After a year away from the project (we adopted a puppy and then there’s been a pandemic), I got back into it today and picked up where I left off in 2019. I’d realized that the stack instructions had been forgotten, so I implemented the rest of those (16-bit and both varieties of 8-bit pushes and pops).

There’s 36 words left in the control store at this point, which may make fitting syscall in hard and leaves basically no space for future expansion using the control store write functionality. Once syscall is implemented (and maybe after some other cleanup is done) I want to go back and see if I can optimize some of the microcode, both to speed it up and save some space. If I can’t free up any significant amount of space I may have to look at expanding the control store address bus to 10 bits wide instead of the current 9.

Next up is implementing the last instruction, syscall, then the instruction set should be completely implemented. I’m sure I’ll run across missing things when I start writing actual code for the system, but I can implement things as needed later on.