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1 | Kernel driver adt7473 |
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 Analog Devices website | |
9 | ||
10 | Author: Darrick J. Wong | |
11 | ||
12 | Description | |
13 | ----------- | |
14 | ||
15 | This driver implements support for the Analog Devices ADT7473 chip family. | |
16 | ||
17 | The LM85 uses the 2-wire interface compatible with the SMBUS 2.0 | |
18 | specification. Using an analog to digital converter it measures three (3) | |
19 | temperatures and two (2) voltages. It has three (3) 16-bit counters for | |
20 | measuring fan speed. There are three (3) PWM outputs that can be used | |
21 | to control fan speed. | |
22 | ||
23 | A sophisticated control system for the PWM outputs is designed into the | |
24 | LM85 that allows fan speed to be adjusted automatically based on any of the | |
25 | three temperature sensors. Each PWM output is individually adjustable and | |
26 | programmable. Once configured, the ADT7473 will adjust the PWM outputs in | |
27 | response to the measured temperatures without further host intervention. | |
28 | This feature can also be disabled for manual control of the PWM's. | |
29 | ||
30 | Each of the measured inputs (voltage, temperature, fan speed) has | |
31 | corresponding high/low limit values. The ADT7473 will signal an ALARM if | |
32 | any measured value exceeds either limit. | |
33 | ||
34 | The ADT7473 samples all inputs continuously. The driver will not read | |
35 | the registers more often than once every other second. Further, | |
36 | configuration data is only read once per minute. | |
37 | ||
38 | Special Features | |
39 | ---------------- | |
40 | ||
41 | The ADT7473 have a 10-bit ADC and can therefore measure temperatures | |
42 | with 0.25 degC resolution. Temperature readings can be configured either | |
43 | for twos complement format or "Offset 64" format, wherein 63 is subtracted | |
44 | from the raw value to get the temperature value. | |
45 | ||
46 | The Analog Devices datasheet is very detailed and describes a procedure for | |
47 | determining an optimal configuration for the automatic PWM control. | |
48 | ||
49 | Hardware Configurations | |
50 | ----------------------- | |
51 | ||
52 | The ADT7473 chips have an optional SMBALERT output that can be used to | |
53 | signal the chipset in case a limit is exceeded or the temperature sensors | |
54 | fail. Individual sensor interrupts can be masked so they won't trigger | |
55 | SMBALERT. The SMBALERT output if configured replaces the PWM2 function. | |
56 | ||
57 | Configuration Notes | |
58 | ------------------- | |
59 | ||
60 | Besides standard interfaces driver adds the following: | |
61 | ||
62 | * PWM Control | |
63 | ||
64 | * pwm#_auto_point1_pwm and pwm#_auto_point1_temp and | |
65 | * pwm#_auto_point2_pwm and pwm#_auto_point2_temp - | |
66 | ||
67 | point1: Set the pwm speed at a lower temperature bound. | |
68 | point2: Set the pwm speed at a higher temperature bound. | |
69 | ||
70 | The ADT7473 will scale the pwm between the lower and higher pwm speed when | |
71 | the temperature is between the two temperature boundaries. PWM values range | |
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72 | from 0 (off) to 255 (full speed). Fan speed will be set to maximum when the |
73 | temperature sensor associated with the PWM control exceeds temp#_max. | |
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74 | |
75 | Notes | |
76 | ----- | |
77 | ||
78 | The NVIDIA binary driver presents an ADT7473 chip via an on-card i2c bus. | |
79 | Unfortunately, they fail to set the i2c adapter class, so this driver may | |
80 | fail to find the chip until the nvidia driver is patched. |