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authorGrant Coady <grant_lkml@dodo.com.au>2005-06-03 10:05:19 +1000
committerGreg Kroah-Hartman <gregkh@suse.de>2005-06-21 21:52:03 -0700
commita0ef14837a2298a4748e2a3e8e206f086dd3b21a (patch)
tree78e06fec1c9f157b4c51ca3f4c1f3d142a0a45ca /Documentation/i2c
parenteb071cbbc38efa4b1d707f540de2ec6283ab0894 (diff)
downloadlinux-linaro-stable-a0ef14837a2298a4748e2a3e8e206f086dd3b21a.tar.gz
[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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+Kernel driver adm9240
+=====================
+
+Supported chips:
+ * Analog Devices ADM9240
+ Prefix: 'adm9240'
+ Addresses scanned: I2C 0x2c - 0x2f
+ Datasheet: Publicly available at the Analog Devices website
+ http://www.analog.com/UploadedFiles/Data_Sheets/79857778ADM9240_0.pdf
+
+ * Dallas Semiconductor DS1780
+ Prefix: 'ds1780'
+ Addresses scanned: I2C 0x2c - 0x2f
+ Datasheet: Publicly available at the Dallas Semiconductor (Maxim) website
+ http://pdfserv.maxim-ic.com/en/ds/DS1780.pdf
+
+ * National Semiconductor LM81
+ Prefix: 'lm81'
+ Addresses scanned: I2C 0x2c - 0x2f
+ Datasheet: Publicly available at the National Semiconductor website
+ http://www.national.com/ds.cgi/LM/LM81.pdf
+
+Authors:
+ Frodo Looijaard <frodol@dds.nl>,
+ Philip Edelbrock <phil@netroedge.com>,
+ Michiel Rook <michiel@grendelproject.nl>,
+ Grant Coady <gcoady@gmail.com> with guidance
+ from Jean Delvare <khali@linux-fr.org>
+
+Interface
+---------
+The I2C addresses listed above assume BIOS has not changed the
+chip MSB 5-bit address. Each chip reports a unique manufacturer
+identification code as well as the chip revision/stepping level.
+
+Description
+-----------
+[From ADM9240] The ADM9240 is a complete system hardware monitor for
+microprocessor-based systems, providing measurement and limit comparison
+of up to four power supplies and two processor core voltages, plus
+temperature, two fan speeds and chassis intrusion. Measured values can
+be read out via an I2C-compatible serial System Management Bus, and values
+for limit comparisons can be programmed in over the same serial bus. The
+high speed successive approximation ADC allows frequent sampling of all
+analog channels to ensure a fast interrupt response to any out-of-limit
+measurement.
+
+The ADM9240, DS1780 and LM81 are register compatible, the following
+details are common to the three chips. Chip differences are described
+after this section.
+
+
+Measurements
+------------
+The measurement cycle
+
+The adm9240 driver will take a measurement reading no faster than once
+each two seconds. User-space may read sysfs interface faster than the
+measurement update rate and will receive cached data from the most
+recent measurement.
+
+ADM9240 has a very fast 320us temperature and voltage measurement cycle
+with independent fan speed measurement cycles counting alternating rising
+edges of the fan tacho inputs.
+
+DS1780 measurement cycle is about once per second including fan speed.
+
+LM81 measurement cycle is about once per 400ms including fan speed.
+The LM81 12-bit extended temperature measurement mode is not supported.
+
+Temperature
+-----------
+On chip temperature is reported as degrees Celsius as 9-bit signed data
+with resolution of 0.5 degrees Celsius. High and low temperature limits
+are 8-bit signed data with resolution of one degree Celsius.
+
+Temperature alarm is asserted once the temperature exceeds the high limit,
+and is cleared when the temperature falls below the temp1_max_hyst value.
+
+Fan Speed
+---------
+Two fan tacho inputs are provided, the ADM9240 gates an internal 22.5kHz
+clock via a divider to an 8-bit counter. Fan speed (rpm) is calculated by:
+
+rpm = (22500 * 60) / (count * divider)
+
+Automatic fan clock divider
+
+ * User sets 0 to fan_min limit
+ - low speed alarm is disabled
+ - fan clock divider not changed
+ - auto fan clock adjuster enabled for valid fan speed reading
+
+ * User sets fan_min limit too low
+ - low speed alarm is enabled
+ - fan clock divider set to max
+ - fan_min set to register value 254 which corresponds
+ to 664 rpm on adm9240
+ - low speed alarm will be asserted if fan speed is
+ less than minimum measurable speed
+ - auto fan clock adjuster disabled
+
+ * User sets reasonable fan speed
+ - low speed alarm is enabled
+ - fan clock divider set to suit fan_min
+ - auto fan clock adjuster enabled: adjusts fan_min
+
+ * User sets unreasonably high low fan speed limit
+ - resolution of the low speed limit may be reduced
+ - alarm will be asserted
+ - auto fan clock adjuster enabled: adjusts fan_min
+
+ * fan speed may be displayed as zero until the auto fan clock divider
+ adjuster brings fan speed clock divider back into chip measurement
+ range, this will occur within a few measurement cycles.
+
+Analog Output
+-------------
+An analog output provides a 0 to 1.25 volt signal intended for an external
+fan speed amplifier circuit. The analog output is set to maximum value on
+power up or reset. This doesn't do much on the test Intel SE440BX-2.
+
+Voltage Monitor
+
+Voltage (IN) measurement is internally scaled:
+
+ nr label nominal maximum resolution
+ mV mV mV
+ 0 +2.5V 2500 3320 13.0
+ 1 Vccp1 2700 3600 14.1
+ 2 +3.3V 3300 4380 17.2
+ 3 +5V 5000 6640 26.0
+ 4 +12V 12000 15940 62.5
+ 5 Vccp2 2700 3600 14.1
+
+The reading is an unsigned 8-bit value, nominal voltage measurement is
+represented by a reading of 192, being 3/4 of the measurement range.
+
+An alarm is asserted for any voltage going below or above the set limits.
+
+The driver reports and accepts voltage limits scaled to the above table.
+
+VID Monitor
+-----------
+The chip has five inputs to read the 5-bit VID and reports the mV value
+based on detected CPU type.
+
+Chassis Intrusion
+-----------------
+An alarm is asserted when the CI pin goes active high. The ADM9240
+Datasheet has an example of an external temperature sensor driving
+this pin. On an Intel SE440BX-2 the Chassis Intrusion header is
+connected to a normally open switch.
+
+The ADM9240 provides an internal open drain on this line, and may output
+a 20 ms active low pulse to reset an external Chassis Intrusion latch.
+
+Clear the CI latch by writing value 1 to the sysfs chassis_clear file.
+
+Alarm flags reported as 16-bit word
+
+ bit label comment
+ --- ------------- --------------------------
+ 0 +2.5 V_Error high or low limit exceeded
+ 1 VCCP_Error high or low limit exceeded
+ 2 +3.3 V_Error high or low limit exceeded
+ 3 +5 V_Error high or low limit exceeded
+ 4 Temp_Error temperature error
+ 6 FAN1_Error fan low limit exceeded
+ 7 FAN2_Error fan low limit exceeded
+ 8 +12 V_Error high or low limit exceeded
+ 9 VCCP2_Error high or low limit exceeded
+ 12 Chassis_Error CI pin went high
+
+Remaining bits are reserved and thus undefined. It is important to note
+that alarm bits may be cleared on read, user-space may latch alarms and
+provide the end-user with a method to clear alarm memory.