Can you elaborate on this? From there it was just a matter of defining each control line symbolically and "assembling" each microinstruction by ORing the appropriate things together"?
This is basically your decoder then?
risk-vee is a really basic (read: dumb) "common bus" design. All of the internal components of the CPU share the same 32-bit data bus. The heart of the control unit is a ROM that is 32-bits wide. Each bit is connected to one of the various things in the CPU. To make generating the microcode easier I defined a mask for each line.
Taking "move the PC to the memory address register" as an example: The register that holds the PC has an output enable line, and the memory address register has select/enable and both would need to be high. Pulling a few lines from microcode.js:
pc_read = parseBin("0000-0000 0000-0000 0000-0000 0100-0000");
mem_address_write = parseBin("0000-0000 0000-1000 0000-0000 0000-0000");
pc_read | mem_address_write