forked from Minki/linux
[PATCH] I2C: add adm9240 driver documentation
This patch adds adm9240 driver doc, with thanks to Rudolf Marek for review. Signed-off-by: Grant Coady <gcoady@gmail.com> Acked-by: Rudolf Marek <r.marek@sh.cvut.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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Grant Coady
Greg Kroah-Hartman
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Documentation/i2c/chips/adm9240
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Documentation/i2c/chips/adm9240
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Kernel driver adm9240
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=====================
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Supported chips:
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* Analog Devices ADM9240
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Prefix: 'adm9240'
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Addresses scanned: I2C 0x2c - 0x2f
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Datasheet: Publicly available at the Analog Devices website
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http://www.analog.com/UploadedFiles/Data_Sheets/79857778ADM9240_0.pdf
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* Dallas Semiconductor DS1780
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Prefix: 'ds1780'
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Addresses scanned: I2C 0x2c - 0x2f
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Datasheet: Publicly available at the Dallas Semiconductor (Maxim) website
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http://pdfserv.maxim-ic.com/en/ds/DS1780.pdf
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* National Semiconductor LM81
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Prefix: 'lm81'
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Addresses scanned: I2C 0x2c - 0x2f
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/ds.cgi/LM/LM81.pdf
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Authors:
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Frodo Looijaard <frodol@dds.nl>,
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Philip Edelbrock <phil@netroedge.com>,
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Michiel Rook <michiel@grendelproject.nl>,
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Grant Coady <gcoady@gmail.com> with guidance
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from Jean Delvare <khali@linux-fr.org>
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Interface
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---------
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The I2C addresses listed above assume BIOS has not changed the
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chip MSB 5-bit address. Each chip reports a unique manufacturer
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identification code as well as the chip revision/stepping level.
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Description
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-----------
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[From ADM9240] The ADM9240 is a complete system hardware monitor for
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microprocessor-based systems, providing measurement and limit comparison
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of up to four power supplies and two processor core voltages, plus
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temperature, two fan speeds and chassis intrusion. Measured values can
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be read out via an I2C-compatible serial System Management Bus, and values
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for limit comparisons can be programmed in over the same serial bus. The
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high speed successive approximation ADC allows frequent sampling of all
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analog channels to ensure a fast interrupt response to any out-of-limit
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measurement.
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The ADM9240, DS1780 and LM81 are register compatible, the following
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details are common to the three chips. Chip differences are described
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after this section.
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Measurements
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------------
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The measurement cycle
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The adm9240 driver will take a measurement reading no faster than once
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each two seconds. User-space may read sysfs interface faster than the
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measurement update rate and will receive cached data from the most
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recent measurement.
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ADM9240 has a very fast 320us temperature and voltage measurement cycle
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with independent fan speed measurement cycles counting alternating rising
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edges of the fan tacho inputs.
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DS1780 measurement cycle is about once per second including fan speed.
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LM81 measurement cycle is about once per 400ms including fan speed.
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The LM81 12-bit extended temperature measurement mode is not supported.
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Temperature
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-----------
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On chip temperature is reported as degrees Celsius as 9-bit signed data
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with resolution of 0.5 degrees Celsius. High and low temperature limits
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are 8-bit signed data with resolution of one degree Celsius.
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Temperature alarm is asserted once the temperature exceeds the high limit,
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and is cleared when the temperature falls below the temp1_max_hyst value.
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Fan Speed
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---------
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Two fan tacho inputs are provided, the ADM9240 gates an internal 22.5kHz
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clock via a divider to an 8-bit counter. Fan speed (rpm) is calculated by:
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rpm = (22500 * 60) / (count * divider)
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Automatic fan clock divider
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* User sets 0 to fan_min limit
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- low speed alarm is disabled
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- fan clock divider not changed
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- auto fan clock adjuster enabled for valid fan speed reading
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* User sets fan_min limit too low
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- low speed alarm is enabled
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- fan clock divider set to max
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- fan_min set to register value 254 which corresponds
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to 664 rpm on adm9240
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- low speed alarm will be asserted if fan speed is
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less than minimum measurable speed
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- auto fan clock adjuster disabled
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* User sets reasonable fan speed
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- low speed alarm is enabled
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- fan clock divider set to suit fan_min
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- auto fan clock adjuster enabled: adjusts fan_min
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* User sets unreasonably high low fan speed limit
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- resolution of the low speed limit may be reduced
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- alarm will be asserted
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- auto fan clock adjuster enabled: adjusts fan_min
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* fan speed may be displayed as zero until the auto fan clock divider
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adjuster brings fan speed clock divider back into chip measurement
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range, this will occur within a few measurement cycles.
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Analog Output
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-------------
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An analog output provides a 0 to 1.25 volt signal intended for an external
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fan speed amplifier circuit. The analog output is set to maximum value on
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power up or reset. This doesn't do much on the test Intel SE440BX-2.
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Voltage Monitor
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Voltage (IN) measurement is internally scaled:
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nr label nominal maximum resolution
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mV mV mV
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0 +2.5V 2500 3320 13.0
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1 Vccp1 2700 3600 14.1
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2 +3.3V 3300 4380 17.2
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3 +5V 5000 6640 26.0
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4 +12V 12000 15940 62.5
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5 Vccp2 2700 3600 14.1
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The reading is an unsigned 8-bit value, nominal voltage measurement is
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represented by a reading of 192, being 3/4 of the measurement range.
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An alarm is asserted for any voltage going below or above the set limits.
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The driver reports and accepts voltage limits scaled to the above table.
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VID Monitor
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-----------
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The chip has five inputs to read the 5-bit VID and reports the mV value
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based on detected CPU type.
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Chassis Intrusion
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-----------------
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An alarm is asserted when the CI pin goes active high. The ADM9240
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Datasheet has an example of an external temperature sensor driving
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this pin. On an Intel SE440BX-2 the Chassis Intrusion header is
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connected to a normally open switch.
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The ADM9240 provides an internal open drain on this line, and may output
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a 20 ms active low pulse to reset an external Chassis Intrusion latch.
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Clear the CI latch by writing value 1 to the sysfs chassis_clear file.
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Alarm flags reported as 16-bit word
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bit label comment
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--- ------------- --------------------------
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0 +2.5 V_Error high or low limit exceeded
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1 VCCP_Error high or low limit exceeded
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2 +3.3 V_Error high or low limit exceeded
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3 +5 V_Error high or low limit exceeded
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4 Temp_Error temperature error
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6 FAN1_Error fan low limit exceeded
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7 FAN2_Error fan low limit exceeded
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8 +12 V_Error high or low limit exceeded
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9 VCCP2_Error high or low limit exceeded
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12 Chassis_Error CI pin went high
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Remaining bits are reserved and thus undefined. It is important to note
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that alarm bits may be cleared on read, user-space may latch alarms and
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provide the end-user with a method to clear alarm memory.
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