DEPENDENCIES

• GNU ARM compilation toolchain.
• Cross-compiled GDB for ARM.
• Ruby interpreter.

DIRECTORIES

• src/preloader: Simple stager payload to speed up the debugger injection.
• src/qcombbdbg: Debugger sources.
• scripts/tools/dbgupload.rb: Uploads the debugger into volatile memory.
• scripts/tools/gdbproxy.rb: Proxy to interface GDB with the live debugger.

SUPPORTED DEVICES

• Option Icon 225, firmware revision 2.5.13Hd
• Option Icon 225, firmware revision 2.5.21Hd
• Option Icon 225, firmware revision 2.5.23Hd

USAGE

1. Compile preloader.bin and qcombbdbg.bin images (e.g make MODEL=2.5.13Hd).
2. Plug the USB stick, 3 emulated serial ports should appear (under Linux, requires the hso module).
3. Go to scripts/tools and run: ruby dbgupload.rb /dev/ttyHS2
4. On success, run: ruby gdbproxy.rb tcp:1234 tty:/dev/ttyHS2
5. Fire GDB, and load the .gdbinit file provided in the root folder.
6. Type: connect 1234, GDB will connect to the proxy and will import the list of threads.

RANDOM NOTES

This is still very experimental.

REX creates a fake idle task named 'REX Idle Task' (Task #1). This task is actually never scheduled, so you cannot break it, nor step into it. The real idle task is called 'SLEEP'. At startup, GDB will automatically attach to a thread and stop it. The debugger forces GDB to attach to the fake idle task, so the system will still be fully running.

In non-stop mode, GDB will execute commands in the current thread context. If you want to change the current thread, use the command thread <num>. The first thing you might want to do is to interrupt the watchdog task.

For example:

   (gdb) thread find DOG
   Thread 68 has extra info 'DOG           [wait: 0x00006800; active: 0x00000000]'
   
   (gdb) thread apply 68 interrupt
   Thread 68 (Thread 68):
   [Thread 68] #68 stopped.
 

Displaced stepping is disabled for the moment (as of GDB 7.3.1, Thumb is not supported). Consequently, do not try to single-step or put breakpoints into heavily used system functions (like memcpy, rex_wait, rex_set_signals, and so on). If the DIAG task or the USB task encounters an exception, the debugger won't be able to handle it.