sysfs-interface

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Naming and data format standards for sysfs files
------------------------------------------------

The libsensors library offers an interface to the raw sensors data
through the sysfs interface. See libsensors documentation and source for
more further information. As of writing this document, libsensors
(from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
support for any given chip requires modifying the library's code.
This is because libsensors was written for the procfs interface
older kernel modules were using, which wasn't standardized enough.
Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
support for the sysfs interface, though.

The new sysfs interface was designed to be as chip-independant as
possible.

Note that motherboards vary widely in the connections to sensor chips.
There is no standard that ensures, for example, that the second
temperature sensor is connected to the CPU, or that the second fan is on
the CPU. Also, some values reported by the chips need some computation
before they make full sense. For example, most chips can only measure
voltages between 0 and +4V. Other voltages are scaled back into that
range using external resistors. Since the values of these resistors
can change from motherboard to motherboard, the conversions cannot be
hard coded into the driver and have to be done in user space.

For this reason, even if we aim at a chip-independant libsensors, it will
still require a configuration file (e.g. /etc/sensors.conf) for proper
values conversion, labeling of inputs and hiding of unused inputs.

An alternative method that some programs use is to access the sysfs
files directly. This document briefly describes the standards that the
drivers follow, so that an application program can scan for entries and
access this data in a simple and consistent way. That said, such programs
will have to implement conversion, labeling and hiding of inputs. For
this reason, it is still not recommended to bypass the library.

If you are developing a userspace application please send us feedback on
this standard.

Note that this standard isn't completely established yet, so it is subject
to changes, even important ones. One more reason to use the library instead
of accessing sysfs files directly.

Each chip gets its own directory in the sysfs /sys/devices tree.  To
find all sensor chips, it is easier to follow the symlinks from
/sys/i2c/devices/

All sysfs values are fixed point numbers.  To get the true value of some
of the values, you should divide by the specified value.

There is only one value per file, unlike the older /proc specification.
The common scheme for files naming is: <type><number>_<item>. Usual
types for sensor chips are "in" (voltage), "temp" (temperature) and
"fan" (fan). Usual items are "input" (measured value), "max" (high
threshold, "min" (low threshold). Numbering usually starts from 1,
except for voltages which start from 0 (because most data sheets use
this). A number is always used for elements that can be present more
than once, even if there is a single element of the given type on the
specific chip. Other files do not refer to a specific element, so
they have a simple name, and no number.

Alarms are direct indications read from the chips. The drivers do NOT
make comparisons of readings to thresholds. This allows violations
between readings to be caught and alarmed. The exact definition of an
alarm (for example, whether a threshold must be met or must be exceeded
to cause an alarm) is chip-dependent.


-------------------------------------------------------------------------

************
* Voltages *
************

in[0-8]_min	Voltage min value.
		Unit: millivolt
		Read/Write
		
in[0-8]_max	Voltage max value.
		Unit: millivolt
		Read/Write
		
in[0-8]_input	Voltage input value.
		Unit: millivolt
		Read only
		Actual voltage depends on the scaling resistors on the
		motherboard, as recommended in the chip datasheet.
		This varies by chip and by motherboard.
		Because of this variation, values are generally NOT scaled
		by the chip driver, and must be done by the application.
		However, some drivers (notably lm87 and via686a)
		do scale, with various degrees of success.
		These drivers will output the actual voltage.

		Typical usage:
			in0_*	CPU #1 voltage (not scaled)
			in1_*	CPU #2 voltage (not scaled)
			in2_*	3.3V nominal (not scaled)
			in3_*	5.0V nominal (scaled)
			in4_*	12.0V nominal (scaled)
			in5_*	-12.0V nominal (scaled)
			in6_*	-5.0V nominal (scaled)
			in7_*	varies
			in8_*	varies

cpu[0-1]_vid	CPU core reference voltage.
		Unit: millivolt
		Read only.
		Not always correct.

vrm		Voltage Regulator Module version number. 
		Read only.
		Two digit number, first is major version, second is
		minor version.
		Affects the way the driver calculates the CPU core reference
		voltage from the vid pins.


********
* Fans *
********

fan[1-3]_min	Fan minimum value
		Unit: revolution/min (RPM)
		Read/Write.

fan[1-3]_input	Fan input value.
		Unit: revolution/min (RPM)
		Read only.

fan[1-3]_div	Fan divisor.
		Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
		Some chips only support values 1, 2, 4 and 8.
		Note that this is actually an internal clock divisor, which
		affects the measurable speed range, not the read value.

fan[1-3]_pwm	Pulse width modulation fan control.
		Integer value in the range 0 to 255
		Read/Write
		255 is max or 100%.

fan[1-3]_pwm_enable
		Switch PWM on and off.
		Not always present even if fan*_pwm is.
		0 to turn off
		1 to turn on
		Read/Write


****************
* Temperatures *
****************

temp[1-3]_type	Sensor type selection.
		Integers 1, 2, 3 or thermistor Beta value (3435)
		Read/Write.
		1: PII/Celeron Diode
		2: 3904 transistor
		3: thermal diode
		Not all types are supported by all chips

temp[1-4]_max	Temperature max value.
		Unit: millidegree Celcius
		Read/Write value.

temp[1-3]_min	Temperature min value.
		Unit: millidegree Celcius
		Read/Write value.

temp[1-3]_max_hyst
		Temperature hysteresis value for max limit.
		Unit: millidegree Celcius
		Must be reported as an absolute temperature, NOT a delta
		from the max value.
		Read/Write value.

temp[1-4]_input Temperature input value.
		Unit: millidegree Celcius
		Read only value.

temp[1-4]_crit	Temperature critical value, typically greater than
		corresponding temp_max values.
		Unit: millidegree Celcius
		Read/Write value.

temp[1-2]_crit_hyst
		Temperature hysteresis value for critical limit.
		Unit: millidegree Celcius
		Must be reported as an absolute temperature, NOT a delta
		from the critical value.
		Read/Write value.

		If there are multiple temperature sensors, temp1_* is
		generally the sensor inside the chip itself,
		reported as "motherboard temperature".  temp2_* to
		temp4_* are generally sensors external to the chip
		itself, for example the thermal diode inside the CPU or
		a thermistor nearby.


************
* Currents *
************

Note that no known chip provides current measurements as of writing,
so this part is theoretical, so to say.

curr[1-n]_max	Current max value
		Unit: milliampere
		Read/Write.

curr[1-n]_min	Current min value.
		Unit: milliampere
		Read/Write.

curr[1-n]_input	Current input value
		Unit: milliampere
		Read only.


*********
* Other *
*********

alarms		Alarm bitmask.
		Read only.
		Integer representation of one to four bytes.
		A '1' bit means an alarm.
		Chips should be programmed for 'comparator' mode so that
		the alarm will 'come back' after you read the register
		if it is still valid.
		Generally a direct representation of a chip's internal
		alarm registers; there is no standard for the position
		of individual bits.
		Bits are defined in kernel/include/sensors.h.

beep_enable	Beep/interrupt enable
		0 to disable.
		1 to enable.
		Read/Write

beep_mask	Bitmask for beep.
		Same format as 'alarms' with the same bit locations.
		Read/Write

eeprom		Raw EEPROM data in binary form.
		Read only.