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1 | Kernel driver lm63 | ||
2 | ================== | ||
3 | |||
4 | Supported chips: | ||
5 | * National Semiconductor LM63 | ||
6 | Prefix: 'lm63' | ||
7 | Addresses scanned: I2C 0x4c | ||
8 | Datasheet: Publicly available at the National Semiconductor website | ||
9 | http://www.national.com/pf/LM/LM63.html | ||
10 | |||
11 | Author: Jean Delvare <khali@linux-fr.org> | ||
12 | |||
13 | Thanks go to Tyan and especially Alex Buckingham for setting up a remote | ||
14 | access to their S4882 test platform for this driver. | ||
15 | http://www.tyan.com/ | ||
16 | |||
17 | Description | ||
18 | ----------- | ||
19 | |||
20 | The LM63 is a digital temperature sensor with integrated fan monitoring | ||
21 | and control. | ||
22 | |||
23 | The LM63 is basically an LM86 with fan speed monitoring and control | ||
24 | capabilities added. It misses some of the LM86 features though: | ||
25 | - No low limit for local temperature. | ||
26 | - No critical limit for local temperature. | ||
27 | - Critical limit for remote temperature can be changed only once. We | ||
28 | will consider that the critical limit is read-only. | ||
29 | |||
30 | The datasheet isn't very clear about what the tachometer reading is. | ||
31 | |||
32 | An explanation from National Semiconductor: The two lower bits of the read | ||
33 | value have to be masked out. The value is still 16 bit in width. | ||
34 | |||
35 | All temperature values are given in degrees Celsius. Resolution is 1.0 | ||
36 | degree for the local temperature, 0.125 degree for the remote temperature. | ||
37 | |||
38 | The fan speed is measured using a tachometer. Contrary to most chips which | ||
39 | store the value in an 8-bit register and have a selectable clock divider | ||
40 | to make sure that the result will fit in the register, the LM63 uses 16-bit | ||
41 | value for measuring the speed of the fan. It can measure fan speeds down to | ||
42 | 83 RPM, at least in theory. | ||
43 | |||
44 | Note that the pin used for fan monitoring is shared with an alert out | ||
45 | function. Depending on how the board designer wanted to use the chip, fan | ||
46 | speed monitoring will or will not be possible. The proper chip configuration | ||
47 | is left to the BIOS, and the driver will blindly trust it. | ||
48 | |||
49 | A PWM output can be used to control the speed of the fan. The LM63 has two | ||
50 | PWM modes: manual and automatic. Automatic mode is not fully implemented yet | ||
51 | (you cannot define your custom PWM/temperature curve), and mode change isn't | ||
52 | supported either. | ||
53 | |||
54 | The lm63 driver will not update its values more frequently than every | ||
55 | second; reading them more often will do no harm, but will return 'old' | ||
56 | values. | ||
57 | |||