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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.
+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
+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.