Trouble ahead.

I really am struggling with getting this thing to single step properly, its a nightmare! The actual monitor code is pretty easy but I think I have something wrong on the stub end that means its just now working right. I have a single breakpoint that I place after the current instruction (lets ignore branchs and calls just now), and I then resume execution. The idea being that it runs a single instruction and hits the new breakpoint (however its been implemented) and jumps back into the debugger again.

The problem is, its just not working like that. Now RUN and STOP work great, so I know jumping in and out the debugger is fine, and I have tested BRK instructions as well and they are okay too. Whenever I hit a break I subtract 2 off the PC (as its moved on entry to the interrupt routine), and I can then resume again.

So far so good.... but if I drop in some more BRK's, they don't seem to be getting hit properly at all. I can't of course debug the stub either so I'm left with just looking at code. I suspect I'll need to start a new, simple project to try and figure out why its not working, as staring at code doesn't seem to help.

So heres the loop Im trying to debug, and its interesting coz aside from not doing much, it shows up several issues.

58D1 CE 15 FF    dec $FF15
58D4 A9 01            lda #$01 
58D6 A2 02            ldx #$02 
58D8 A0 03            ldy #$03 
58DA EA               nop   
58DB CA               dex   
58DC D0 FC            bne $58DA
58DE B9 00 10         lda $1000,y 
58E1 88               dey   
58E2 4C D1 58         jmp $58D1 

First, if I try and single step $58DA, the whole thing dies a horrible death. IF I try and step $58D6, then $FF15 is increased and Y is decreased to 1 (which is impossible).

Its all very odd, but there must be a logical solution - somewhere!