[Coco] xroar host debugger project?

[Ciaran Anscomb]

Joel Rees via Coco wrote:
> This is primarily for Ciaran, but I'm wondering if anyone else has
> thought about adding a built-in debugging interface to xroar, either a
> front-panel style interface or a host command-line style interface.

Only in a "it would probably be nice..." way myself.  The reason for
me adding the GDB interface in the first place was that someone else
had expressed interest in developing an external tool to visualise
such things, and GDB stub as a protocol seemed like the obvious way to
expose things.  Patching GDB itself wasn't too much effort at the time
(though everything's changed since then).

> I'm trying to get a dumb transliteration of VTL-2 (6801) running on
> the Color Computer, and I'm needing to look at the list of program
> lines in memory after a line insertion, and poking stuff to the screen
> has limits. And I'm not seeing how to do this on gdb remote, which is
> probably my lack of experience with gdb.

Is the "disassemble" command enough?

https://visualgdb.com/gdbreference/commands/disassemble

# Start XRoar with GDB stub enabled (default localhost:65520)

$ xroar -gdb &
[...]

# Connect m6809-gdb to XRoar

$ m6809-gdb 
[...]
(gdb) target remote localhost:65520
Remote debugging using localhost:65520
0x0000bbca in ?? ()
(gdb) disassemble /r 0x8000,+16
Dump of assembler code from 0x8000 to 0x8010:
   0x00008000:  7e bb 3c        jmp     $bb3c
   0x00008003:  7e bb 88        jmp     $bb88
   0x00008006:  7e bb e5        jmp     $bbe5
   0x00008009:  7e bb b5        jmp     $bbb5
   0x0000800c:  7e bc ab        jmp     $bcab
   0x0000800f:  7e bd 1a        jmp     $bd1a

You can also type "layout asm" and it'll divide the screen showing a
disassembly from the current PC above the interactive area.

Most of the basic assembly-level functionality of GDB seems to work,
eg watch for writes to the first byte of text screen memory:

(gdb) watch *((char *)0x0400)
Hardware watchpoint 1: *((char *)0x0400)
(gdb) c
Continuing.

(then say clear the screen...)

Program received signal SIGTRAP, Trace/breakpoint trap.
0x0000ba80 in ?? ()

..ciaran