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authorDarrick J. Wong <djwong@us.ibm.com>2008-10-17 11:51:20 -0400
committerJean Delvare <khali@mahadeva.delvare>2008-10-17 11:51:20 -0400
commitd664a4809e73c878a43607d584b2e2b60fd07468 (patch)
treec521da804f4fc539ce13146ebfaa9dd546ed03a0 /Documentation/hwmon
parent21d93c14b32f1d74ebed09caca7d6c10cf3f952e (diff)
hwmon: (adt7470) Add documentation
Add at least the bare minimum of documentation for this chip. Signed-off-by: Darrick J. Wong <djwong@us.ibm.com> Signed-off-by: Jean Delvare <khali@linux-fr.org>
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1Kernel driver adt7470
2=====================
3
4Supported chips:
5 * Analog Devices ADT7470
6 Prefix: 'adt7470'
7 Addresses scanned: I2C 0x2C, 0x2E, 0x2F
8 Datasheet: Publicly available at the Analog Devices website
9
10Author: Darrick J. Wong
11
12Description
13-----------
14
15This driver implements support for the Analog Devices ADT7470 chip. There may
16be other chips that implement this interface.
17
18The ADT7470 uses the 2-wire interface compatible with the SMBus 2.0
19specification. Using an analog to digital converter it measures up to ten (10)
20external temperatures. It has four (4) 16-bit counters for measuring fan speed.
21There are four (4) PWM outputs that can be used to control fan speed.
22
23A sophisticated control system for the PWM outputs is designed into the ADT7470
24that allows fan speed to be adjusted automatically based on any of the ten
25temperature sensors. Each PWM output is individually adjustable and
26programmable. Once configured, the ADT7470 will adjust the PWM outputs in
27response to the measured temperatures with further host intervention. This
28feature can also be disabled for manual control of the PWM's.
29
30Each of the measured inputs (temperature, fan speed) has corresponding high/low
31limit values. The ADT7470 will signal an ALARM if any measured value exceeds
32either limit.
33
34The ADT7470 DOES NOT sample all inputs continuously. A single pin on the
35ADT7470 is connected to a multitude of thermal diodes, but the chip must be
36instructed explicitly to read the multitude of diodes. If you want to use
37automatic fan control mode, you must manually read any of the temperature
38sensors or the fan control algorithm will not run. The chip WILL NOT DO THIS
39AUTOMATICALLY; this must be done from userspace. This may be a bug in the chip
40design, given that many other AD chips take care of this. The driver will not
41read the registers more often than once every 5 seconds. Further,
42configuration data is only read once per minute.
43
44Special Features
45----------------
46
47The ADT7470 has a 8-bit ADC and is capable of measuring temperatures with 1
48degC resolution.
49
50The Analog Devices datasheet is very detailed and describes a procedure for
51determining an optimal configuration for the automatic PWM control.
52
53Configuration Notes
54-------------------
55
56Besides standard interfaces driver adds the following:
57
58* PWM Control
59
60* pwm#_auto_point1_pwm and pwm#_auto_point1_temp and
61* pwm#_auto_point2_pwm and pwm#_auto_point2_temp -
62
63point1: Set the pwm speed at a lower temperature bound.
64point2: Set the pwm speed at a higher temperature bound.
65
66The ADT7470 will scale the pwm between the lower and higher pwm speed when
67the temperature is between the two temperature boundaries. PWM values range
68from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the
69temperature sensor associated with the PWM control exceeds
70pwm#_auto_point2_temp.
71
72Notes
73-----
74
75As stated above, the temperature inputs must be read periodically from
76userspace in order for the automatic pwm algorithm to run.