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- 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.
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