proper under voltage detection (F3.2)

[hackinistrator]

i made a simple test to see if the board will detect under voltage events on duet3 .12V supply with high resistance wires , moving large steppers fast .

the only under voltage shown is for the 12V rail , not the main supply .
M122 :

Supply voltage: min 9.6, current 11.2, max 13.1, under voltage events: 0, over voltage events: 0, power good: yes
12V rail voltage: min 9.2, current 10.5, max 12.3, under voltage events: 11

under voltage on main supply never recorded . when i tried to generate higher under voltage event the board will reset itself .
i think the limit for under voltage on the main supply should be changed a bit higher .

[dc42]

The 12V rail is the one that is critical to keep the drivers working on Duet 3, so that's the one that generates under-voltage events.