So having gotten my SpamCC compiler working I then realised that perhaps it would be a better idea to start with a CHIP-8 compiler or cross-compiler.

The benefit of going after CHIP-8 is the availability of existing software, ie retro-games, and CHIP-8 is really simple with only 35 opcodes.

So I spent a few hours writing a CHIP-8 emulator to learn more about CHIP-8 and you can see the results in my github repo. 

The upshot is that I think a compiler is actually pretty feasible. 

A cross-compiler from CHIP-8 bytecode where I dont have the source is also pretty easy most of the time though there will be complications for a few games because of the way instructions are aligned in them. In CHIP-8 every instruction is 2 bytes wide and most of the time the instructions are aligned at an even memory address so it's easy to disassemble the code passing across it linearly. However, the occasional program doesn't align to even addresses so for these one would need to recursively disassemble the code by walking each of the jump operations to see where one ends up. This is feasible except for the Bxxx operation which can jump to a calculated address and this is a bit of a show stopper I think. Fortunately, I haven't  seen use of Bxxx and there are plenty of games that do align to even addresses. Also, if I can get the source for a game then that overcomes the disassembly & alignment issue entirely. 

Anyway - next step will be to map this into my Verilog simulation to see the simulated SPAM-1 running a game (slowly no doubt) and then get back to the hardware build...

PONG ...

BREAKOUT ...