*rubber duck thread* Using the Sega CD subcpu in mode 1 is very doable but the larger problem is: what kind of tasks can we hand off to it, and are they asynchronous?

We can't run code directly off the cart from the subcpu. We can't simply make the faster cpu run the game. So it makes more sense that we'd have subroutines running on the subcpu to accelerate common operations that can be called from the MD main cpu.

But we run into a problem here. First is defining what "common operations" would really be. Since the subcpu is another 68k with a roughly 50% higher clock, it wouldn't make much sense to run very small or atomic operations on it. There is overhead in passing arguments...

... because it has to be done in shared memory. Overhead could kill the gains. We'd get more benefit from a larger, more complex function to really take advantage of that higher clock speed. This adds another layer to the problem, synchronicity.

If the MD cpu has to block (stop and wait for a result from the subcpu) we're losing a lot of potential throughput. The effect is similar the other way around in that we also waste resources on the subcpu waiting for a command from the MD.