g760a.rst (1294B)
1Kernel driver g760a 2=================== 3 4Supported chips: 5 6 * Global Mixed-mode Technology Inc. G760A 7 8 Prefix: 'g760a' 9 10 Datasheet: Publicly available at the GMT website 11 12 http://www.gmt.com.tw/product/datasheet/EDS-760A.pdf 13 14Author: Herbert Valerio Riedel <hvr@gnu.org> 15 16Description 17----------- 18 19The GMT G760A Fan Speed PWM Controller is connected directly to a fan 20and performs closed-loop control of the fan speed. 21 22The fan speed is programmed by setting the period via 'pwm1' of two 23consecutive speed pulses. The period is defined in terms of clock 24cycle counts of an assumed 32kHz clock source. 25 26Setting a period of 0 stops the fan; setting the period to 255 sets 27fan to maximum speed. 28 29The measured fan rotation speed returned via 'fan1_input' is derived 30from the measured speed pulse period by assuming again a 32kHz clock 31source and a 2 pulse-per-revolution fan. 32 33The 'alarms' file provides access to the two alarm bits provided by 34the G760A chip's status register: Bit 0 is set when the actual fan 35speed differs more than 20% with respect to the programmed fan speed; 36bit 1 is set when fan speed is below 1920 RPM. 37 38The g760a driver will not update its values more frequently than every 39other second; reading them more often will do no harm, but will return 40'old' values.