MAME debugger fails to halt on breakpoints

[fredsa]

The breakpoint handling in MAME is broken. Chasing this down, it appears this is due to MAME's src/osd/modules/debugger/none.cpp automatically resuming the CPU:

void debug_none::wait_for_debugger(device_t &device, bool firststop)
{
	m_machine->debugger().console().get_visible_cpu()->debug()->go();
}

[fredsa]

To debug this, I have a (VERY messy) working branch (https://github.com/fredsa/8bitworkshop/tree/luasandbox, currently at 0d9f7c792609986e706168c4b41449e121bdf756) that I've been using.

• It has much of the debugging code ripped out or simplified.
  • emu.pause() and emu.unpause() are not used as they uselessly pause on frame boundaries
• A debug script enables easy testing:
  • Run node test_cli.js to run
  • A hard-coded test program (presets/atari8-800/breakpoints.dasm) is run
  • Hard-coded breakpoints (debugger.lua) are applied
• debugger.lua uses cpudebug:bpset(addr, nil, action) to set breakpoints
  • the action (lua mamedbg.on_hit(addr)) is never executed
• register_periodic provides console output that shows (some of) the runtime behavior
  • Periodic callbacks aren't suitable for for breakpoint handling

Possible path to explore?

• Modify https://github.com/sehugg/mame/'s debugger to use https://emscripten.org/docs/porting/asyncify.html
  • Change none.cpp to call emscripten_sleep(…) instead of go()