Root/Documentation/hwmon/pc87427

1Kernel driver pc87427
2=====================
3
4Supported chips:
5  * National Semiconductor PC87427
6    Prefix: 'pc87427'
7    Addresses scanned: none, address read from Super I/O config space
8    Datasheet: No longer available
9
10Author: Jean Delvare <khali@linux-fr.org>
11
12Thanks to Amir Habibi at Candelis for setting up a test system, and to
13Michael Kress for testing several iterations of this driver.
14
15
16Description
17-----------
18
19The National Semiconductor Super I/O chip includes complete hardware
20monitoring capabilities. It can monitor up to 18 voltages, 8 fans and
216 temperature sensors. Only the fans and temperatures are supported at
22the moment, voltages aren't.
23
24This chip also has fan controlling features (up to 4 PWM outputs),
25which are partly supported by this driver.
26
27The driver assumes that no more than one chip is present, which seems
28reasonable.
29
30
31Fan Monitoring
32--------------
33
34Fan rotation speeds are reported as 14-bit values from a gated clock
35signal. Speeds down to 83 RPM can be measured.
36
37An alarm is triggered if the rotation speed drops below a programmable
38limit. Another alarm is triggered if the speed is too low to be measured
39(including stalled or missing fan).
40
41
42Fan Speed Control
43-----------------
44
45Fan speed can be controlled by PWM outputs. There are 4 possible modes:
46always off, always on, manual and automatic. The latter isn't supported
47by the driver: you can only return to that mode if it was the original
48setting, and the configuration interface is missing.
49
50
51Temperature Monitoring
52----------------------
53
54The PC87427 relies on external sensors (following the SensorPath
55standard), so the resolution and range depend on the type of sensor
56connected. The integer part can be 8-bit or 9-bit, and can be signed or
57not. I couldn't find a way to figure out the external sensor data
58temperature format, so user-space adjustment (typically by a factor 2)
59may be required.
60

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