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