Documentation/hwmon/adt7475

   1 Kernel driver adt7475
   2 =====================
   3
   4 Supported chips:
   5   * Analog Devices ADT7473
   6     Prefix: 'adt7473'
   7     Addresses scanned: I2C 0x2C, 0x2D, 0x2E
   8     Datasheet: Publicly available at the On Semiconductors website
   9   * Analog Devices ADT7475
  10     Prefix: 'adt7475'
  11     Addresses scanned: I2C 0x2E
  12     Datasheet: Publicly available at the On Semiconductors website
  13   * Analog Devices ADT7476
  14     Prefix: 'adt7476'
  15     Addresses scanned: I2C 0x2C, 0x2D, 0x2E
  16     Datasheet: Publicly available at the On Semiconductors website
  17   * Analog Devices ADT7490
  18     Prefix: 'adt7490'
  19     Addresses scanned: I2C 0x2C, 0x2D, 0x2E
  20     Datasheet: Publicly available at the On Semiconductors website
  21
  22 Authors:
  23         Jordan Crouse
  24         Hans de Goede
  25         Darrick J. Wong (documentation)
  26         Jean Delvare
  27
  28
  29 Description
  30 -----------
  31
  32 This driver implements support for the Analog Devices ADT7473, ADT7475,
  33 ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in
  34 minor details. The ADT7476 has additional features, including extra voltage
  35 measurement inputs and VID support. The ADT7490 also has additional
  36 features, including extra voltage measurement inputs and PECI support. All
  37 the supported chips will be collectively designed by the name "ADT747x" in
  38 the rest of this document.
  39
  40 The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
  41 specification. Using an analog to digital converter it measures three (3)
  42 temperatures and two (2) or more voltages. It has four (4) 16-bit counters
  43 for measuring fan speed. There are three (3) PWM outputs that can be used
  44 to control fan speed.
  45
  46 A sophisticated control system for the PWM outputs is designed into the
  47 ADT747x that allows fan speed to be adjusted automatically based on any of the
  48 three temperature sensors. Each PWM output is individually adjustable and
  49 programmable. Once configured, the ADT747x will adjust the PWM outputs in
  50 response to the measured temperatures without further host intervention.
  51 This feature can also be disabled for manual control of the PWM's.
  52
  53 Each of the measured inputs (voltage, temperature, fan speed) has
  54 corresponding high/low limit values. The ADT747x will signal an ALARM if
  55 any measured value exceeds either limit.
  56
  57 The ADT747x samples all inputs continuously. The driver will not read
  58 the registers more often than once every other second. Further,
  59 configuration data is only read once per minute.
  60
  61 Chip Differences Summary
  62 ------------------------
  63
  64 ADT7473:
  65   * 2 voltage inputs
  66   * system acoustics optimizations (not implemented)
  67
  68 ADT7475:
  69   * 2 voltage inputs
  70
  71 ADT7476:
  72   * 5 voltage inputs
  73   * VID support
  74
  75 ADT7490:
  76   * 6 voltage inputs
  77   * 1 Imon input (not implemented)
  78   * PECI support (not implemented)
  79   * 2 GPIO pins (not implemented)
  80   * system acoustics optimizations (not implemented)
  81
  82 Special Features
  83 ----------------
  84
  85 The ADT747x has a 10-bit ADC and can therefore measure temperatures
  86 with a resolution of 0.25 degree Celsius. Temperature readings can be
  87 configured either for two's complement format or "Offset 64" format,
  88 wherein 64 is subtracted from the raw value to get the temperature value.
  89
  90 The datasheet is very detailed and describes a procedure for determining
  91 an optimal configuration for the automatic PWM control.
  92
  93 Fan Speed Control
  94 -----------------
  95
  96 The driver exposes two trip points per PWM channel.
  97
  98 point1: Set the PWM speed at the lower temperature bound
  99 point2: Set the PWM speed at the higher temperature bound
 100
 101 The ADT747x will scale the PWM linearly between the lower and higher PWM
 102 speed when the temperature is between the two temperature boundaries.
 103 Temperature boundaries are associated to temperature channels rather than
 104 PWM outputs, and a given PWM output can be controlled by several temperature
 105 channels. As a result, the ADT747x may compute more than one PWM value
 106 for a channel at a given time, in which case the maximum value (fastest
 107 fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
 108
 109 Fan speed may be set to maximum when the temperature sensor associated with
 110 the PWM control exceeds temp#_max.
 111
 112 Notes
 113 -----
 114
 115 The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
 116 Unfortunately, they fail to set the i2c adapter class, so this driver may
 117 fail to find the chip until the nvidia driver is patched.