FMU Debugging

On Skynode S the FMU is tightly integrated with AOS including access to the serial console of PX4 and debug access for GDB.

PX4 shell access via SSH

The PX4 shell (NSH) is connected to the Linux companion via UART and can be accessed from inside AOS with picocom:

picocom -b 57600 /dev/ttymxc1

This allows you to access the PX4 shell even when the Mavshell is not working.

nsh> reboot
[boot] Rev 0x15 : Ver 0x12 V6S015
[boot] Fault Log info File No 4 Length 3177 flags:0x01 state:1
[boot] Fault Log is Armed
HW arch: AUTERION_FMU_V6S
HW type: V6S
HW FMUM ID: 0x015
HW BASE ID: 0x012

You can exit picocom with Ctrl-a-x.

GDB access via SSH

Debugging via GDB halts the FMU, which can lead to unpredictable behavior. Only use this method to debug the FMU without any motors attached! NEVER DEBUG IN FLIGHT!

The SWD lines of the FMU are also connected to the Linux companion and can be bit-banged via OpenOCD. This connection can be exposed as a GDB Server on the USB-C ethernet interface:

openocd -f board/px4_fmu-v6s.cfg \
    -c "bindto 10.41.1.1" -c init

Adapt the IP address for other connected links to debug over radios.

Connecting GDB to this server requires setting the correct IP address too:

arm-none-eabi-gdb auterion_fmu-v6s_default.elf \
	-ex "target extended-remote 10.41.1.1:3333"

For better GDB integration with PX4, we recommend using the Auterion Embedded Debug Tools:

python3 -m emdbg.bench.fmu --remote 10.41.1.1:3333 \
    --target auterion_fmu-v6s_default