Add MB_PSU_SETTING command for MWOCP67

[evan-oxide]

We'll need to use the ClearFaults field of MB_PSU_SETTING to clear latched faults. I tested that field and the PowerCycle field (though we'll use the already-defined OPERATION command instead for disabling the output.)

This is part of oxidecomputer/hubris#2564.

[mkeeter]

I checked against the datasheet and this looks correct!

[hawkw]

Out of curiosity, does the MWOCP67 also honor the PMBus CLEAR_FAULTS command, or does that not work?

[evan-oxide]

Out of curiosity, does the MWOCP67 also honor the PMBus CLEAR_FAULTS command, or does that not work?

CLEAR_FAULTS might work too, but I'm preferring MB_PSU_SETTING because the datasheet makes it sound simpler to use and more certain to get the PSU working again. Quotes from the datasheet:

Sending a CLEAR_FAULTS command to the PSU shall reset all STATUS_ bits to ‘0’. CLEAR_FAULTS shall clear all STATUS commands at a given PAGE if PAGE command is supported. If the PAGE is set to FFh; all STATUS bits in all PAGEs shall be cleared..

MB_PSU_SETTING bit 6:

Clear PSU faults and latch. write 1 for clear faults and start PSU to operate if not working
due to a fault.

I want to test with an interesting fault that shuts off the output, like overtemperature, but haven't been able to yet.