DongLoRa Firmware

Embedded Rust firmware for DongLoRa boards. Exposes the LoRa radio over USB CDC-ACM using a COBS-framed binary protocol.

Building

just setup              # one-time toolchain install
just build heltec_v4    # build for a specific board
just flash heltec_v4    # build + flash
just check-all          # compile-check all boards
just clippy heltec_v4   # lint
just test               # host-side protocol unit tests

All commands are run from the firmware/ directory.

Supported Boards

Board	Feature	MCU	Radio	USB	Target
Heltec V3	heltec_v3	ESP32-S3	SX1262	Native CDC-ACM	xtensa-esp32s3-none-elf
Heltec V3 (UART)	heltec_v3_uart	ESP32-S3	SX1262	CP2102 bridge	xtensa-esp32s3-none-elf
Heltec V4	heltec_v4	ESP32-S3	SX1262	Native CDC-ACM	xtensa-esp32s3-none-elf
RAK WisBlock 4631	rak_wisblock_4631	nRF52840	SX1262	Native CDC-ACM	thumbv7em-none-eabihf
Wio Tracker L1	wio_tracker_l1	nRF52840	SX1262	Native CDC-ACM	thumbv7em-none-eabihf

Heltec V3 USB Note

The default heltec_v3 build uses native USB CDC-ACM, which requires a hardware modification to your board. Stock Heltec V3 boards route USB through a CP2102 bridge chip to UART — the ESP32-S3's native USB pins (GPIO19/GPIO20) are routed to header pins but not connected to the USB connector.

To enable native USB on a Heltec V3:

1. Solder 0-ohm (or 22-ohm) resistors at pads R29 (D+) and R3 (D-)
2. Disconnect the CP2102 from the USB connector's D+/D- lines (cut traces or remove the CP2102 bridge resistors)

After this mod, the board appears as /dev/ttyACM0 with the DongLoRa VID:PID (1209:5741), just like the V4 and nRF boards.

If you have a stock (unmodified) V3, use heltec_v3_uart instead:

just build heltec_v3_uart
just flash heltec_v3_uart

This builds firmware that communicates via the CP2102 bridge (appears as /dev/ttyUSB0).

Adding a Board

See src/board/PORTING.md.

Protocol

See PROTOCOL.md for the complete wire format specification.