Board Sensor Calibration

Patrick Williams patrick at
Fri Aug 21 02:15:32 AEST 2020

On Wed, Aug 19, 2020 at 10:39:15AM -0700, Maxim Sloyko wrote:
> Hi OpenBMC!
> We would like to have a value reported by a certain sensor changed
> according to our calibration results. This is a temperature sensor and the
> calibration has nothing to do with the sensor itself -- so no need to
> change the driver or anything -- but with a sensor placement on the board.
> Basically we want to infer the temperature at a different location by
> calibrating the sensor.
> Are there any tools in OpenBMC that would allow us to add the calibration
> curve to, say, phosphor-hwmon and have it report the value different from
> the one reported by the underlying sensor? Did anybody else have to deal
> with something like this and what was your solution? Do people more
> familiar with sensor architecture have any recommendations on how best to
> handle this?
> Thank you.
> -- 
> -MS

There is work being implemented now under phosphor-virtual-sensor[1]
which is intended to cover exactly this case (among others).  We have a
similar situation where sensors need to be calibrated based on values
from one or more other sensors.  An example might be a voltage regulator
which reads high as it gets hotter.  phosphor-virtual-sensor will allow
you to forumlate a secondary sensor (the "virtual" sensor) using math
applied to one or more real sensors.

Patrick Williams
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