2009-12-10 03:36:02 +08:00
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Kernel driver adt7475
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=====================
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Supported chips:
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* Analog Devices ADT7473
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Prefix: 'adt7473'
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Addresses scanned: I2C 0x2C, 0x2D, 0x2E
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Datasheet: Publicly available at the On Semiconductors website
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* Analog Devices ADT7475
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Prefix: 'adt7475'
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Addresses scanned: I2C 0x2E
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Datasheet: Publicly available at the On Semiconductors website
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Authors:
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Jordan Crouse
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Hans de Goede
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Darrick J. Wong (documentation)
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Description
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-----------
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This driver implements support for the Analog Devices ADT7473 and ADT7475
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chip family. Both chips differ only in minor details. They will be
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collectively designed by the name "ADT747x" in the rest of this document.
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The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
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specification. Using an analog to digital converter it measures three (3)
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temperatures and two (2) voltages. It has four (4) 16-bit counters for
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measuring fan speed. There are three (3) PWM outputs that can be used
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to control fan speed.
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A sophisticated control system for the PWM outputs is designed into the
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ADT747x that allows fan speed to be adjusted automatically based on any of the
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three temperature sensors. Each PWM output is individually adjustable and
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programmable. Once configured, the ADT747x will adjust the PWM outputs in
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response to the measured temperatures without further host intervention.
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This feature can also be disabled for manual control of the PWM's.
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Each of the measured inputs (voltage, temperature, fan speed) has
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corresponding high/low limit values. The ADT747x will signal an ALARM if
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any measured value exceeds either limit.
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The ADT747x samples all inputs continuously. The driver will not read
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the registers more often than once every other second. Further,
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configuration data is only read once per minute.
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Special Features
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----------------
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The ADT747x has a 10-bit ADC and can therefore measure temperatures
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with a resolution of 0.25 degree Celsius. Temperature readings can be
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configured either for two's complement format or "Offset 64" format,
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wherein 64 is subtracted from the raw value to get the temperature value.
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The datasheet is very detailed and describes a procedure for determining
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an optimal configuration for the automatic PWM control.
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Fan Speed Control
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-----------------
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The driver exposes two trip points per PWM channel.
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point1: Set the PWM speed at the lower temperature bound
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point2: Set the PWM speed at the higher temperature bound
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The ADT747x will scale the PWM linearly between the lower and higher PWM
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speed when the temperature is between the two temperature boundaries.
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Temperature boundaries are associated to temperature channels rather than
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PWM outputs, and a given PWM output can be controlled by several temperature
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channels. As a result, the ADT747x may compute more than one PWM value
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for a channel at a given time, in which case the maximum value (fastest
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fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
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Fan speed may be set to maximum when the temperature sensor associated with
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the PWM control exceeds temp#_max.
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Notes
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-----
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The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
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Unfortunately, they fail to set the i2c adapter class, so this driver may
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fail to find the chip until the nvidia driver is patched.
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