I have the via datasheets and other info, the scale factor for the via chips is correct. Philip Pokorny wrote: > Doh... I guess I should RTFM next time... > > A quick grep surprised me. Almost all of the chips use a 22.5kHz clock for > fan sensing. I didn't expect that. The exceptions are: > > 1. The lm85 which has a 16-bit fan counter and 90kHz clock > 2. The SMSC47m1 which has some funky preload thing going on > 3. The VIA VT1211 and VT8231 which use 1310720 instead of 1350000 > > I wonder if the VIA scale factor (2^17 * 10) is a mistake. Does anyone > have a > datasheet for those chips? > > :v) > > Mark Studebaker wrote: > > > 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 > >>>>fans. > >>>> 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 > >>same. > >> > >>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: > >> > >> RPM > >> 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. > >> > >>:v) > >> > >>-- > >>Philip Pokorny, Director of Engineering > >>Tel: 415-358-2635 Fax: 415-358-2646 Toll Free: 888-PENGUIN > >>PENGUIN COMPUTING, INC. > >>www.penguincomputing.com > >> > > > > >
