DFU Runtime

A minimal device that exposes a DFU runtime interface, advertising to the host that it can be switched into DFU (bootloader) mode.

What it does

Exposes a single DFU runtime interface alongside normal operation.
On a DFU_DETACH request, it does not actually reboot into a bootloader; instead it speeds up the LED blink as an indicator (this example is intentionally minimal).
Provides a BOS / Microsoft OS 2.0 descriptor so Windows binds the WinUSB driver.
LED blink rate indicates bus state (not mounted / mounted / suspended / DFU detach).

USB Descriptors

Interface	Class driver
0	DFU Runtime

Configuration

Notable tusb_config.h settings:

#define CFG_TUD_DFU_RUNTIME 1

Building

CMake:

bash

mkdir build && cd build
cmake -DBOARD=raspberry_pi_pico ..
cmake --build .

Make:

bash

make BOARD=raspberry_pi_pico all

Try it

List the device; it appears in Runtime mode:

bash

dfu-util -l

Request a switch to DFU mode:

bash

dfu-util -e

This sends a DETACH request. Since the example is minimal it does not enter a real bootloader; it instead changes the LED to a fast blink as confirmation.