[ltp] fancontrol script causes hundreds of wakeups per second

[Henrique de Moraes Holschuh]

On Wed, 02 Jul 2008, green wrote:
> Okay.  I guess there is still a problem, even for the T61?  This fan will pulse 
> somewhat if I write to pwm1 too often.  Or maybe the pulsing I notice is less 
> and caused elseway.

1. It pulses when you leave it alone, but it should be the kind of thing you
can only hear if you are in a silent room.  The pulses change the RPM just
enough to make sure the limited tachometer is not giving false readings.
This is needed because the thinkpad does closed-loop speed control on the
fan.

2. Any regular fan under PWM control will "pulse" when you change its RPM,
except if you have an actual 4-wire fan (power, gnd, PWM drive input,
tachometer output), AND you change the PWM duty cycle VERY slowly.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh