Commit | Line | Data |
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f890c6a3 JD |
1 | Kernel driver adt7475 |
2 | ===================== | |
3 | ||
4 | Supported chips: | |
5 | * Analog Devices ADT7473 | |
6 | Prefix: 'adt7473' | |
7 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E | |
8 | Datasheet: Publicly available at the On Semiconductors website | |
9 | * Analog Devices ADT7475 | |
10 | Prefix: 'adt7475' | |
11 | Addresses scanned: I2C 0x2E | |
12 | Datasheet: Publicly available at the On Semiconductors website | |
13 | ||
14 | Authors: | |
15 | Jordan Crouse | |
16 | Hans de Goede | |
17 | Darrick J. Wong (documentation) | |
18 | ||
19 | ||
20 | Description | |
21 | ----------- | |
22 | ||
23 | This driver implements support for the Analog Devices ADT7473 and ADT7475 | |
24 | chip family. Both chips differ only in minor details. They will be | |
25 | collectively designed by the name "ADT747x" in the rest of this document. | |
26 | ||
27 | The ADT747x uses the 2-wire interface compatible with the SMBus 2.0 | |
28 | specification. Using an analog to digital converter it measures three (3) | |
29 | temperatures and two (2) voltages. It has four (4) 16-bit counters for | |
30 | measuring fan speed. There are three (3) PWM outputs that can be used | |
31 | to control fan speed. | |
32 | ||
33 | A sophisticated control system for the PWM outputs is designed into the | |
34 | ADT747x that allows fan speed to be adjusted automatically based on any of the | |
35 | three temperature sensors. Each PWM output is individually adjustable and | |
36 | programmable. Once configured, the ADT747x will adjust the PWM outputs in | |
37 | response to the measured temperatures without further host intervention. | |
38 | This feature can also be disabled for manual control of the PWM's. | |
39 | ||
40 | Each of the measured inputs (voltage, temperature, fan speed) has | |
41 | corresponding high/low limit values. The ADT747x will signal an ALARM if | |
42 | any measured value exceeds either limit. | |
43 | ||
44 | The ADT747x samples all inputs continuously. The driver will not read | |
45 | the registers more often than once every other second. Further, | |
46 | configuration data is only read once per minute. | |
47 | ||
48 | Special Features | |
49 | ---------------- | |
50 | ||
51 | The ADT747x has a 10-bit ADC and can therefore measure temperatures | |
52 | with a resolution of 0.25 degree Celsius. Temperature readings can be | |
53 | configured either for two's complement format or "Offset 64" format, | |
54 | wherein 64 is subtracted from the raw value to get the temperature value. | |
55 | ||
56 | The datasheet is very detailed and describes a procedure for determining | |
57 | an optimal configuration for the automatic PWM control. | |
58 | ||
59 | Fan Speed Control | |
60 | ----------------- | |
61 | ||
62 | The driver exposes two trip points per PWM channel. | |
63 | ||
64 | point1: Set the PWM speed at the lower temperature bound | |
65 | point2: Set the PWM speed at the higher temperature bound | |
66 | ||
67 | The ADT747x will scale the PWM linearly between the lower and higher PWM | |
68 | speed when the temperature is between the two temperature boundaries. | |
69 | Temperature boundaries are associated to temperature channels rather than | |
70 | PWM outputs, and a given PWM output can be controlled by several temperature | |
71 | channels. As a result, the ADT747x may compute more than one PWM value | |
72 | for a channel at a given time, in which case the maximum value (fastest | |
73 | fan speed) is applied. PWM values range from 0 (off) to 255 (full speed). | |
74 | ||
75 | Fan speed may be set to maximum when the temperature sensor associated with | |
76 | the PWM control exceeds temp#_max. | |
77 | ||
78 | Notes | |
79 | ----- | |
80 | ||
81 | The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus. | |
82 | Unfortunately, they fail to set the i2c adapter class, so this driver may | |
83 | fail to find the chip until the nvidia driver is patched. |