Breakpoints

Debugging is hard. It would easier with breakpoints. But breakpoints need to be implemented. How?

Well, I can use a RST vector. Say RST 20H.

If I'm running from RAM, I can replace the first byte of all instructions at a break location with RST 20H and then start executing. Then when that's called, go into breakpoint mode. In breakpoint mode, I need to make the following commands available:
set break point (addr)
reset break point (bp #)
run
write register (including sp and pc)
dump registers
dump mem (addr len)

I should also have support in the UART to go into breakpoint mode from inside getchar().

Step is just where you put a breakpoint on either the next assembly instruction or the first assembly instruction of the next C line, then erase it when done. In the case of conditional branches and returns, it's a little tricker because they require either 2 breakpoints or evaluation of the condition flag to know where to put the next instruction. Also jp (hl) needs to be managed.

I just have to figure out how to use sdgdb..... Either that or make my own source debugger....