The Motorola DSP56156 that's used in Konami's Polygonet Commanders and Polynet Warriors is *very* close to doing what it should. I ran out of time years ago to finish it off. The code is in a really weird state right now though. I was trying to do some abstractions in 2010 that modern C++ probably do much more easily.
The specific CPU can be a little frustrating working with because the documentation can be off in parts, but there *is* plenty of documentation, a few documentation addendum, and a win16 simulator for it, that can all be referenced. I wrote some python scripts that would exercise the simulator in ways that MAME exercised the core as well. It should be a fun project.
The MAME CPU core is communicating with the main CPU well enough to upload a bunch of 3d model data to the right spots - the dsp56156 just isn't grinding through its calculations yet. (see post here called "Polygonz attack" - https://mameworld.info/ajg/
). If i remember right, it's getting stuck in a loop because i don't emulate one of the loop instructions right? Hard to recall.
I can try to dig up all the junk I have that would help in its emulation, if you're curious.