241937b863
Add a sentence about when fan speed increases to maximum. Signed-off-by: Darrick J. Wong <djwong@us.ibm.com> Acked-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
81 lines
3.0 KiB
Plaintext
81 lines
3.0 KiB
Plaintext
Kernel driver adt7473
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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 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 ADT7473 chip family.
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The LM85 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 three (3) 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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LM85 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 ADT7473 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 ADT7473 will signal an ALARM if
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any measured value exceeds either limit.
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The ADT7473 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 ADT7473 have a 10-bit ADC and can therefore measure temperatures
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with 0.25 degC resolution. Temperature readings can be configured either
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for twos complement format or "Offset 64" format, wherein 63 is subtracted
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from the raw value to get the temperature value.
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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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Hardware Configurations
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-----------------------
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The ADT7473 chips have an optional SMBALERT output that can be used to
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signal the chipset in case a limit is exceeded or the temperature sensors
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fail. Individual sensor interrupts can be masked so they won't trigger
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SMBALERT. The SMBALERT output if configured replaces the PWM2 function.
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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 ADT7473 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 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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