96 lines
3.3 KiB
ReStructuredText
96 lines
3.3 KiB
ReStructuredText
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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* National Semiconductor LM64
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Prefix: 'lm64'
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Addresses scanned: I2C 0x18 and 0x4e
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/pf/LM/LM64.html
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* National Semiconductor LM96163
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Prefix: 'lm96163'
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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/LM96163.html
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Author: Jean Delvare <jdelvare@suse.de>
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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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https://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. Only the original
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LM63 suffers from this limitation, the LM64 and LM96163 have separate pins
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for fan monitoring and alert out. On the LM64, monitoring is always enabled;
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on the LM96163 it can be disabled.
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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 configured with
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the update_interval sysfs attribute; reading them more often will do no harm,
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but will return 'old' values. Values in the automatic fan control lookup table
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(attributes pwm1_auto_*) have their own independent lifetime of 5 seconds.
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The LM64 is effectively an LM63 with GPIO lines. The driver does not
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support these GPIO lines at present.
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The LM96163 is an enhanced version of LM63 with improved temperature accuracy
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and better PWM resolution. For LM96163, the external temperature sensor type is
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configurable as CPU embedded diode(1) or 3904 transistor(2).
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