Am 06.11.2011 19:45, schrieb Jean Delvare: > On Sun, 06 Nov 2011 19:03:55 +0100, Soeren D. Schulze wrote: >> It's me with my NCT6776 again. >> >> It doesn't seem to be the driver that is causing problems. >> >> When I force the PWM to full duty cycle at low CPU temperature, I get >> about 2200 RPM. I get the same thing when I disconnect the PWM pin >> completely (so apparently the driver sets the PWM duty cycle correctly). >> Voltage on the supply pin of the fan is 12 V. >> >> When put load on the system and CPU temperature rises, though, the fan >> RPM rise up to 2800. The question is: What is the reason for this RPM >> rise? It can't be the PWM signal, as the PWM pin is disconnected. It >> can't be the voltage, because the voltage stays at 12 V (I measured it). >> >> The only explanation that comes to my mind is that the fan does not >> actually go to full speed even at full PWM duty cycle until it senses >> high temperature itself. This implies that the fan has some integrated >> temperature sensor. >> >> Is this possible? And if so, why would they do such a thing? > > Yes, this is possible, I've seen this before. > > Reason is that it allows for totally software and hardware agnostic fan > speed control. CPU safety is guaranteed by the fan itself and there is > no way to screw it (short of removing or under-powering the fan itself.) > > Obviously the major drawback is that it takes control away from the > user, so I would stay away from such hardware if I can. But for lambda > users it makes some sense. Eww... In that case, they should the high speed make available to UEFI/software anyway. If the fan thinks the speed the user chose is too low, it can still increase it. But what it does is exactly the opposite: if the user chooses a low speed, the fan speed does not increase, either, even at high temperature. And if they *must* do it this way, the fan should speed up long before 70°C (which is a value I actually reach). But OK, this means there is nothing wrong with any hardware or driver, but it's just an ignorantly designed fan. So thanks a lot or your response, Sören _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
