Sandro Ronco completely revamped the DMV driver in r31661 and implemented the bus system and the first modules - and it's amazing! Thanks Sandro!
Apart from CP/M-80, now CP/M-86 and MS-DOS 2.11 also boot.
There's a caveat with MS-DOS: It boots if there's no memory module selected, with 64K of system memory
If a memory module is inserted in slot1, the BIOS does the memory test on the bottom of the screen, then boots into MS-DOS (recognizing the added memory, see line 3) but hangs shortly after this point ...
showing a cursor below the "Command v. 2.11" message you can see in the first screenshot.
I have to end MESS with Windows Task Manager at this point.
One thing that happens uniformly across all operating systems is, that if text scrolls off the screen, the driver freezes. To replicate you simply boot into an OS and repeatedly DIR the contents of the disk. Or you leave ladder (here on CP/M-86) and DIR ...
This condition is non-lethal though, you can reset the emulation with F3 if you're in partial keyboard mode.
Sandro even put the graphics portion in, and running DEMO5 shows this colorful jumbled picture
It seems that most of the items on the To-Do list for the upd7220 driver apply here, because this showcase program for the DMV made heavy use of the features - the machine was touted as highly graphics capable.
I want to thank not only Sandro for his work on the driver but all MESS devs - when I uploaded the first files 2 1/2 years ago, a lot of this wouldn't have been possible - the bus system, slots, CPU and Floppy controller refinements (or rewrites) all came afterwards. It's brilliant!