular
> > fans.
> No, fan_div doesn't work that way in practice.
> Most (all?) drivers include fan_div in the conversion from counts to
> RPM. That means that when you change fan_div the RPM reading stays the
> In practice, changing fan_div affects the minimum detectable fan speed
> and the precision of the measured fan speed.
> With a 22.5kHz clock, and assuming 2 pulse/rev fans, you get the following:
> Min Typ Significant Bits in Count
> Fan Div 254 153 3000 4400 10k 4ppr
> -------- ------ ------ ------ ------ ---------
> 1 2657 4411 7.81 7.26 5.08
> 2 1329 2206 6.81 6.26 4.08
> 4 664 1103 5.81 5.26 3.08
> 8 332 551 4.81 4.26 2.08
> At a fan_div setting of 8, the 10k, 4ppr fan is only gating 4 counts on
> average giving fan readings of: 14063 (3), 10547 (4), 8437 (5)
> depending on how many counts you got that sample. Clearly, you want to
> set the fan_div as low as possible and still detect your fans.
> Philip Pokorny, Director of Engineering
> Tel: 415-358-2635 Fax: 415-358-2646 Toll Free: 888-PENGUIN
> PENGUIN COMPUTING, INC.
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