This doesn't seem to be related to our problem of locking IMC, but anyway I found a funny DAC behavior for MC2 M3 DAC.

See attached, I'm giving a huge offset to the coil output filter so the coil master output (bottom left) becomes larger than 2**27~134million counts most of the time. The user model DAC output (pink on the bottom right) rails as the master out increases, and so does the IOP DAC output (green on the bottom right), but when the master output goes larger than about 2 billion, the DAC outputs flip the sign and so do VOLTMON and FAST_IMON.

If you look at the transition at around 2 billion master out (between two markers), there seems to be a range where the IOP DAC flips the sign while the user model DAC doesn't, and the IMON as well as VOLTMON drops to zero. Here the driver voltage is not following IOP DAC.