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- Kernel driver adt7470
- =====================
- Supported chips:
- * Analog Devices ADT7470
- Prefix: 'adt7470'
- Addresses scanned: I2C 0x2C, 0x2E, 0x2F
- Datasheet: Publicly available at the Analog Devices website
- Author: Darrick J. Wong
- Description
- -----------
- This driver implements support for the Analog Devices ADT7470 chip. There may
- be other chips that implement this interface.
- The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
- specification. Using an analog to digital converter it measures up to ten (10)
- external temperatures. It has four (4) 16-bit counters for measuring fan speed.
- There are four (4) PWM outputs that can be used to control fan speed.
- A sophisticated control system for the PWM outputs is designed into the ADT7470
- that allows fan speed to be adjusted automatically based on any of the ten
- temperature sensors. Each PWM output is individually adjustable and
- programmable. Once configured, the ADT7470 will adjust the PWM outputs in
- response to the measured temperatures with further host intervention. This
- feature can also be disabled for manual control of the PWM's.
- Each of the measured inputs (temperature, fan speed) has corresponding high/low
- limit values. The ADT7470 will signal an ALARM if any measured value exceeds
- either limit.
- The ADT7470 samples all inputs continuously. A kernel thread is started up for
- the purpose of periodically querying the temperature sensors, thus allowing the
- automatic fan pwm control to set the fan speed. The driver will not read the
- registers more often than once every 5 seconds. Further, configuration data is
- only read once per minute.
- Special Features
- ----------------
- The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
- degC resolution.
- The Analog Devices datasheet is very detailed and describes a procedure for
- determining an optimal configuration for the automatic PWM control.
- Configuration Notes
- -------------------
- Besides standard interfaces driver adds the following:
- * PWM Control
- * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
- * pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
- point1: Set the pwm speed at a lower temperature bound.
- point2: Set the pwm speed at a higher temperature bound.
- The ADT7470 will scale the pwm between the lower and higher pwm speed when
- the temperature is between the two temperature boundaries. PWM values range
- from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
- temperature sensor associated with the PWM control exceeds
- pwm#_auto_point2_temp.
- The driver also allows control of the PWM frequency:
- * pwm1_freq
- The PWM frequency is rounded to the nearest one of:
- * 11.0 Hz
- * 14.7 Hz
- * 22.1 Hz
- * 29.4 Hz
- * 35.3 Hz
- * 44.1 Hz
- * 58.8 Hz
- * 88.2 Hz
- * 1.4 kHz
- * 22.5 kHz
- Notes
- -----
- The temperature inputs no longer need to be read periodically from userspace in
- order for the automatic pwm algorithm to run. This was the case for earlier
- versions of the driver.
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