linux/Documentation/hwmon/adt7475
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   1Kernel driver adt7475
   2=====================
   3
   4Supported 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
  22Authors:
  23        Jordan Crouse
  24        Hans de Goede
  25        Darrick J. Wong (documentation)
  26        Jean Delvare
  27
  28
  29Description
  30-----------
  31
  32This driver implements support for the Analog Devices ADT7473, ADT7475,
  33ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in
  34minor details. The ADT7476 has additional features, including extra voltage
  35measurement inputs and VID support. The ADT7490 also has additional
  36features, including extra voltage measurement inputs and PECI support. All
  37the supported chips will be collectively designed by the name "ADT747x" in
  38the rest of this document.
  39
  40The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
  41specification. Using an analog to digital converter it measures three (3)
  42temperatures and two (2) or more voltages. It has four (4) 16-bit counters
  43for measuring fan speed. There are three (3) PWM outputs that can be used
  44to control fan speed.
  45
  46A sophisticated control system for the PWM outputs is designed into the
  47ADT747x that allows fan speed to be adjusted automatically based on any of the
  48three temperature sensors. Each PWM output is individually adjustable and
  49programmable. Once configured, the ADT747x will adjust the PWM outputs in
  50response to the measured temperatures without further host intervention.
  51This feature can also be disabled for manual control of the PWM's.
  52
  53Each of the measured inputs (voltage, temperature, fan speed) has
  54corresponding high/low limit values. The ADT747x will signal an ALARM if
  55any measured value exceeds either limit.
  56
  57The ADT747x samples all inputs continuously. The driver will not read
  58the registers more often than once every other second. Further,
  59configuration data is only read once per minute.
  60
  61Chip Differences Summary
  62------------------------
  63
  64ADT7473:
  65  * 2 voltage inputs
  66  * system acoustics optimizations (not implemented)
  67
  68ADT7475:
  69  * 2 voltage inputs
  70
  71ADT7476:
  72  * 5 voltage inputs
  73  * VID support
  74
  75ADT7490:
  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
  82Special Features
  83----------------
  84
  85The ADT747x has a 10-bit ADC and can therefore measure temperatures
  86with a resolution of 0.25 degree Celsius. Temperature readings can be
  87configured either for two's complement format or "Offset 64" format,
  88wherein 64 is subtracted from the raw value to get the temperature value.
  89
  90The datasheet is very detailed and describes a procedure for determining
  91an optimal configuration for the automatic PWM control.
  92
  93Fan Speed Control
  94-----------------
  95
  96The driver exposes two trip points per PWM channel.
  97
  98point1: Set the PWM speed at the lower temperature bound
  99point2: Set the PWM speed at the higher temperature bound
 100
 101The ADT747x will scale the PWM linearly between the lower and higher PWM
 102speed when the temperature is between the two temperature boundaries.
 103Temperature boundaries are associated to temperature channels rather than
 104PWM outputs, and a given PWM output can be controlled by several temperature
 105channels. As a result, the ADT747x may compute more than one PWM value
 106for a channel at a given time, in which case the maximum value (fastest
 107fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
 108
 109Fan speed may be set to maximum when the temperature sensor associated with
 110the PWM control exceeds temp#_max.
 111
 112Notes
 113-----
 114
 115The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
 116Unfortunately, they fail to set the i2c adapter class, so this driver may
 117fail to find the chip until the nvidia driver is patched.
 118
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