| 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. |
