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+Kernel driver adm9240
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+=====================
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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+
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+Measurements
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+------------
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+The measurement cycle
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+
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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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+
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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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+
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+DS1780 measurement cycle is about once per second including fan speed.
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+
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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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+
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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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+
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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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+
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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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+
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+rpm = (22500 * 60) / (count * divider)
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+
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+Automatic fan clock divider
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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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+Voltage Monitor
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+
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+Voltage (IN) measurement is internally scaled:
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+
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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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+
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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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+
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+An alarm is asserted for any voltage going below or above the set limits.
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+
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+The driver reports and accepts voltage limits scaled to the above table.
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+
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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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+
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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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+
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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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+
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+Clear the CI latch by writing value 1 to the sysfs chassis_clear file.
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+
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+Alarm flags reported as 16-bit word
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+
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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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+
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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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Grant Coady