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# Sensor Config
This program is only meant to control fans given thermal sensor readings.
All sensors in phosphor-dbus-interfaces for OpenBMC use Sensor.Value as their
accessor. This provides read-only access to information. The goal of the
configuration is to specify how it can be read and if it's a fan, how the PID
output can be written. Initially there'll only be sysfs and passive dbus
access. If a writePath for a sensor is a dbus path, then the system will need
to verify which Control.Fan* interfaces is registered and send values to the
Target property of that interface.
The min/max specified are to range a writePercent to the sensor. The current
FanController object outputs the new fan speed goal as a PWM percentage. Other
fan PID control objects may not, and they can leave the fields as 0 & 0.
The only requirement for a sensor is that it isn't writeonly. Only fans are
expected to have a writePath set, and in this current version non-fan sensors
are assumed readonly.
The sensor names are unique across all zones.
"sensors" : [
{
"name": "fan1", /* Name of the sensor. */
"type": "fan", /* Type of sensor, fan, temp, margin */
"readPath": "", /* How the sensor can be read[1] */
"writePath": "", /* How the sensor can be set[2] */
"min": 0, /* The minimum value used for scaling writes (int64) */
"max": 255, /* The maximum value used for scaling writes (int64) */
"timeout": 0 /* The timeout value for the sensor, used for failsafe, 0
* means no timeout (int64) */
},
]
[1] readPath has multiple options:
* If it has "/xyz/openbmc_project/extsensors/" in it, it's an EXTERNAL or
host-provided sensor.
* If it has "/xyz/openbmc_project/" in it, it's a sensor whose value is
received passively over dbus.
* If it has "/sys/" in it, it's a sensor read directly from sysfs.
[2]
* This can be left blank if the sensor is read-only.
* If it has "/sys/" in it, it's a sensor written to sysfs.
* If min and max are non-zero, it'll convert the value to within the range.
and output that modified value. So, if it receives a value of .90 and min
is 0, and max is 255, it'll convert that to a value of 229.5 that is then
cast to int64_t.
# PID Config
The PID configuration is a list of PIDs per zone.
"zones" : [
{
"id": 1, /* zone id. */
"minThermalRpm": 3000.0, /* The minimum thermal RPM value. (double) */
"failsafePercent": 75.0, /* The percent to use when the zone is in fail-safe mode. (double) */
"pids": [
{
"name": "fan1-5", /* PID name */
"type": "fan", /* Type of PID, fan, temp, or margin. */
"inputs": ["fan1", "fan5"], /* Sensor names that are inputs for the PID */
"setpoint": 90.0, /* For temp/margin PIDs this is the setpoint, ignored otherwise (double) */
"pid": {
"samplePeriod": 0.1, /* The input sample period. (double) */
"proportionalCoeff": 0.0, /* The proportional coefficient. (double) */
"integralCoeff": 0.0, /* The integral coefficient. (double) */
"feedFwdOffsetCoeff": 0.0, /* The feed-forward offset coefficient. (double) */
"feedFwdGainCoeff": 0.010, /* The feed-forward gain coefficient. (double) */
"integralLimit_min": 0.0, /* The integral limit clamp, min, max (double) */
"integralLimit_max": 0.0,
"outLim_min": 30.0, /* the PID output clamp, min, max (double) */
"outLim_max": 100.0,
"slewNeg": 0.0, /* The slew negative value. (double) */
"slewPos": 0.0 /* The slew positive value. (double) */
}
}
]
}
]