After a lot of hair pulling, we just figured out a pretty serious bug in the C542 BSP/auto-buffering unit transmitter. While the docs state that ABU will work fine with periods of IDLE3 power saving, we found that our data was coming out doubled, or duplicated. E.g. ABCD in the ABU RAM buffer would come out of the BSP as AABBCCDD. Apparently something does not properly wake up and update the AXR pointer every time.
The problem seems to go away when we use IDLE1 or IDLE2.
I know this is an old design/chip, but I wanted to post something in case anyone else is still using it and has a similarly annoying experience.
MPD