adt7470.rst 2.9 KB

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  1. Kernel driver adt7470
  2. =====================
  3. Supported chips:
  4. * Analog Devices ADT7470
  5. Prefix: 'adt7470'
  6. Addresses scanned: I2C 0x2C, 0x2E, 0x2F
  7. Datasheet: Publicly available at the Analog Devices website
  8. Author: Darrick J. Wong
  9. Description
  10. -----------
  11. This driver implements support for the Analog Devices ADT7470 chip. There may
  12. be other chips that implement this interface.
  13. The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
  14. specification. Using an analog to digital converter it measures up to ten (10)
  15. external temperatures. It has four (4) 16-bit counters for measuring fan speed.
  16. There are four (4) PWM outputs that can be used to control fan speed.
  17. A sophisticated control system for the PWM outputs is designed into the ADT7470
  18. that allows fan speed to be adjusted automatically based on any of the ten
  19. temperature sensors. Each PWM output is individually adjustable and
  20. programmable. Once configured, the ADT7470 will adjust the PWM outputs in
  21. response to the measured temperatures with further host intervention. This
  22. feature can also be disabled for manual control of the PWM's.
  23. Each of the measured inputs (temperature, fan speed) has corresponding high/low
  24. limit values. The ADT7470 will signal an ALARM if any measured value exceeds
  25. either limit.
  26. The ADT7470 samples all inputs continuously. A kernel thread is started up for
  27. the purpose of periodically querying the temperature sensors, thus allowing the
  28. automatic fan pwm control to set the fan speed. The driver will not read the
  29. registers more often than once every 5 seconds. Further, configuration data is
  30. only read once per minute.
  31. Special Features
  32. ----------------
  33. The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
  34. degC resolution.
  35. The Analog Devices datasheet is very detailed and describes a procedure for
  36. determining an optimal configuration for the automatic PWM control.
  37. Configuration Notes
  38. -------------------
  39. Besides standard interfaces driver adds the following:
  40. * PWM Control
  41. * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
  42. * pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
  43. - point1: Set the pwm speed at a lower temperature bound.
  44. - point2: Set the pwm speed at a higher temperature bound.
  45. The ADT7470 will scale the pwm between the lower and higher pwm speed when
  46. the temperature is between the two temperature boundaries. PWM values range
  47. from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
  48. temperature sensor associated with the PWM control exceeds
  49. pwm#_auto_point2_temp.
  50. The driver also allows control of the PWM frequency:
  51. * pwm1_freq
  52. The PWM frequency is rounded to the nearest one of:
  53. * 11.0 Hz
  54. * 14.7 Hz
  55. * 22.1 Hz
  56. * 29.4 Hz
  57. * 35.3 Hz
  58. * 44.1 Hz
  59. * 58.8 Hz
  60. * 88.2 Hz
  61. * 1.4 kHz
  62. * 22.5 kHz
  63. Notes
  64. -----
  65. The temperature inputs no longer need to be read periodically from userspace in
  66. order for the automatic pwm algorithm to run. This was the case for earlier
  67. versions of the driver.