micro:bit v2 Flasher

Build your program and flash it to a BBC micro:bit v2 over WebUSB, from inside VS Code — including a GitHub Codespace, which has no USB port of its own.

One key does the whole job: Ctrl+F5, the same key that builds and flashes on your own machine (Ctrl+Shift+B only builds), or the Flash micro:bit button in the status bar. It runs the workspace Build task, then flashes build/main.hex. The first time, the browser asks which USB device to use — choose the micro:bit. Then the micro:bit › Serial view opens in the bottom panel: your program's output over the same USB connection, an input field to send it a line (Enter sends CR LF), Clear, and header buttons to connect, flash and disconnect. The micro:bit output channel carries the extension's own log.

Made for the Ada micro:bit course template; it flashes any Intel HEX at build/main.hex, whatever produced it.

Debugging with breakpoints

In a Codespace, F5 works through this extension as well. arm-eabi-gdb runs in the Codespace, where the program's symbols are; the companion extension there opens a port for it and forwards every gdb packet to this extension, which answers over the board's USB connection: halting, stepping, registers, memory, six hardware breakpoints, and gdb's load, which flashes. The first time, F5 asks which USB device to use, just as Ctrl+F5 does; after that the board is remembered. The micro:bit: (internal) gdb … commands are the companion's end of that conversation, not for people.

Where it runs

This is a web extension: VS Code runs it in the browser, on your own machine, where the board is plugged in — not in the Codespace, which cannot see your USB ports. Install it from the Extensions view of a Codespace opened in the browser (or vscode.dev / github.dev); if VS Code offers a choice, pick Install in Browser. Installed into the Codespace it can never start.

It needs a Chromium browser — Chrome, Edge or Opera. Safari and Firefox have no WebUSB. Desktop VS Code has no USB picker, so there the flash runs the workspace's Build & Flash task instead, which flashes with pyocd (the course template's python3 mb.py flash), and the Serial view's boards and serial come from the micro:bit Companion extension, which runs python3 mb.py boards next to the board.

The Serial view

The view lists every micro:bit it can see, tells a v2 from a v1 by the board id in its USB serial number (a v1 is listed but cannot be chosen), and follows your pick: in the browser that is the authorised device it connects to, on your own machine the port the companion reads and the board pyocd flashes (build/board.txt). Plugging a board in or out updates the list, and an unplugged board that was connected is let go of. Show serial is not cosmetic: unticked, the port is not read, in the browser because the library polls DAPLink only while something listens, on your machine because the companion closes the port.

Commands

Source

extension/ in the template repository. python3 mb.py extension assembles this folder, bundling @microbit/microbit-connection into it; it is published with vsce by the repository's workflow.