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Kernel driver pc87427
=====================
Supported chips:
* National Semiconductor PC87427
Prefix: 'pc87427'
Addresses scanned: none, address read from Super I/O config space
Datasheet: No longer available
Author: Jean Delvare <khali@linux-fr.org>
Thanks to Amir Habibi at Candelis for setting up a test system, and to
Michael Kress for testing several iterations of this driver.
Description
-----------
The National Semiconductor Super I/O chip includes complete hardware
monitoring capabilities. It can monitor up to 18 voltages, 8 fans and
6 temperature sensors. Only the fans and temperatures are supported at
the moment, voltages aren't.
This chip also has fan controlling features (up to 4 PWM outputs),
which are partly supported by this driver.
The driver assumes that no more than one chip is present, which seems
reasonable.
Fan Monitoring
--------------
Fan rotation speeds are reported as 14-bit values from a gated clock
signal. Speeds down to 83 RPM can be measured.
An alarm is triggered if the rotation speed drops below a programmable
limit. Another alarm is triggered if the speed is too low to be measured
(including stalled or missing fan).
Fan Speed Control
-----------------
Fan speed can be controlled by PWM outputs. There are 4 possible modes:
always off, always on, manual and automatic. The latter isn't supported
by the driver: you can only return to that mode if it was the original
setting, and the configuration interface is missing.
Temperature Monitoring
----------------------
The PC87427 relies on external sensors (following the SensorPath
standard), so the resolution and range depend on the type of sensor
connected. The integer part can be 8-bit or 9-bit, and can be signed or
not. I couldn't find a way to figure out the external sensor data
temperature format, so user-space adjustment (typically by a factor 2)
may be required.
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