GDB OCD loader

Automatically start gdb-server from within GDB

When developing for ARM Cortex-M microcontrollers, it's often needed to restart the GDB server. This is a helper to manage the gdb server instances from within gdb.

Setup your .gdbinit with the probes available, then simply use command connect to start the gdb server, and connect to it.

Command reload will the recompile your application, reload the target and restart the gdb server.

Supported gdb-servers

Multiple gdb-servers are supported:

• pyOCD - generic interface which is RTOS aware. Originally developed for.
• openocd - currently preferred interface. RTOS aware too. Supports most probes.
• jlink - Not RTOS-aware, but commonly used. If application doesn't use RTOS threads, it may be a good choice.
• st-link - Used for stm32 targets using the st-link. However, also supported by openocd

Install

Install a version of gdb that supports python. gdb-multiarch is recommended, but arm-none-eabi-gdb-py should work too.

On Ubuntu 22.04:

apt install gdb-multiarch

Then clone this repo in a location of choice, for example in the home directory:

cd ~
git clone https://github.com/pengi/gdb_ocd_loader.git

Use the gdbinit_template.gdb in this repo as template for your ~/.gdbinit to load gdb_ocd_loader.

Configuration

Follow instructions in gdbinit_template.gdb

The probes available are:

OpenOCD

alias my_probe = python probe_setup(probe_openocd, "interface", "target", "command")

"command" is optional, and will add commands to the openocd script. Useful for selecting a sepcific interface, for example jlink serial 123456789.

"command" can be an array to specify multiple commands.

pyOCD

alias my_probe = python probe_setup(probe_pyocd, "target", "id", "pack file")

st-link

alias my_probe = python probe_setup(probe_stlink, "target", "id")

jlink

alias my_probe = python probe_setup(probe_pyocd, "target", "id")

gdb usage

To connect to a probe, run the command specified as alias, in this example nrf, followed by connect:

(gdb) nrf
(gdb) connect

openocd (or the gdb server specified) will start and auto connect.

Some gdb-servers (in particular pyocd), needs the elf file when starting, to identify RTOS threads. Therefore, restart is recommended when reloading. connect will automatically disconnect previous connection before reconneting.

(gdb) load
(gdb) connect

Resetting the device, it is usually expected that the device is halted after reset. The command to reset in pyocd is monitor reset halt, which is added as an alias above:

(gdb) res

When developing, the target .elf file is usually in the same directory, and make myfile.elf rebuilds it, then there is a shortcut:

(gdb) reload

This will disconnect the probe, rebuild the software, flash it and reconnect.

OS aware debugging

If using an RTOS aware gdb-server, for example openocd or pyocd, it is possible to list RTOS tasks and inspect RTOS tasks:

(gdb) info threads
...
(gdb) thread apply all bt
...

arm-gdb and freertos-gdb

Two useful tools to first inspect the ARM System Control Block and NVIC registers

(gdb) arm scb
...
(gdb) arm nvic

More information at: https://pypi.org/project/arm-gdb/

And

(gdb) freertos queue
...

More information at: https://pypi.org/project/freertos-gdb/