DevGuide/GDB OpenOCD Debug

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Commands can often be issued without typing the entire command. Here are some commonly used commands; many of them can be invoked using only the first letter:

(gdb) quit – exit the debugger
(gdb) file – load an executable file
(gdb) break line-number/function name -- Set a break-point on a line/at start of function
(gdb) run <args> -- start running the program; if there are command-line arguments, put them after the run invocation
(gdb) cont -- continue running, after a break
(gdb) next -- Next program line (step over function calls)
(gdb) step -- Step into function calls.
(gdb) finish - Step out of the present function
(gdb) print expression -- Show value of a variable or expression
(gdb) list – List 10 lines of the program being debugged. The sixth line is the preset statement. Subsequent, consecutive entry of list will list the next 10 lines.
(gdb) where – obtain a backtrace showing all function calls before the current statement
(gdb) up – Move to the function that called the present function. Useful if your program crashes in a library function; use up to get to the last function call in your program
(gdb) down – Reverses the action of up
(gdb) delete – Removes breakpoint by number (see example following). If no number, all deleted.
(gdb) kill – Terminates the program.

GDB - OpenOCD - Floss JTAG

Connecting OpenOCD to a Floss JTAG (Lisa/L in this case) an GDB to OpenOCD.

  1. Start openocd in a new shell since this process needs to remain running.
    • STM targets
    To connect to the Lisa/L board run the command
    openocd -f interface/lisa-l.cfg -f board/lisa-l.cfg
    To connect to the Lisa/M board via FLOSS-JTAG run the command:
    openocd -f interface/flossjtag.cfg -f board/lisa-l.cfg
    • NXP LPC targets
    To connect to the LPC based board via OLIMEX ARM-USB-OCD dongle run the command:
    openocd -f interface/olimex-arm-usb-ocd.cfg -f target/lpc2148.cfg
    To connect to the LPC based board via OLIMEX ARM-USB-OCD-H dongle run the command:
    openocd -f interface/olimex-arm-usb-ocd-h.cfg -f target/lpc2148.cfg
  1. Compiler Debug Options
    On LPC target build your ap file with debug options. See .
  1. Start GDB with an argument of the elf file created and uploaded to the board.
    If you programmed with the ap target then the command would be along the lines of
    /opt/paparazzi/arm-multilib/bin/arm-none-eabi-gdb var/<airframe>/ap/ap.elf
    Replace <airframe> with the name of the airframe that has been built.
  1. Now connect GDB to the board
    target remote localhost:3333
  2. Now we need to set some break points in the code.
    In this example the ap target was part of the rotorcraft and main.c contains the main program. Open rotorcraft sw/airborne/firmwares/rotorcraft/main.c and find a line at which you'd like to set a break point.
    break main.c:113
  3. Stop the currently running code
    monitor reset halt
  4. Reset the code back to the start
    monitor reset init
  5. Now we can run the program which will stop at the break point we set.

Black Magic Probe specific

  1. Start GDB for arm
    Open GDB with the correct binary file
    /opt/paparazzi/arm-multilib/bin/arm-none-eabi-gdb ./var/AIRFRAME/ap/ap.elf
    Set Black Magic Probe as Target over the serial link (see ls /dev/ttyACM*):
    target extended-remote /dev/ttyACM0
    Probe via JTAG to get a list of devices:
    mon jtag_scan
    (for Lisa/S, use swdp_scan instead of jtag_scan)
    Attach to a device:
    attach 1
  2. Happy Debugging!

Useful GDB commands

Also look at DevGuide/GDB_OpenOCD_Debug#GDB for general GDB commands

To display some commands for BMP

monitor help

example output fot STM32F4

General commands:
	version -- Display firmware version info
	help -- Display help for monitor commands
	jtag_scan -- Scan JTAG chain for devices
	swdp_scan -- Scan SW-DP for devices
	targets -- Display list of available targets
	morse -- Display morse error message
	connect_srst -- Configure connect under SRST: (enable|disable)
ARM Cortex-M specific commands:
	vector_catch -- Catch exception vectors
STM32F4 specific commands:
	erase_mass -- Erase entire flash memory
	option -- Manipulate option bytes

  • We probably want to ignore the interrupt calls for the moment so we can step through the code as it's being called. Note that we don't always want to do this. (STM32 command only)
    monitor cortex_m3 maskisr on
  • A stack trace can be printed with the command
  • show the variable of a variable
    print i2c1.status
  • Show (eXamine) the value of the 9 bytes hardware register at address 0x40005800 and show them in hex format:
    x/9x 0x40005800
  • In some cases you may not be able to access some memory areas in the mcu, in that case you should try:
    set mem inaccessible-by-default off

.gdbinit for BMP

The standard commands like setting the ttyACM0 port, searching for targets and attaching one can be automated. Either with a ".gdbinit" file or if your work with Eclipse, there is a box at Debug configutations/Startup.

One Example from armstrap

target extended-remote /dev/ttyACM0
mon swdp_scan
attach 1
monitor vector_catch disable hard
set mem inaccessible-by-default off
set print pretty

Setting up .gdbinit for BMP and gdb-regview

If you use gdb just with a BMP, you can set some initialization commands in ~/.gdbinit that will run when gdb is started, improving workflow.

A very useful plug-in called gdb-regview (available on GitHub) can really speedup debugging stm32 processors by providing a pretty-printed summary of register contents.

A sample file for debugging Lisa/M 2.0 would be:

set target-async on
set mem inaccessible-by-default off
#for gdb-regview plugin
source /path/to/gdb-regview/
regview load /path/to/gdb-regview/defs/STM32F10X_CL.xml
tar ext /dev/BMP_DEVICE
mon version
mon swdp_scan
att 1

This should be saved in ~/.gdbinit.

Then, after one starts gdb as described above, you can view registers easily, for example:

(gdb) regview show ADC_CR1

Load new binary from gdb with BMP

It is also easy to rebuild and reload a program from inside gdb. Calling make from the gdb command line will call make in your current directory:

(gdb) make

To load a new elf file into gdb after compiling elsewhere (only required when changing the name of the file):

(gdb) file file_name.elf

To upload the binary as per the currently loaded elf:

(gdb) load

This assumes you have attached to the target already (as per the .gdbinit example just above).

To restart the program from the beginning:

(gdb) run

and enter y.

gdb should detect that the elf has changed when loading the new binary, so if the file name has not changed, one should just be able to rebuild (make from inside gdb if appropriate) and then call load and run.