| Herbert Valerio Riedel | 3bcfa9e | 2009-04-06 19:00:30 -0700 | [diff] [blame] | 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. |