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xianfeng |
Kernel driver lm63
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==================
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Supported chips:
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* National Semiconductor LM63
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Prefix: 'lm63'
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Addresses scanned: I2C 0x4c
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/pf/LM/LM63.html
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Author: Jean Delvare
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Thanks go to Tyan and especially Alex Buckingham for setting up a remote
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access to their S4882 test platform for this driver.
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http://www.tyan.com/
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Description
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-----------
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The LM63 is a digital temperature sensor with integrated fan monitoring
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and control.
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The LM63 is basically an LM86 with fan speed monitoring and control
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capabilities added. It misses some of the LM86 features though:
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- No low limit for local temperature.
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- No critical limit for local temperature.
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- Critical limit for remote temperature can be changed only once. We
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will consider that the critical limit is read-only.
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The datasheet isn't very clear about what the tachometer reading is.
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An explanation from National Semiconductor: The two lower bits of the read
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value have to be masked out. The value is still 16 bit in width.
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All temperature values are given in degrees Celsius. Resolution is 1.0
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degree for the local temperature, 0.125 degree for the remote temperature.
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The fan speed is measured using a tachometer. Contrary to most chips which
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store the value in an 8-bit register and have a selectable clock divider
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to make sure that the result will fit in the register, the LM63 uses 16-bit
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value for measuring the speed of the fan. It can measure fan speeds down to
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83 RPM, at least in theory.
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Note that the pin used for fan monitoring is shared with an alert out
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function. Depending on how the board designer wanted to use the chip, fan
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speed monitoring will or will not be possible. The proper chip configuration
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is left to the BIOS, and the driver will blindly trust it.
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A PWM output can be used to control the speed of the fan. The LM63 has two
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PWM modes: manual and automatic. Automatic mode is not fully implemented yet
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(you cannot define your custom PWM/temperature curve), and mode change isn't
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supported either.
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The lm63 driver will not update its values more frequently than every
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second; reading them more often will do no harm, but will return 'old'
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values.
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