14.1.1.3.5.2. OpenMV AE3: dfu-util¶

The OpenMV AE3 uses the openmv_dfu bootloader (application VID:PID 37C5:16E3, DFU VID:PID 37C5:96E3), but it is a dual-core device: an Alif Ensemble with a high-performance (HP) and a high-efficiency (HE) Cortex-M55 core. To enter the bootloader, just plug the camera in: it listens briefly at power-up, and -w makes dfu-util wait for it to appear. Each core runs its own firmware image and has its own read-only ROMFS, so a full flash is four images:

Core	Firmware command	ROMFS command
M55-HP	`-a 1 -D firmware_M55_HP.bin`	`-a 6 -D romfs0.img`
M55-HE	`-a 2 -D firmware_M55_HE.bin`	`-a 3 -D romfs1.img`

A full flash writes the four images, with --reset only on the final transfer:

dfu-util -w -d ,37C5:96E3 -a 1 -D firmware_M55_HP.bin
dfu-util -w -d ,37C5:96E3 -a 2 -D firmware_M55_HE.bin
dfu-util -w -d ,37C5:96E3 -a 3 -D romfs1.img
dfu-util -w -d ,37C5:96E3 -a 6 --reset -D romfs0.img

To replace just one core’s firmware, flash only that core’s alt (-a 1 for HP, -a 2 for HE); to replace one core’s ROMFS, flash that core’s ROMFS alt (-a 6 for HP / romfs0, -a 3 for HE / romfs1).

14.1.1.3.5.2.1. Initializing the Everspin MRAM¶

Special builds of the OpenMV AE3 replace the standard external flash – which holds the internal FAT filesystem and the HP core’s ROMFS – with an Everspin MRAM chip. This section applies to those builds only. An Everspin part that has never been initialized, or whose configuration registers have been corrupted, does not respond to writes, so DFU transfers to those alts fail until the chip is re-initialized.

The bootloader exposes this as one more DFU alt: downloading a key file to -a 7 triggers the initialization sequence (a JESD reset, configuration-register initialization, lock removal, and two full chip-erase passes). The download itself stores nothing – the partition checks that the file starts with the expected 16-byte key and runs the sequence, at most once per bootloader session.

Generate the key file with tools/flash_recovery_key.py from the firmware repository (it writes a 4 KB key.bin), then download it:

python tools/flash_recovery_key.py
dfu-util -w -d ,37C5:96E3 -a 7 -D key.bin

The chip is blank afterwards: re-flash the HP core’s ROMFS (-a 6 -D romfs0.img), and the internal FAT filesystem reformats itself on the next boot.