adt7475.rst

  1Kernel driver adt7475
  2=====================
  3
  4Supported chips:
  5
  6  * Analog Devices ADT7473
  7
  8    Prefix: 'adt7473'
  9
 10    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
 11
 12    Datasheet: Publicly available at the On Semiconductors website
 13
 14  * Analog Devices ADT7475
 15
 16    Prefix: 'adt7475'
 17
 18    Addresses scanned: I2C 0x2E
 19
 20    Datasheet: Publicly available at the On Semiconductors website
 21
 22  * Analog Devices ADT7476
 23
 24    Prefix: 'adt7476'
 25
 26    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
 27
 28    Datasheet: Publicly available at the On Semiconductors website
 29
 30  * Analog Devices ADT7490
 31
 32    Prefix: 'adt7490'
 33
 34    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
 35
 36    Datasheet: Publicly available at the On Semiconductors website
 37
 38Authors:
 39	- Jordan Crouse
 40	- Hans de Goede
 41	- Darrick J. Wong (documentation)
 42	- Jean Delvare
 43
 44
 45Description
 46-----------
 47
 48This driver implements support for the Analog Devices ADT7473, ADT7475,
 49ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in
 50minor details. The ADT7476 has additional features, including extra voltage
 51measurement inputs and VID support. The ADT7490 also has additional
 52features, including extra voltage measurement inputs and PECI support. All
 53the supported chips will be collectively designed by the name "ADT747x" in
 54the rest of this document.
 55
 56The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
 57specification. Using an analog to digital converter it measures three (3)
 58temperatures and two (2) or more voltages. It has four (4) 16-bit counters
 59for measuring fan speed. There are three (3) PWM outputs that can be used
 60to control fan speed.
 61
 62A sophisticated control system for the PWM outputs is designed into the
 63ADT747x that allows fan speed to be adjusted automatically based on any of the
 64three temperature sensors. Each PWM output is individually adjustable and
 65programmable. Once configured, the ADT747x will adjust the PWM outputs in
 66response to the measured temperatures without further host intervention.
 67This feature can also be disabled for manual control of the PWM's.
 68
 69Each of the measured inputs (voltage, temperature, fan speed) has
 70corresponding high/low limit values. The ADT747x will signal an ALARM if
 71any measured value exceeds either limit.
 72
 73The ADT747x samples all inputs continuously. The driver will not read
 74the registers more often than once every other second. Further,
 75configuration data is only read once per minute.
 76
 77Chip Differences Summary
 78------------------------
 79
 80ADT7473:
 81  * 2 voltage inputs
 82  * system acoustics optimizations (not implemented)
 83
 84ADT7475:
 85  * 2 voltage inputs
 86
 87ADT7476:
 88  * 5 voltage inputs
 89  * VID support
 90
 91ADT7490:
 92  * 6 voltage inputs
 93  * 1 Imon input
 94  * PECI support (not implemented)
 95  * 2 GPIO pins (not implemented)
 96  * system acoustics optimizations (not implemented)
 97
 98Sysfs Mapping
 99-------------
100
101==== =========== =========== ========= ==========
102in   ADT7490     ADT7476     ADT7475   ADT7473
103==== =========== =========== ========= ==========
104in0  2.5VIN (22) 2.5VIN (22) -         -
105in1  VCCP   (23) VCCP   (23) VCCP (14) VCCP (14)
106in2  VCC    (4)  VCC    (4)  VCC  (4)  VCC  (3)
107in3  5VIN   (20) 5VIN   (20)
108in4  12VIN  (21) 12VIN  (21)
109in5  VTT    (8)
110in6  Imon   (19)
111==== =========== =========== ========= ==========
112
113Special Features
114----------------
115
116The ADT747x has a 10-bit ADC and can therefore measure temperatures
117with a resolution of 0.25 degree Celsius. Temperature readings can be
118configured either for two's complement format or "Offset 64" format,
119wherein 64 is subtracted from the raw value to get the temperature value.
120
121The datasheet is very detailed and describes a procedure for determining
122an optimal configuration for the automatic PWM control.
123
124Fan Speed Control
125-----------------
126
127The driver exposes two trip points per PWM channel.
128
129- point1: Set the PWM speed at the lower temperature bound
130- point2: Set the PWM speed at the higher temperature bound
131
132The ADT747x will scale the PWM linearly between the lower and higher PWM
133speed when the temperature is between the two temperature boundaries.
134Temperature boundaries are associated to temperature channels rather than
135PWM outputs, and a given PWM output can be controlled by several temperature
136channels. As a result, the ADT747x may compute more than one PWM value
137for a channel at a given time, in which case the maximum value (fastest
138fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
139
140Fan speed may be set to maximum when the temperature sensor associated with
141the PWM control exceeds temp#_max.
142
143At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at the
144minimum (i.e. auto_point1_pwm). This behaviour can be configured using the
145`pwm[1-*]_stall_disable sysfs attribute`. A value of 0 means the fans will shut
146off. A value of 1 means the fans will run at auto_point1_pwm.
147
148The responsiveness of the ADT747x to temperature changes can be configured.
149This allows smoothing of the fan speed transition. To set the transition time
150set the value in ms in the `temp[1-*]_smoothing` sysfs attribute.
151
152Notes
153-----
154
155The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
156Unfortunately, they fail to set the i2c adapter class, so this driver may
157fail to find the chip until the nvidia driver is patched.