MEGA65/m65dbg

An enhanced remote serial debugger/monitor for the mega65 project

m65dbg

The “m65dbg” tool is a command-line based enhanced remote serial debugger/monitor for the mega65 project. In brief, some of its facilities include:

• Capable of being a symbolic debugger (for code compiled with Ophis, ACME or CC65)
• Disassemble any point of memory (showing original file-listing, if available)
• Print out memory values in byte, word, dword or string form
• Watch such memory values continuously as you debug and step through code
• Save and load chunks of memory between the MEGA65 and your local PC
• Provide a backtrace that you can comfortably move up and down through
• Search through memory for a sequence of bytes or string
• Take petscii screenshots of current screen context (borrowed from m65 tool)
• Remote-typing mode (borrowed from m65 tool)
• FTP access to SD-card (borrowed from mega65_ftp tool)
• You can also connect m65dbg to the serial-monitor provided by the xemu mega65 emulator

Latest documentation

Latest detailed documentation can be found here:

• https://docs.google.com/document/d/1cEhHvvc1E47UgSoXvKPpwnf43l20sLPY-y-ZuQ4b_ng/edit

The raw monitor

The m65dbg app adds enhanced commands on-top of the existing commands provided by the raw monitor.

Documentation for this raw monitor exists for it in the following locations:

• The MEGA65 Compendium: https://mega65.org/docs
• C65GS System Notes
  • https://docs.google.com/document/d/1fmEUg6hDdWRb2tFZ3n4LG7S1mNP04_SUAW5DrE8zRpk/edit#
  • See the “4.3 Remote Serial Monitor (handy for debugging)” section
• https://github.com/Ben-401/c65gs/blob/dockit/doc/monitor.md
  • Some extra usage info exists in this page of Ben's fork of the github repo
• Typing “?” within the monitor (via your terminal app) to see a list of slightly outdated commands

The source for the m65dbg app is available here:

• https://github.com/MEGA65/m65dbg

Video walkthroughs of m65dbg

These videos are highly-recommended watching, in order to get quickly acquainted with the facilities available in the m65dbg tool:

• m65dbg walkthrough
  • https://www.youtube.com/watch?v=2VT8yB3odhg
• m65dbg updates
  • https://www.youtube.com/watch?v=Rumti6AzsKY

For a youtube video walkthrough, please visit:

• https://www.youtube.com/watch?v=2VT8yB3odhg

Walkthrough

Here's some written points below:

• Should build fine in Windows+Cygwin and Linux.
• Mac OSX presently doesn't support the 2,000,000 bps serial speed. So as an alternative, you can make m65dbg instead talk to the xemu mega65 emulator via a unix socket.
  • More info at:
• Specify your serial port with the "-l" (or "--device) parameter, E.g., "m65dbg -l /dev/ttyUSB1"

Try the following steps:

• ./m65dbg -l /dev/ttyUSB1
• r (to print out current registers)
• b = a raw command to set a hardware breakpoint
• t1 (to turn trace mode on, a bit like ctrl-c breaking inside gdb)
• t0 (to turn trace mode off, a bit like doing 'c'/continue in gdb)
• n (my 'next'/step-over command, which uses the hardware's step-into command multiple times, can be very slow)
• s (my 'step-into' command, which just calls the hardware's step-into)
• [ENTER] key will repeat the last command
• finish (my 'step-out-of' command, which calls 'n'/next multiple times, can be very slow, depending on how busy the current function is)
• pb/pw/pd/ps = prints byte/word/dword/string values at the given address
• typing “help” will give you the list of m65dbg commands, while typing “?” will give you the list of raw commands.