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![Jean Delvare](/assets/img/avatar_default.png)
Let the user select the base PWM frequency when using the it87 hardware monitoring driver. Different frequencies can give better control on some fans. Also update the documentation to mention the PWM frequency control files, with misc cleanups to the PWM section. Signed-off-by: Jean Delvare <khali@linux-fr.org>
400 lines
12 KiB
Text
400 lines
12 KiB
Text
Naming and data format standards for sysfs files
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------------------------------------------------
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The libsensors library offers an interface to the raw sensors data
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through the sysfs interface. See libsensors documentation and source for
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further information. As of writing this document, libsensors
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(from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
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support for any given chip requires modifying the library's code.
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This is because libsensors was written for the procfs interface
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older kernel modules were using, which wasn't standardized enough.
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Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
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support for the sysfs interface, though.
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The new sysfs interface was designed to be as chip-independent as
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possible.
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Note that motherboards vary widely in the connections to sensor chips.
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There is no standard that ensures, for example, that the second
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temperature sensor is connected to the CPU, or that the second fan is on
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the CPU. Also, some values reported by the chips need some computation
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before they make full sense. For example, most chips can only measure
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voltages between 0 and +4V. Other voltages are scaled back into that
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range using external resistors. Since the values of these resistors
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can change from motherboard to motherboard, the conversions cannot be
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hard coded into the driver and have to be done in user space.
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For this reason, even if we aim at a chip-independent libsensors, it will
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still require a configuration file (e.g. /etc/sensors.conf) for proper
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values conversion, labeling of inputs and hiding of unused inputs.
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An alternative method that some programs use is to access the sysfs
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files directly. This document briefly describes the standards that the
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drivers follow, so that an application program can scan for entries and
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access this data in a simple and consistent way. That said, such programs
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will have to implement conversion, labeling and hiding of inputs. For
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this reason, it is still not recommended to bypass the library.
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If you are developing a userspace application please send us feedback on
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this standard.
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Note that this standard isn't completely established yet, so it is subject
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to changes. If you are writing a new hardware monitoring driver those
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features can't seem to fit in this interface, please contact us with your
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extension proposal. Keep in mind that backward compatibility must be
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preserved.
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Each chip gets its own directory in the sysfs /sys/devices tree. To
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find all sensor chips, it is easier to follow the device symlinks from
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/sys/class/hwmon/hwmon*.
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All sysfs values are fixed point numbers.
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There is only one value per file, unlike the older /proc specification.
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The common scheme for files naming is: <type><number>_<item>. Usual
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types for sensor chips are "in" (voltage), "temp" (temperature) and
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"fan" (fan). Usual items are "input" (measured value), "max" (high
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threshold, "min" (low threshold). Numbering usually starts from 1,
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except for voltages which start from 0 (because most data sheets use
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this). A number is always used for elements that can be present more
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than once, even if there is a single element of the given type on the
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specific chip. Other files do not refer to a specific element, so
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they have a simple name, and no number.
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Alarms are direct indications read from the chips. The drivers do NOT
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make comparisons of readings to thresholds. This allows violations
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between readings to be caught and alarmed. The exact definition of an
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alarm (for example, whether a threshold must be met or must be exceeded
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to cause an alarm) is chip-dependent.
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-------------------------------------------------------------------------
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[0-*] denotes any positive number starting from 0
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[1-*] denotes any positive number starting from 1
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RO read only value
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RW read/write value
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Read/write values may be read-only for some chips, depending on the
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hardware implementation.
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All entries are optional, and should only be created in a given driver
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if the chip has the feature.
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************
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* Voltages *
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************
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in[0-*]_min Voltage min value.
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Unit: millivolt
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RW
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in[0-*]_max Voltage max value.
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Unit: millivolt
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RW
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in[0-*]_input Voltage input value.
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Unit: millivolt
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RO
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Voltage measured on the chip pin.
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Actual voltage depends on the scaling resistors on the
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motherboard, as recommended in the chip datasheet.
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This varies by chip and by motherboard.
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Because of this variation, values are generally NOT scaled
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by the chip driver, and must be done by the application.
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However, some drivers (notably lm87 and via686a)
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do scale, because of internal resistors built into a chip.
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These drivers will output the actual voltage.
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Typical usage:
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in0_* CPU #1 voltage (not scaled)
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in1_* CPU #2 voltage (not scaled)
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in2_* 3.3V nominal (not scaled)
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in3_* 5.0V nominal (scaled)
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in4_* 12.0V nominal (scaled)
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in5_* -12.0V nominal (scaled)
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in6_* -5.0V nominal (scaled)
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in7_* varies
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in8_* varies
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cpu[0-*]_vid CPU core reference voltage.
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Unit: millivolt
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RO
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Not always correct.
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vrm Voltage Regulator Module version number.
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RW (but changing it should no more be necessary)
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Originally the VRM standard version multiplied by 10, but now
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an arbitrary number, as not all standards have a version
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number.
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Affects the way the driver calculates the CPU core reference
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voltage from the vid pins.
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Also see the Alarms section for status flags associated with voltages.
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********
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* Fans *
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********
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fan[1-*]_min Fan minimum value
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Unit: revolution/min (RPM)
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RW
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fan[1-*]_input Fan input value.
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Unit: revolution/min (RPM)
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RO
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fan[1-*]_div Fan divisor.
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Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
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RW
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Some chips only support values 1, 2, 4 and 8.
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Note that this is actually an internal clock divisor, which
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affects the measurable speed range, not the read value.
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Also see the Alarms section for status flags associated with fans.
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*******
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* PWM *
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*******
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pwm[1-*] Pulse width modulation fan control.
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Integer value in the range 0 to 255
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RW
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255 is max or 100%.
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pwm[1-*]_enable
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Switch PWM on and off.
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Not always present even if pwmN is.
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0: turn off
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1: turn on in manual mode
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2+: turn on in automatic mode
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Check individual chip documentation files for automatic mode
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details.
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RW
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pwm[1-*]_mode 0: DC mode (direct current)
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1: PWM mode (pulse-width modulation)
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RW
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pwm[1-*]_freq Base PWM frequency in Hz.
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Only possibly available when pwmN_mode is PWM, but not always
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present even then.
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RW
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pwm[1-*]_auto_channels_temp
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Select which temperature channels affect this PWM output in
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auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
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Which values are possible depend on the chip used.
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RW
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pwm[1-*]_auto_point[1-*]_pwm
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pwm[1-*]_auto_point[1-*]_temp
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pwm[1-*]_auto_point[1-*]_temp_hyst
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Define the PWM vs temperature curve. Number of trip points is
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chip-dependent. Use this for chips which associate trip points
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to PWM output channels.
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RW
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OR
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temp[1-*]_auto_point[1-*]_pwm
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temp[1-*]_auto_point[1-*]_temp
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temp[1-*]_auto_point[1-*]_temp_hyst
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Define the PWM vs temperature curve. Number of trip points is
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chip-dependent. Use this for chips which associate trip points
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to temperature channels.
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RW
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****************
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* Temperatures *
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****************
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temp[1-*]_type Sensor type selection.
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Integers 1 to 6 or thermistor Beta value (typically 3435)
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RW
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1: PII/Celeron Diode
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2: 3904 transistor
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3: thermal diode
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4: thermistor (default/unknown Beta)
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5: AMD AMDSI
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6: Intel PECI
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Not all types are supported by all chips
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temp[1-*]_max Temperature max value.
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Unit: millidegree Celsius (or millivolt, see below)
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RW
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temp[1-*]_min Temperature min value.
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Unit: millidegree Celsius
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RW
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temp[1-*]_max_hyst
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Temperature hysteresis value for max limit.
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Unit: millidegree Celsius
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Must be reported as an absolute temperature, NOT a delta
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from the max value.
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RW
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temp[1-*]_input Temperature input value.
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Unit: millidegree Celsius
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RO
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temp[1-*]_crit Temperature critical value, typically greater than
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corresponding temp_max values.
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Unit: millidegree Celsius
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RW
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temp[1-*]_crit_hyst
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Temperature hysteresis value for critical limit.
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Unit: millidegree Celsius
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Must be reported as an absolute temperature, NOT a delta
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from the critical value.
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RW
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temp[1-4]_offset
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Temperature offset which is added to the temperature reading
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by the chip.
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Unit: millidegree Celsius
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Read/Write value.
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If there are multiple temperature sensors, temp1_* is
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generally the sensor inside the chip itself,
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reported as "motherboard temperature". temp2_* to
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temp4_* are generally sensors external to the chip
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itself, for example the thermal diode inside the CPU or
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a thermistor nearby.
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Some chips measure temperature using external thermistors and an ADC, and
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report the temperature measurement as a voltage. Converting this voltage
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back to a temperature (or the other way around for limits) requires
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mathematical functions not available in the kernel, so the conversion
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must occur in user space. For these chips, all temp* files described
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above should contain values expressed in millivolt instead of millidegree
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Celsius. In other words, such temperature channels are handled as voltage
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channels by the driver.
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Also see the Alarms section for status flags associated with temperatures.
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************
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* Currents *
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************
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Note that no known chip provides current measurements as of writing,
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so this part is theoretical, so to say.
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curr[1-*]_max Current max value
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Unit: milliampere
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RW
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curr[1-*]_min Current min value.
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Unit: milliampere
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RW
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curr[1-*]_input Current input value
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Unit: milliampere
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RO
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**********
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* Alarms *
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**********
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Each channel or limit may have an associated alarm file, containing a
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boolean value. 1 means than an alarm condition exists, 0 means no alarm.
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Usually a given chip will either use channel-related alarms, or
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limit-related alarms, not both. The driver should just reflect the hardware
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implementation.
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in[0-*]_alarm
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fan[1-*]_alarm
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temp[1-*]_alarm
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Channel alarm
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0: no alarm
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1: alarm
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RO
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OR
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in[0-*]_min_alarm
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in[0-*]_max_alarm
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fan[1-*]_min_alarm
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temp[1-*]_min_alarm
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temp[1-*]_max_alarm
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temp[1-*]_crit_alarm
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Limit alarm
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0: no alarm
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1: alarm
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RO
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Each input channel may have an associated fault file. This can be used
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to notify open diodes, unconnected fans etc. where the hardware
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supports it. When this boolean has value 1, the measurement for that
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channel should not be trusted.
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in[0-*]_input_fault
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fan[1-*]_input_fault
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temp[1-*]_input_fault
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Input fault condition
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0: no fault occured
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1: fault condition
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RO
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Some chips also offer the possibility to get beeped when an alarm occurs:
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beep_enable Master beep enable
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0: no beeps
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1: beeps
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RW
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in[0-*]_beep
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fan[1-*]_beep
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temp[1-*]_beep
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Channel beep
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0: disable
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1: enable
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RW
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In theory, a chip could provide per-limit beep masking, but no such chip
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was seen so far.
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Old drivers provided a different, non-standard interface to alarms and
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beeps. These interface files are deprecated, but will be kept around
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for compatibility reasons:
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alarms Alarm bitmask.
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RO
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Integer representation of one to four bytes.
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A '1' bit means an alarm.
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Chips should be programmed for 'comparator' mode so that
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the alarm will 'come back' after you read the register
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if it is still valid.
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Generally a direct representation of a chip's internal
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alarm registers; there is no standard for the position
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of individual bits. For this reason, the use of this
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interface file for new drivers is discouraged. Use
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individual *_alarm and *_fault files instead.
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Bits are defined in kernel/include/sensors.h.
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beep_mask Bitmask for beep.
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Same format as 'alarms' with the same bit locations,
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use discouraged for the same reason. Use individual
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*_beep files instead.
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RW
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*********
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* Other *
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*********
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eeprom Raw EEPROM data in binary form.
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RO
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pec Enable or disable PEC (SMBus only)
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0: disable
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1: enable
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RW
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