CDC + MSC

A composite USB device that exposes two interfaces at once:

CDC — a virtual serial port (/dev/ttyACMx, or a COM port on Windows) that echoes back everything it receives.
MSC — a small mass-storage disk that mounts as a removable drive.

This is the canonical TinyUSB example for a multi-interface (composite) device.

What it does

CDC: reads incoming data and echoes it straight back. Pressing the on-board button sends a serial-state (UART) notification to the host.
MSC: presents an 8 KB FAT12 RAM disk (16 × 512-byte blocks — the smallest size Windows will mount) labelled TinyUSB MSC, containing a single README.TXT. The disk lives in RAM, so changes are not persistent.
LED shows bus state: 250 ms blink = not mounted, 1000 ms = mounted, 2500 ms = suspended.

USB Descriptors

Interface	Class driver
0–1	CDC (virtual serial)
2	MSC (mass storage)

Configuration

Notable tusb_config.h settings:

#define CFG_TUD_CDC              1
#define CFG_TUD_MSC              1
#define CFG_TUD_CDC_RX_BUFSIZE   (TUD_OPT_HIGH_SPEED ? 512 : 64)
#define CFG_TUD_CDC_TX_BUFSIZE   (TUD_OPT_HIGH_SPEED ? 512 : 64)
#define CFG_TUD_MSC_EP_BUFSIZE   512

Building

CMake:

bash

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

Make:

bash

make BOARD=raspberry_pi_pico all

FreeRTOS variant

A FreeRTOS build is in examples/device/cdc_msc_freertos — identical CDC + MSC behavior, with the device, CDC, and LED-blink work split across FreeRTOS tasks.

Try it

Serial: open the CDC port (screen /dev/ttyACM0, PuTTY, …) and type — characters are echoed back.
Storage: a small TinyUSB MSC drive appears; open README.TXT to confirm it mounted.