Low Level Debugger


The low level debugger is a single step utility that uses the trace bit on 68K/Coldfire CPUs or the T1 interrupt in 8031 CPUs. It steps through machine instructions one at a time or many at a time, like a simulator. The debugger has its own thread, but you have to be careful what the code modifies. This utility is mostly useful for debugging compute-intensive algorithms.

The Forth way is to factor out the slow part into words that are so simple you don't need a debugger like this. But, this kind of thing is a nice learning tool and sometimes you really need raw speed. LOBUG.G is the source for the debugger.


Table TR1. Key usage
F1 Help screen
F2 Toggle browse/edit (white = editable)
F5 Upload from target memory
Enter Accept edited field
ESC Done
^C copy to clipboard
[S]tep Run until PC points to the next line
[I]nto Execute one instruction
[G]o Run until breakpoint (blue).
a[N]imate Does [I]nto until a key is pressed.
Click Place breakpoint or set cursor
Double click Place PC or browse tokens

TRACE OVER brought up this screen:

It's fairly simple to use, but not very forgiving of mistakes. Here are some caveats to avoid crashes: