| Kernel driver adt7475 | |
| ===================== | |
| Supported chips: | |
| * Analog Devices ADT7473 | |
| Prefix: 'adt7473' | |
| Addresses scanned: I2C 0x2C, 0x2D, 0x2E | |
| Datasheet: Publicly available at the On Semiconductors website | |
| * Analog Devices ADT7475 | |
| Prefix: 'adt7475' | |
| Addresses scanned: I2C 0x2E | |
| Datasheet: Publicly available at the On Semiconductors website | |
| * Analog Devices ADT7476 | |
| Prefix: 'adt7476' | |
| Addresses scanned: I2C 0x2C, 0x2D, 0x2E | |
| Datasheet: Publicly available at the On Semiconductors website | |
| * Analog Devices ADT7490 | |
| Prefix: 'adt7490' | |
| Addresses scanned: I2C 0x2C, 0x2D, 0x2E | |
| Datasheet: Publicly available at the On Semiconductors website | |
| Authors: | |
| Jordan Crouse | |
| Hans de Goede | |
| Darrick J. Wong (documentation) | |
| Jean Delvare | |
| Description | |
| ----------- | |
| This driver implements support for the Analog Devices ADT7473, ADT7475, | |
| ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in | |
| minor details. The ADT7476 has additional features, including extra voltage | |
| measurement inputs and VID support. The ADT7490 also has additional | |
| features, including extra voltage measurement inputs and PECI support. All | |
| the supported chips will be collectively designed by the name "ADT747x" in | |
| the rest of this document. | |
| The ADT747x uses the 2-wire interface compatible with the SMBus 2.0 | |
| specification. Using an analog to digital converter it measures three (3) | |
| temperatures and two (2) or more voltages. It has four (4) 16-bit counters | |
| for measuring fan speed. There are three (3) PWM outputs that can be used | |
| to control fan speed. | |
| A sophisticated control system for the PWM outputs is designed into the | |
| ADT747x that allows fan speed to be adjusted automatically based on any of the | |
| three temperature sensors. Each PWM output is individually adjustable and | |
| programmable. Once configured, the ADT747x will adjust the PWM outputs in | |
| response 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) has | |
| corresponding high/low limit values. The ADT747x will signal an ALARM if | |
| any measured value exceeds either limit. | |
| The ADT747x samples all inputs continuously. The driver will not read | |
| the 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) | |
| Special Features | |
| ---------------- | |
| The ADT747x has a 10-bit ADC and can therefore measure temperatures | |
| with a resolution of 0.25 degree Celsius. Temperature readings can be | |
| configured 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 determining | |
| an 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 PWM | |
| speed when the temperature is between the two temperature boundaries. | |
| Temperature boundaries are associated to temperature channels rather than | |
| PWM outputs, and a given PWM output can be controlled by several temperature | |
| channels. As a result, the ADT747x may compute more than one PWM value | |
| for a channel at a given time, in which case the maximum value (fastest | |
| fan 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 with | |
| the PWM control exceeds temp#_max. | |
| 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 may | |
| fail to find the chip until the nvidia driver is patched. |