# SWD GDB Hardware Debugging

This page documents how to connect the hardware target using GDB (from a terminal). To use an IDE instead, see the instructions for Eclipse or VSCode.

For the wiring interface setup, please see this detailed information: SWD/JTAG Debug Interface.

# Using Dronecode probe / Blackmagic probe


To debug STM32F7 or later (FMUv5 and newer) the Dronecode probe / Blackmagic probe likely requires a firmware update. You can find how to update the blackmagic probe here (opens new window).

To use a Dronecode probe with GDB, start GDB with the exact ELF file that is currently flashed on the autopilot:

arm-none-eabi-gdb build/px4_fmu-v5_default/px4_fmu-v5_default.elf

Then, you have to select the Dronecode probe interface, on Linux this is e.g.:

target ext /dev/serial/by-id/usb-Black_Sphere_Technologies_Black_Magic_Probe_f9414d5_7DB85DAC-if00

Then you scan for the target:

monitor swdp_scan

And you should see something like:

Target voltage: 3.3V
Available Targets:
No. Att Driver
 1      STM32F76x M7

Note that for some autopilots it shows 0.0V but the subsequent steps work nevertheless.

You can now attach to that target:

attach 1

And now you should be connected.

To use the JLink debugger, you first need to install the JLink software (opens new window) containing the JLink GDB server.

The JLink installer should install the JLink GDB server to /usr/bin/. Once installed, you can start the server using:

JLinkGDBServer -if swd

It might then prompt you to update the JLink which is recommended, and then to specify which device it is communicating with. Check the docs of your autopilot for the specific device.

Once that's done, the GDB server should be start listening on port 2331, e.g. like so:

Checking target voltage...
Target voltage: 3.28 V
Listening on TCP/IP port 2331
Connecting to target...
Connected to target
Waiting for GDB connection...

You can now start GDB with the exact elf file that is currently flashed on the autopilot (in a separate terminal):

arm-none-eabi-gdb build/px4_fmu-v5_default/px4_fmu-v5_default.elf

And connect to the GDB server:

target remote :2331

And now you should be connected.

# GDB Quickstart

Once connected, you can use the usual GDB commands such as:

  • continue to continue program execution
  • run to start from the beginning
  • backtrace to see the backtrace
  • break somewhere.cpp:123 to set a breakpoint
  • delete somewhere.cpp:123 to remove it again
  • info locals to print local variables
  • info registers to print the registers

And much more, just use your favorite resource to learn more about GDB.


To avoid having to type all commands to connect in GDB each time, you can write them into ~/.gdbinit.