Description¶

The GMT G760A Fan Speed PWM Controller is connected directly to a fanand performs closed-loop control of the fan speed.

The fan speed is programmed by setting the period via ‘pwm1’ of twoconsecutive speed pulses. The period is defined in terms of clockcycle counts of an assumed 32kHz clock source.

Setting a period of 0 stops the fan; setting the period to 255 setsfan to maximum speed.

The measured fan rotation speed returned via ‘fan1_input’ is derivedfrom the measured speed pulse period by assuming again a 32kHz clocksource and a 2 pulse-per-revolution fan.

The ‘alarms’ file provides access to the two alarm bits provided bythe G760A chip’s status register: Bit 0 is set when the actual fanspeed differs more than 20% with respect to the programmed fan speed;bit 1 is set when fan speed is below 1920 RPM.

The g760a driver will not update its values more frequently than everyother second; reading them more often will do no harm, but will return‘old’ values.