14.1.1.2. Building the firmware

With the environment from Setting up the development environment in place, building a firmware image is two make commands plus a TARGET selection.

14.1.1.2.1. Compiling

First build mpy-cross, the host tool that compiles the frozen .py modules into bytecode (do this once, and again whenever you update MicroPython):

make -j$(nproc) -C lib/micropython/mpy-cross

Then build the firmware for a board, where <TARGET> is one of the names from the table below:

make -j$(nproc) TARGET=<TARGET>

-j$(nproc) builds in parallel across all CPU cores (on macOS use -j$(sysctl -n hw.ncpu)). TARGET is mandatory – make with no target aborts with “Invalid or no TARGET specified”.

A complete first build, end to end:

make sdk
make -j$(nproc) -C lib/micropython/mpy-cross
make -j$(nproc) TARGET=OPENMV4

14.1.1.2.1.1. Supported boards

TARGET values are the directory names under boards/. The cameras and their silicon:

Camera	TARGET	MCU	Port	Core
OpenMV Cam M4	OPENMV2	STM32F427	stm32	Cortex-M4
OpenMV Cam M7	OPENMV3	STM32F765	stm32	Cortex-M7
OpenMV Cam H7	OPENMV4	STM32H743	stm32	Cortex-M7
OpenMV Cam H7 Plus	OPENMV4P	STM32H743 + SDRAM	stm32	Cortex-M7
OpenMV Pure Thermal	OPENMVPT	STM32H743 + SDRAM	stm32	Cortex-M7
OpenMV Cam N6	OPENMV_N6	STM32N657	stm32	Cortex-M55
OpenMV Cam RT1062	OPENMV_RT1060	MIMXRT1062	mimxrt	Cortex-M7
OpenMV AE3	OPENMV_AE3	Alif Ensemble (dual M55)	alif	Cortex-M55
Arduino Portenta H7	ARDUINO_PORTENTA_H7	STM32H747	stm32	Cortex-M7
Arduino Giga	ARDUINO_GIGA	STM32H747	stm32	Cortex-M7
Arduino Nicla Vision	ARDUINO_NICLA_VISION	STM32H747	stm32	Cortex-M7
Arduino Nano 33 BLE Sense	ARDUINO_NANO_33_BLE_SENSE	nRF52840	nrf	Cortex-M4
Arduino Nano RP2040 Connect	ARDUINO_NANO_RP2040_CONNECT	RP2040	rp2	Cortex-M0+

Build the exact TARGET for your hardware – e.g. OPENMV4 for the OpenMV Cam H7, OPENMV4P for the H7 Plus, OPENMV_N6 for the N6.

14.1.1.2.1.2. Build output

Everything for a board lands in build/<TARGET>/bin/. For TARGET=OPENMV4 that is build/OPENMV4/bin/, containing:

File	What it is
firmware.bin	Firmware binary – flashed by OpenMV IDE Tools -> Load Custom Firmware and by dfu-util
firmware.elf	Firmware with debug symbols – the file you point the debugger at
bootloader.bin / .elf	The bootloader (only on boards with a bootloader enabled)
openmv.bin	Combined bootloader + firmware image
romfs<n>.img	Read-only ROM filesystem image flashed alongside the firmware

The Alif AE3 is dual-core, so it produces firmware_M55_HP.elf / firmware_M55_HP.bin (the high-performance core) and a separate firmware_M55_HE.elf / firmware_M55_HE.bin (the high-efficiency core) plus a table-of-contents (TOC) image that tells the boot ROM where each core’s image lives.

14.1.1.2.1.3. Cleaning and rebuilding

Builds are isolated per board under build/<TARGET>/. To wipe one board’s build:

make TARGET=<TARGET> clean

There is no distclean; clean always needs a TARGET. mpy-cross is shared across boards – if you update MicroPython, rebuild it too:

make -C lib/micropython/mpy-cross clean
make -j$(nproc) -C lib/micropython/mpy-cross

To report the flash/RAM usage of a build:

make TARGET=<TARGET> size

14.1.1.2.1.4. Building in Docker (no host toolchain)

If you would rather not install anything on the host (or you are on a platform without a native build), use the Docker path:

git clone --recursive https://github.com/openmv/openmv.git
cd openmv/docker
make TARGET=<TARGET>

Artifacts appear in openmv/docker/build/<TARGET>. For repeated builds there is an incremental dev path that mounts the repo at the same absolute path inside the container as on the host, so debugger source paths resolve without remapping:

make install-sdk
make build-firmware-dev TARGET=<TARGET>

Run make clean-dev when switching TARGET.

14.1.1.2.2. Build options

Build behavior is controlled by variables passed on the make command line, for example:

make -j$(nproc) TARGET=OPENMV4 DEBUG=1 V=1

The variables a firmware developer will use:

Variable	Default	Effect
TARGET	(required)	The board to build. Selects boards/<TARGET>/board_config.mk, which sets the MCU, core, memory map, USB IDs, and enabled modules.
DEBUG	0	DEBUG=1 compiles with -Og -ggdb3 (debug-optimized, full GDB debug info) and disables MicroPython ROM-text compression – this is the build you debug. DEBUG=0 compiles with -O2 -DNDEBUG (smaller, faster, asserts off) and is the release build.
V	0	V=1 prints every compiler/linker command instead of the short CC file.c summary. Use it to see exact flags or diagnose build issues.
DEBUG_PRINTF	0	DEBUG_PRINTF=1 defines OMV_DEBUG_PRINTF, enabling low-level debug printf output in the firmware (pair with SWO/RTT, see Debugging the firmware).
PROFILE_ENABLE	0	PROFILE_ENABLE=1 builds with function-call instrumentation (-finstrument-functions, -DOMV_PROFILER_ENABLE=1) so you can profile where time is spent. PROFILE_HASH=<N> sets the profiler hash-table size (power of two; default 256) and PROFILE_IRQ=1 also profiles code running in interrupt context.
STACK_PROTECTOR	0	STACK_PROTECTOR=1 adds -fstack-protector-all – stack canaries that trap stack-buffer overflows. Useful when chasing memory corruption.
DEBUGGER	JLINK	Which debugger the make debug / make deploy targets use. JLINK is the default; NONE disables the debug target.

Note

Many more variables exist (camera/sensor drivers, wireless stacks, ML backends, USB stack, secure boot, etc.), but those are set per-board in boards/<TARGET>/board_config.mk and are not normally overridden on the command line. Changing them is board customization, not a normal developer build – see docs/boards.md in the firmware repository.

For everyday work the only options you need are TARGET (always), DEBUG=1 (whenever you intend to debug, see Debugging the firmware), and occasionally V=1.