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Jean Delvare
08b64e8200
git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@2028 7894878c-1315-0410-8ee3-d5d059ff63e0
126 lines
4.2 KiB
Plaintext
126 lines
4.2 KiB
Plaintext
Sensors chip driver for MAXIM MAX6650 / MAX6651 fan controllers
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===============================================================
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Chip notes
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----------
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The MAX6551 is a fan controller. It has two distinct functions:
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1) Speed control, with feedback, for a single fan. The code can write
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to a register requesting that the fan run at a certain speed, and the
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chip will adjust the fan voltage until it reaches that speed. This
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is called "closed loop" mode in the datasheet.
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2) Speed measurement (tachometers) for up to four fans, including the
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controlled one.
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The MAX6550 is similar but only has one measurement tachometer.
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Both chips have a few general purpose i/o pins, some of which can be
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configured to have special functions. At the time of writing an overview
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of the chip, with links to the datasheet, can be seen at:
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http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2296/ln/en
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If that has moved searching for MAX6550 from Maxim's home page should
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work.
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Driver state
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------------
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Currently the driver provides the following entries in /proc/sys/
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dev/sensors/max6650-xxx/:
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fan1 through fan4 (read only): the current measured fan speeds, in
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rpm.
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speed (read/write): when written, sets the chip to closed loop mode and
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sets the configured speed, in rpm, to the value written. When read returns
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the configured speed, again in rpm.
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xdump (read only): returns all of the chip register values, except the
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tachometers. Used for debug, and should probably go away or be conditionally
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compiled.
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The MAX665x uses byte wide registers with various scaling factors and
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some more or less complex equations (in the datasheet) relating register
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values to real world values. The driver takes care of all of this.
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Note that the measured speed ("fan1") never exactly matches the set speed
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("speed") because of the coarse resolution of the underlying registers.
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Assumptions
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-----------
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The driver assumes that:
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o The MAX665x is running from its internal 254 kHz clock, not an
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external clock.
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o The monitored fans produce two pulses per rotation (This same
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assumption is made by Maxim throughout the datasheet.)
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o The tachometer count time (register 0x16) has been configured suitably
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for the fans in use, perhaps by some boot code. The driver reads this
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register to compute rpm, but never writes to it.
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o The speed controller prescale (low three bits of register 0x04) has
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been configured suitably for the fans in use, perhaps by some boot
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code. The driver reads these bits to compute rpm, but never changes
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them.
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The driver currently never reads or writes any other configuration
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(gpio config, alarms, 5V/12V setting).
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Bugs
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----
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o The driver assumes too much: it should be possible to set more of the
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configuration dynamically instead of assuming that some other code has
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done it.
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o It does not differentiate between a MAX6550 and a MAX6551, as I can
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see no obvious way to do this. It has only been tested with a MAX6551
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so if anyone gets a board with a MAX6550 to test with maybe something
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will be revealed, such as the three missing tachometer registers
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returning all ones or something. (OK, so maybe I should have called
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this driver max6651, and ignored the max6650 totally...)
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o The /proc names don't match the standards in doc/developers/proc,
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as this chip doesn't map well to other fan controllers,
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Detection notes
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---------------
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The module will autodetect the presence of a max6650 or max6651 at any
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of the four possible I2C addresses for these devices. There is no ID
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register, but there are several registers with all zero bits at the
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high end. The driver checks that all of these are in fact zero before
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declaring the chip to be a MAX6550/1.
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sensors-detect
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--------------
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Support for MAX6650/1 has been added to sensors-detect. It has been
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tested as correctly detecting a MAX6551 at I2C address 0x1B. Like the
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driver, it cannot yet distinguish a MAX6650 and MAX6651.
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prog/sensors
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------------
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Initial read-only support has been added to the "sensors" program.
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Testing
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-------
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The driver and associated programs have been tested under Linux 2.4.18
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running on an embedded Intel XScale processor (actually an IXP425 running
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in big-endian mode) with a MAX6651 chip.
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Author
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------
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John Morris (john.morris@spirentcom.com)
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