Kernel driver adt7473
======================

Supported chips:
  * Analog Devices ADT7473
    Prefix: 'adt7473'
    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
    Datasheet: Publicly available at the Analog Devices website

Author: Darrick J. Wong

Description
-----------

This driver implements support for the Analog Devices ADT7473 chip family.

The ADT7473 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) 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
ADT7473 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 ADT7473 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 ADT7473 will signal an ALARM if
any measured value exceeds either limit.

The ADT7473 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.

Special Features
----------------

The ADT7473 have a 10-bit ADC and can therefore measure temperatures
with 0.25 degC resolution. Temperature readings can be configured either
for twos complement format or "Offset 64" format, wherein 63 is subtracted
from the raw value to get the temperature value.

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 temp#_auto_point1_temp and
* pwm#_auto_point2_pwm and temp#_auto_point2_temp -

point1: Set the pwm speed at a lower temperature bound.
point2: Set the pwm speed at a higher temperature bound.

The ADT7473 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 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.
