Custom Firmware

There are two ways to change what runs on the 305ap:

• Startup files on the SD card: add commands or parameter defaults without rebuilding. Good for starting an extra driver or service.
• A custom build: change drivers, modules or code. Needed when something isn't in the standard firmware.

Try the SD card first. It survives firmware updates, and you can go back to stock by deleting a file.

Startup Files on the SD Card

PX4 checks the SD card for these files during boot:

File	Runs	Use for
/fs/microsd/etc/config.txt	Before most modules start, after parameter defaults	param set-default lines, early configuration
/fs/microsd/etc/extras.txt	At the end of startup	Starting extra drivers and services

The files are NSH scripts: one command per line, # for comments. Create the etc folder on the card if it doesn't exist.

Example extras.txt that starts ESC telemetry on the motor connector and an MS5611 barometer on the external SPI port:

# ESC serial telemetry on the motor connector (USART1, single-wire)
dshot telemetry -d /dev/ttyS0 -x

# MS5611 on external SPI, chip select 2
ms5611 -S -b 1 -c 2 start

You can write the file from the MAVLink Console, or put the SD card in a PC. Reboot to apply. Check the boot messages with dmesg to confirm the commands ran.

tip

Use param set-default (not param set) in config.txt. A default still lets you change the value from QGroundControl, and resetting parameters goes back to your default.

Custom Builds

Get the Source

The 305ap board target is in the avian automata PX4 fork:

git clone https://github.com/aaronfuller/PX4-Autopilot.git --recursive
cd PX4-Autopilot

See Building from Source for the toolchain setup.

Where to Make Changes

Change	File
Add or remove drivers and modules	boards/avianautomata/305ap/default.px4board (see px4board Config)
Board parameter defaults	boards/avianautomata/305ap/init/rc.board_defaults
Onboard sensor startup	boards/avianautomata/305ap/init/rc.board_sensors
Pin assignments, LEDs, ADC	boards/avianautomata/305ap/src/board_config.h and nuttx-config/include/board.h
NuttX (OS) options	boards/avianautomata/305ap/nuttx-config/nsh/defconfig

Prefer the board files over editing shared PX4 code. Board changes are easy to carry across PX4 updates; changes to shared drivers or modules conflict with upstream more often.

Build and Install

make avianautomata_305ap_default

Install build/avianautomata_305ap_default/avianautomata_305ap_default.px4 as described in Quickstart, Step 2, or upload directly:

make avianautomata_305ap_default upload

Commit your changes before building. The firmware records the git commit, and ver all then shows exactly which source a board is running.

Watch the Flash Budget

The default build is close to full (about 94% of flash). Adding a module may need another one removed. See px4board Config.

Going Back to Stock

• Delete config.txt and extras.txt from /fs/microsd/etc, and reboot.
• Install a release .px4 file to replace a custom build.
• To reset all parameters: param reset_all in the MAVLink Console, then reboot.