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Based on kernel version 3.2. Page generated on 2012-01-05 23:28 EST.

	Naming and data format standards for sysfs files
	------------------------------------------------
	
	The libsensors library offers an interface to the raw sensors data
	through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
	completely chip-independent. It assumes that all the kernel drivers
	implement the standard sysfs interface described in this document.
	This makes adding or updating support for any given chip very easy, as
	libsensors, and applications using it, do not need to be modified.
	This is a major improvement compared to lm-sensors 2.
	
	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-independent 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.
	
	Each chip gets its own directory in the sysfs /sys/devices tree.  To
	find all sensor chips, it is easier to follow the device symlinks from
	/sys/class/hwmon/hwmon*.
	
	Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
	in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
	in the hwmon "class" device directory are also supported. Complex drivers
	(e.g. drivers for multifunction chips) may want to use this possibility to
	avoid namespace pollution. The only drawback will be that older versions of
	libsensors won't support the driver in question.
	
	All sysfs values are fixed point numbers.
	
	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.
	
	When setting values of hwmon sysfs attributes, the string representation of
	the desired value must be written, note that strings which are not a number
	are interpreted as 0! For more on how written strings are interpreted see the
	"sysfs attribute writes interpretation" section at the end of this file.
	
	-------------------------------------------------------------------------
	
	[0-*]	denotes any positive number starting from 0
	[1-*]	denotes any positive number starting from 1
	RO	read only value
	WO	write only value
	RW	read/write value
	
	Read/write values may be read-only for some chips, depending on the
	hardware implementation.
	
	All entries (except name) are optional, and should only be created in a
	given driver if the chip has the feature.
	
	
	*********************
	* Global attributes *
	*********************
	
	name		The chip name.
			This should be a short, lowercase string, not containing
			spaces nor dashes, representing the chip name. This is
			the only mandatory attribute.
			I2C devices get this attribute created automatically.
			RO
	
	update_interval	The interval at which the chip will update readings.
			Unit: millisecond
			RW
			Some devices have a variable update rate or interval.
			This attribute can be used to change it to the desired value.
	
	
	************
	* Voltages *
	************
	
	in[0-*]_min	Voltage min value.
			Unit: millivolt
			RW
			
	in[0-*]_lcrit	Voltage critical min value.
			Unit: millivolt
			RW
			If voltage drops to or below this limit, the system may
			take drastic action such as power down or reset. At the very
			least, it should report a fault.
	
	in[0-*]_max	Voltage max value.
			Unit: millivolt
			RW
			
	in[0-*]_crit	Voltage critical max value.
			Unit: millivolt
			RW
			If voltage reaches or exceeds this limit, the system may
			take drastic action such as power down or reset. At the very
			least, it should report a fault.
	
	in[0-*]_input	Voltage input value.
			Unit: millivolt
			RO
			Voltage measured on the chip pin.
			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, because of internal resistors built into a chip.
			These drivers will output the actual voltage. Rule of
			thumb: drivers should report the voltage values at the
			"pins" of the chip.
	
	in[0-*]_average
			Average voltage
			Unit: millivolt
			RO
	
	in[0-*]_lowest
			Historical minimum voltage
			Unit: millivolt
			RO
	
	in[0-*]_highest
			Historical maximum voltage
			Unit: millivolt
			RO
	
	in[0-*]_reset_history
			Reset inX_lowest and inX_highest
			WO
	
	in_reset_history
			Reset inX_lowest and inX_highest for all sensors
			WO
	
	in[0-*]_label	Suggested voltage channel label.
			Text string
			Should only be created if the driver has hints about what
			this voltage channel is being used for, and user-space
			doesn't. In all other cases, the label is provided by
			user-space.
			RO
	
	cpu[0-*]_vid	CPU core reference voltage.
			Unit: millivolt
			RO
			Not always correct.
	
	vrm		Voltage Regulator Module version number. 
			RW (but changing it should no more be necessary)
			Originally the VRM standard version multiplied by 10, but now
			an arbitrary number, as not all standards have a version
			number.
			Affects the way the driver calculates the CPU core reference
			voltage from the vid pins.
	
	Also see the Alarms section for status flags associated with voltages.
	
	
	********
	* Fans *
	********
	
	fan[1-*]_min	Fan minimum value
			Unit: revolution/min (RPM)
			RW
	
	fan[1-*]_max	Fan maximum value
			Unit: revolution/min (RPM)
			Only rarely supported by the hardware.
			RW
	
	fan[1-*]_input	Fan input value.
			Unit: revolution/min (RPM)
			RO
	
	fan[1-*]_div	Fan divisor.
			Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
			RW
			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-*]_pulses	Number of tachometer pulses per fan revolution.
			Integer value, typically between 1 and 4.
			RW
			This value is a characteristic of the fan connected to the
			device's input, so it has to be set in accordance with the fan
			model.
			Should only be created if the chip has a register to configure
			the number of pulses. In the absence of such a register (and
			thus attribute) the value assumed by all devices is 2 pulses
			per fan revolution.
	
	fan[1-*]_target
			Desired fan speed
			Unit: revolution/min (RPM)
			RW
			Only makes sense if the chip supports closed-loop fan speed
			control based on the measured fan speed.
	
	fan[1-*]_label	Suggested fan channel label.
			Text string
			Should only be created if the driver has hints about what
			this fan channel is being used for, and user-space doesn't.
			In all other cases, the label is provided by user-space.
			RO
	
	Also see the Alarms section for status flags associated with fans.
	
	
	*******
	* PWM *
	*******
	
	pwm[1-*]	Pulse width modulation fan control.
			Integer value in the range 0 to 255
			RW
			255 is max or 100%.
	
	pwm[1-*]_enable
			Fan speed control method:
			0: no fan speed control (i.e. fan at full speed)
			1: manual fan speed control enabled (using pwm[1-*])
			2+: automatic fan speed control enabled
			Check individual chip documentation files for automatic mode
			details.
			RW
	
	pwm[1-*]_mode	0: DC mode (direct current)
			1: PWM mode (pulse-width modulation)
			RW
	
	pwm[1-*]_freq	Base PWM frequency in Hz.
			Only possibly available when pwmN_mode is PWM, but not always
			present even then.
			RW
	
	pwm[1-*]_auto_channels_temp
			Select which temperature channels affect this PWM output in
			auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
			Which values are possible depend on the chip used.
			RW
	
	pwm[1-*]_auto_point[1-*]_pwm
	pwm[1-*]_auto_point[1-*]_temp
	pwm[1-*]_auto_point[1-*]_temp_hyst
			Define the PWM vs temperature curve. Number of trip points is
			chip-dependent. Use this for chips which associate trip points
			to PWM output channels.
			RW
	
	temp[1-*]_auto_point[1-*]_pwm
	temp[1-*]_auto_point[1-*]_temp
	temp[1-*]_auto_point[1-*]_temp_hyst
			Define the PWM vs temperature curve. Number of trip points is
			chip-dependent. Use this for chips which associate trip points
			to temperature channels.
			RW
	
	There is a third case where trip points are associated to both PWM output
	channels and temperature channels: the PWM values are associated to PWM
	output channels while the temperature values are associated to temperature
	channels. In that case, the result is determined by the mapping between
	temperature inputs and PWM outputs. When several temperature inputs are
	mapped to a given PWM output, this leads to several candidate PWM values.
	The actual result is up to the chip, but in general the highest candidate
	value (fastest fan speed) wins.
	
	
	****************
	* Temperatures *
	****************
	
	temp[1-*]_type	Sensor type selection.
			Integers 1 to 6
			RW
			1: PII/Celeron Diode
			2: 3904 transistor
			3: thermal diode
			4: thermistor
			5: AMD AMDSI
			6: Intel PECI
			Not all types are supported by all chips
	
	temp[1-*]_max	Temperature max value.
			Unit: millidegree Celsius (or millivolt, see below)
			RW
	
	temp[1-*]_min	Temperature min value.
			Unit: millidegree Celsius
			RW
	
	temp[1-*]_max_hyst
			Temperature hysteresis value for max limit.
			Unit: millidegree Celsius
			Must be reported as an absolute temperature, NOT a delta
			from the max value.
			RW
	
	temp[1-*]_input Temperature input value.
			Unit: millidegree Celsius
			RO
	
	temp[1-*]_crit	Temperature critical max value, typically greater than
			corresponding temp_max values.
			Unit: millidegree Celsius
			RW
	
	temp[1-*]_crit_hyst
			Temperature hysteresis value for critical limit.
			Unit: millidegree Celsius
			Must be reported as an absolute temperature, NOT a delta
			from the critical value.
			RW
	
	temp[1-*]_emergency
			Temperature emergency max value, for chips supporting more than
			two upper temperature limits. Must be equal or greater than
			corresponding temp_crit values.
			Unit: millidegree Celsius
			RW
	
	temp[1-*]_emergency_hyst
			Temperature hysteresis value for emergency limit.
			Unit: millidegree Celsius
			Must be reported as an absolute temperature, NOT a delta
			from the emergency value.
			RW
	
	temp[1-*]_lcrit	Temperature critical min value, typically lower than
			corresponding temp_min values.
			Unit: millidegree Celsius
			RW
	
	temp[1-*]_offset
			Temperature offset which is added to the temperature reading
			by the chip.
			Unit: millidegree Celsius
			Read/Write value.
	
	temp[1-*]_label	Suggested temperature channel label.
			Text string
			Should only be created if the driver has hints about what
			this temperature channel is being used for, and user-space
			doesn't. In all other cases, the label is provided by
			user-space.
			RO
	
	temp[1-*]_lowest
			Historical minimum temperature
			Unit: millidegree Celsius
			RO
	
	temp[1-*]_highest
			Historical maximum temperature
			Unit: millidegree Celsius
			RO
	
	temp[1-*]_reset_history
			Reset temp_lowest and temp_highest
			WO
	
	temp_reset_history
			Reset temp_lowest and temp_highest for all sensors
			WO
	
	Some chips measure temperature using external thermistors and an ADC, and
	report the temperature measurement as a voltage. Converting this voltage
	back to a temperature (or the other way around for limits) requires
	mathematical functions not available in the kernel, so the conversion
	must occur in user space. For these chips, all temp* files described
	above should contain values expressed in millivolt instead of millidegree
	Celsius. In other words, such temperature channels are handled as voltage
	channels by the driver.
	
	Also see the Alarms section for status flags associated with temperatures.
	
	
	************
	* Currents *
	************
	
	curr[1-*]_max	Current max value
			Unit: milliampere
			RW
	
	curr[1-*]_min	Current min value.
			Unit: milliampere
			RW
	
	curr[1-*]_lcrit	Current critical low value
			Unit: milliampere
			RW
	
	curr[1-*]_crit	Current critical high value.
			Unit: milliampere
			RW
	
	curr[1-*]_input	Current input value
			Unit: milliampere
			RO
	
	curr[1-*]_average
			Average current use
			Unit: milliampere
			RO
	
	curr[1-*]_lowest
			Historical minimum current
			Unit: milliampere
			RO
	
	curr[1-*]_highest
			Historical maximum current
			Unit: milliampere
			RO
	
	curr[1-*]_reset_history
			Reset currX_lowest and currX_highest
			WO
	
	curr_reset_history
			Reset currX_lowest and currX_highest for all sensors
			WO
	
	Also see the Alarms section for status flags associated with currents.
	
	*********
	* Power *
	*********
	
	power[1-*]_average		Average power use
					Unit: microWatt
					RO
	
	power[1-*]_average_interval	Power use averaging interval.  A poll
					notification is sent to this file if the
					hardware changes the averaging interval.
					Unit: milliseconds
					RW
	
	power[1-*]_average_interval_max	Maximum power use averaging interval
					Unit: milliseconds
					RO
	
	power[1-*]_average_interval_min	Minimum power use averaging interval
					Unit: milliseconds
					RO
	
	power[1-*]_average_highest	Historical average maximum power use
					Unit: microWatt
					RO
	
	power[1-*]_average_lowest	Historical average minimum power use
					Unit: microWatt
					RO
	
	power[1-*]_average_max		A poll notification is sent to
					power[1-*]_average when power use
					rises above this value.
					Unit: microWatt
					RW
	
	power[1-*]_average_min		A poll notification is sent to
					power[1-*]_average when power use
					sinks below this value.
					Unit: microWatt
					RW
	
	power[1-*]_input		Instantaneous power use
					Unit: microWatt
					RO
	
	power[1-*]_input_highest	Historical maximum power use
					Unit: microWatt
					RO
	
	power[1-*]_input_lowest		Historical minimum power use
					Unit: microWatt
					RO
	
	power[1-*]_reset_history	Reset input_highest, input_lowest,
					average_highest and average_lowest.
					WO
	
	power[1-*]_accuracy		Accuracy of the power meter.
					Unit: Percent
					RO
	
	power[1-*]_cap			If power use rises above this limit, the
					system should take action to reduce power use.
					A poll notification is sent to this file if the
					cap is changed by the hardware.  The *_cap
					files only appear if the cap is known to be
					enforced by hardware.
					Unit: microWatt
					RW
	
	power[1-*]_cap_hyst		Margin of hysteresis built around capping and
					notification.
					Unit: microWatt
					RW
	
	power[1-*]_cap_max		Maximum cap that can be set.
					Unit: microWatt
					RO
	
	power[1-*]_cap_min		Minimum cap that can be set.
					Unit: microWatt
					RO
	
	power[1-*]_max			Maximum power.
					Unit: microWatt
					RW
	
	power[1-*]_crit			Critical maximum power.
					If power rises to or above this limit, the
					system is expected take drastic action to reduce
					power consumption, such as a system shutdown or
					a forced powerdown of some devices.
					Unit: microWatt
					RW
	
	Also see the Alarms section for status flags associated with power readings.
	
	**********
	* Energy *
	**********
	
	energy[1-*]_input		Cumulative energy use
					Unit: microJoule
					RO
	
	
	************
	* Humidity *
	************
	
	humidity[1-*]_input		Humidity
					Unit: milli-percent (per cent mille, pcm)
					RO
	
	
	**********
	* Alarms *
	**********
	
	Each channel or limit may have an associated alarm file, containing a
	boolean value. 1 means than an alarm condition exists, 0 means no alarm.
	
	Usually a given chip will either use channel-related alarms, or
	limit-related alarms, not both. The driver should just reflect the hardware
	implementation.
	
	in[0-*]_alarm
	curr[1-*]_alarm
	power[1-*]_alarm
	fan[1-*]_alarm
	temp[1-*]_alarm
			Channel alarm
			0: no alarm
			1: alarm
			RO
	
	OR
	
	in[0-*]_min_alarm
	in[0-*]_max_alarm
	in[0-*]_lcrit_alarm
	in[0-*]_crit_alarm
	curr[1-*]_min_alarm
	curr[1-*]_max_alarm
	curr[1-*]_lcrit_alarm
	curr[1-*]_crit_alarm
	power[1-*]_cap_alarm
	power[1-*]_max_alarm
	power[1-*]_crit_alarm
	fan[1-*]_min_alarm
	fan[1-*]_max_alarm
	temp[1-*]_min_alarm
	temp[1-*]_max_alarm
	temp[1-*]_lcrit_alarm
	temp[1-*]_crit_alarm
	temp[1-*]_emergency_alarm
			Limit alarm
			0: no alarm
			1: alarm
			RO
	
	Each input channel may have an associated fault file. This can be used
	to notify open diodes, unconnected fans etc. where the hardware
	supports it. When this boolean has value 1, the measurement for that
	channel should not be trusted.
	
	fan[1-*]_fault
	temp[1-*]_fault
			Input fault condition
			0: no fault occurred
			1: fault condition
			RO
	
	Some chips also offer the possibility to get beeped when an alarm occurs:
	
	beep_enable	Master beep enable
			0: no beeps
			1: beeps
			RW
	
	in[0-*]_beep
	curr[1-*]_beep
	fan[1-*]_beep
	temp[1-*]_beep
			Channel beep
			0: disable
			1: enable
			RW
	
	In theory, a chip could provide per-limit beep masking, but no such chip
	was seen so far.
	
	Old drivers provided a different, non-standard interface to alarms and
	beeps. These interface files are deprecated, but will be kept around
	for compatibility reasons:
	
	alarms		Alarm bitmask.
			RO
			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. For this reason, the use of this
			interface file for new drivers is discouraged. Use
			individual *_alarm and *_fault files instead.
			Bits are defined in kernel/include/sensors.h.
	
	beep_mask	Bitmask for beep.
			Same format as 'alarms' with the same bit locations,
			use discouraged for the same reason. Use individual
			*_beep files instead.
			RW
	
	
	***********************
	* Intrusion detection *
	***********************
	
	intrusion[0-*]_alarm
			Chassis intrusion detection
			0: OK
			1: intrusion detected
			RW
			Contrary to regular alarm flags which clear themselves
			automatically when read, this one sticks until cleared by
			the user. This is done by writing 0 to the file. Writing
			other values is unsupported.
	
	intrusion[0-*]_beep
			Chassis intrusion beep
			0: disable
			1: enable
			RW
	
	
	sysfs attribute writes interpretation
	-------------------------------------
	
	hwmon sysfs attributes always contain numbers, so the first thing to do is to
	convert the input to a number, there are 2 ways todo this depending whether
	the number can be negative or not:
	unsigned long u = simple_strtoul(buf, NULL, 10);
	long s = simple_strtol(buf, NULL, 10);
	
	With buf being the buffer with the user input being passed by the kernel.
	Notice that we do not use the second argument of strto[u]l, and thus cannot
	tell when 0 is returned, if this was really 0 or is caused by invalid input.
	This is done deliberately as checking this everywhere would add a lot of
	code to the kernel.
	
	Notice that it is important to always store the converted value in an
	unsigned long or long, so that no wrap around can happen before any further
	checking.
	
	After the input string is converted to an (unsigned) long, the value should be
	checked if its acceptable. Be careful with further conversions on the value
	before checking it for validity, as these conversions could still cause a wrap
	around before the check. For example do not multiply the result, and only
	add/subtract if it has been divided before the add/subtract.
	
	What to do if a value is found to be invalid, depends on the type of the
	sysfs attribute that is being set. If it is a continuous setting like a
	tempX_max or inX_max attribute, then the value should be clamped to its
	limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
	continuous like for example a tempX_type, then when an invalid value is
	written, -EINVAL should be returned.
	
	Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
	
		long v = simple_strtol(buf, NULL, 10) / 1000;
		v = SENSORS_LIMIT(v, -128, 127);
		/* write v to register */
	
	Example2, fan divider setting, valid values 2, 4 and 8:
	
		unsigned long v = simple_strtoul(buf, NULL, 10);
	
		switch (v) {
		case 2: v = 1; break;
		case 4: v = 2; break;
		case 8: v = 3; break;
		default:
			return -EINVAL;
		}
		/* write v to register */

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