softcore for learning purposes

[brucehoult]

LC3 doesn't have opcode space to add more. There is only one free major opcode.

Subtraction can be handled by taking the 2s complement and adding.  Slide 5-10 on page 3 here:

https://www.cis.upenn.edu/~milom/cse240-Fall05/handouts/Ch05.pdf

Sure. I covered synthesizing SUB, OR, XOR from first principles back in...

https://www.eevblog.com/forum/fpga/softcore-for-learning-purposes/msg3270124/#msg3270124

I showed how to fake up shifts a few posts later.