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Kernel driver adt7470
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=====================
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Supported chips:
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* Analog Devices ADT7470
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Prefix: 'adt7470'
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Addresses scanned: I2C 0x2C, 0x2E, 0x2F
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Datasheet: Publicly available at the Analog Devices website
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Author: Darrick J. Wong
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Description
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-----------
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This driver implements support for the Analog Devices ADT7470 chip. There may
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be other chips that implement this interface.
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The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
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specification. Using an analog to digital converter it measures up to ten (10)
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external temperatures. It has four (4) 16-bit counters for measuring fan speed.
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There are four (4) PWM outputs that can be used to control fan speed.
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A sophisticated control system for the PWM outputs is designed into the ADT7470
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that allows fan speed to be adjusted automatically based on any of the ten
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temperature sensors. Each PWM output is individually adjustable and
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programmable. Once configured, the ADT7470 will adjust the PWM outputs in
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response to the measured temperatures with further host intervention. This
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feature can also be disabled for manual control of the PWM's.
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Each of the measured inputs (temperature, fan speed) has corresponding high/low
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limit values. The ADT7470 will signal an ALARM if any measured value exceeds
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either limit.
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The ADT7470 samples all inputs continuously. A kernel thread is started up for
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the purpose of periodically querying the temperature sensors, thus allowing the
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automatic fan pwm control to set the fan speed. The driver will not read the
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registers more often than once every 5 seconds. Further, configuration data is
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only read once per minute.
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Special Features
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----------------
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The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
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degC resolution.
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The Analog Devices datasheet is very detailed and describes a procedure for
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determining an optimal configuration for the automatic PWM control.
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Configuration Notes
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-------------------
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Besides standard interfaces driver adds the following:
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* PWM Control
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* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
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* pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
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point1: Set the pwm speed at a lower temperature bound.
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point2: Set the pwm speed at a higher temperature bound.
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The ADT7470 will scale the pwm between the lower and higher pwm speed when
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the temperature is between the two temperature boundaries. PWM values range
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from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
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temperature sensor associated with the PWM control exceeds
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pwm#_auto_point2_temp.
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Notes
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-----
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The temperature inputs no longer need to be read periodically from userspace in
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order for the automatic pwm algorithm to run. This was the case for earlier
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versions of the driver.
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