Description¶

This driver implements support for the Analog Devices ADT7473, ADT7475,ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only inminor details. The ADT7476 has additional features, including extra voltagemeasurement inputs and VID support. The ADT7490 also has additionalfeatures, including extra voltage measurement inputs and PECI support. Allthe supported chips will be collectively designed by the name “ADT747x” inthe rest of this document.

The ADT747x uses the 2-wire interface compatible with the SMBus 2.0specification. Using an analog to digital converter it measures three (3)temperatures and two (2) or more voltages. It has four (4) 16-bit countersfor measuring fan speed. There are three (3) PWM outputs that can be usedto control fan speed.

A sophisticated control system for the PWM outputs is designed into theADT747x that allows fan speed to be adjusted automatically based on any of thethree temperature sensors. Each PWM output is individually adjustable andprogrammable. Once configured, the ADT747x will adjust the PWM outputs inresponse to the measured temperatures without further host intervention.This feature can also be disabled for manual control of the PWM’s.

Each of the measured inputs (voltage, temperature, fan speed) hascorresponding high/low limit values. The ADT747x will signal an ALARM ifany measured value exceeds either limit.

The ADT747x samples all inputs continuously. The driver will not readthe registers more often than once every other second. Further,configuration data is only read once per minute.

Chip Differences Summary¶

ADT7473:

• 2 voltage inputs
• system acoustics optimizations (not implemented)

ADT7475:

• 2 voltage inputs

ADT7476:

• 5 voltage inputs
• VID support

ADT7490:

• 6 voltage inputs
• 1 Imon input (not implemented)
• PECI support (not implemented)
• 2 GPIO pins (not implemented)
• system acoustics optimizations (not implemented)

Sysfs Mapping¶

Special Features¶

The ADT747x has a 10-bit ADC and can therefore measure temperatureswith a resolution of 0.25 degree Celsius. Temperature readings can beconfigured either for two’s complement format or “Offset 64” format,wherein 64 is subtracted from the raw value to get the temperature value.

The datasheet is very detailed and describes a procedure for determiningan optimal configuration for the automatic PWM control.

Fan Speed Control¶

The driver exposes two trip points per PWM channel.

• point1: Set the PWM speed at the lower temperature bound
• point2: Set the PWM speed at the higher temperature bound

The ADT747x will scale the PWM linearly between the lower and higher PWMspeed when the temperature is between the two temperature boundaries.Temperature boundaries are associated to temperature channels rather thanPWM outputs, and a given PWM output can be controlled by several temperaturechannels. As a result, the ADT747x may compute more than one PWM valuefor a channel at a given time, in which case the maximum value (fastestfan speed) is applied. PWM values range from 0 (off) to 255 (full speed).

Fan speed may be set to maximum when the temperature sensor associated withthe PWM control exceeds temp#_max.

At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at theminimum (i.e. auto_point1_pwm). This behaviour can be configured using thepwm[1-*]_stall_disable sysfs attribute. A value of 0 means the fans will shutoff. A value of 1 means the fans will run at auto_point1_pwm.

The responsiveness of the ADT747x to temperature changes can be configured.This allows smoothing of the fan speed transition. To set the transition timeset the value in ms in thetemp[1-*]_smoothing sysfs attribute.

Notes¶

The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.Unfortunately, they fail to set the i2c adapter class, so this driver mayfail to find the chip until the nvidia driver is patched.