Use MilliAmps for IPMI tool

Tanous, Ed ed.tanous at
Thu Dec 20 06:33:12 AEDT 2018

>IPMI tool is being used to probe and get the various sensor values from bmc. However, after reading through the IPMI spec there is no support for milliAmperes or milliVolts.
I'm not really sure how to came to this conclusion.  Yes, there is no "milliamp" unit in the unit codes table, but I wouldn't expect there to be given how IPMI sensor scaling works.  For linear scaling mode (which is all openbmc supports today) value scaling is set by M and B values in a type 1 SDR record.  Setting an M value of 1000 and a units flag of Volts would effectively give you "millivolts" resolution.

Another option here would be to use logarithmic scaling, which would give you better resolution in the lower end of the spectrum (especially useful in the case of millivolts).  If this is something you'd like to pursue, there's likely some people on this list that could point you to where that capability could be added.

Some sections of the IPMI spec to reference for the above

36.3 Sensor Reading Conversion Formula
36.4.2 Resolution.
43.1 SDR Type 01h, Full sensor record, bytes 25:28

There has been some effort made to make these values calculated automatically based on the maximum and minimum value readings in the DBus interface, which makes this process far less error prone.  If this kind of thing is important to you, I would highly recommend reviewing and adding your opinion to those patches.


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