The trace log

The trace log records the machine state before every instruction executed: the master cycle count, PC, all main and alternate registers, IX, IY, SP, the decoded flags and the raw opcode bytes. It is a ring buffer of 10 000 entries, so it always holds the last 10 000 instructions.

• F2, the toolbar F2: Trace button (its indicator turns green), or Debug ▸ Trace ▸ Enable Trace switches it on.
• Debug ▸ Trace ▸ Clear Trace empties it.
• F3, the F3: Export Trace button, or Debug ▸ Trace ▸ Export Trace… writes it to a text file, one instruction per line.
• --trace on the command line starts with it enabled.

The trace is what makes "how did we get here?" answerable after a breakpoint fires. It is also a prerequisite for stepping backwards.