g760a.rst 1.3 KB

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