I'll keep this one brief as I've already written a long post about it elsewhere (all the gory details can be found there), but I spent far too much of the weekend making an Arduino talk to the rosco_m68k as an IO expansion (i.e. mapped into IO space and communicating with the CPU over the bus).

This exposed a(nother) couple of issues with the board - IODTACK really needs to be exposed on the expansion connector, and the glue logic is a bit quick to drop DTACK when an address in IO space is no longer being strobed, but generally speaking once I'd figured those things out it went pretty well and I was able to get the Arduino to act as a simple single-register, write-only device connected to the m68k.

The timing issue probably won't affect real hardware devices, and the IODTACK issue can be easily worked around so no need to re-do any boards at the moment, though I've raised issues on GitHub to address them at some point in the future.