Firmware
A merged image starts at 0. An application on its own usually starts at 0x10000.
No image loaded.
ESP32 ESP Tool
Writes a merged image to an ESP32 over Web Serial, the way
esptool.py write_flash 0x0 image.bin does and with the same code underneath —
esptool-js, which resets the board into download mode, uploads its stub loader and verifies
what it wrote. Needs a Chromium-based browser over https:// or
http://localhost; nothing has to be done to the board first.
Device
No board connected.
Idle.
Notes
- The board is put into download mode for you. Starting it again afterwards is another matter: on a board whose USB-C goes straight to the SoC — a XIAO or a QT Py, as against a devkit with a bridge chip — nothing the host can send restarts it, so press RESET when the write is done. Either way the port goes with the restart.
- If it will not enter download mode by itself: hold BOOT, tap RESET, release BOOT — or, on a XIAO with no reset button, hold BOOT while plugging the cable in. Then connect and pick the port that appears.
- Flashing erases only what it writes. A merged image covers bootloader, partition table and application, so nothing of the old firmware is left behind.
- What was written is read back and compared by MD5 before the board is started.
- A board that stops appearing altogether after an interrupted write is not dead: its bootloader is rejecting the half-written application and restarting faster than the host can enumerate it. Hold BOOT, tap RESET, and plug into the machine rather than a hub. The ROM bootloader is in silicon and cannot be overwritten.
- A board running firmware that presents its own USB serial port — CircuitPython, for one — usually cannot be reset into download mode by the host at all, and needs its buttons.