hypothetical: more return stack levels on 11C, 15C, 16C

[brouhaha]

Thanks for your comments, Valentin! I think you're probably right, that there is little point to enlarging the subroutine stack. I brought it up because it would be fairly easy to do, but I wasn't sure whether anyone would have a use for it.

I could just as easily _reduce_ the size of the return stack, but I'm reasonably confident that no one wants that.
:-)

All of my microcode 15C and 16C changes so far have remained compatible with the original Voyager hardware, aside from needing more memory. At one point I put together an ugly kludge to patch the ROM of an original 15C, and add RAM.

Now that the calculators are ARM-based, I could do modifications beyond that, e.g. adding custom Nut instructions. If anyone wanted a really large return stack, to support recursion (but not needed for tail recursion), it could be done in that way with negligible performance penalty. I doubt that anyone will especially want that either.

Anyhow, it's been interesting contemplating the idea.