CDC Dual Ports

Enumerates as a USB device with two independent CDC virtual serial ports.

What it does

Exposes two CDC virtual COM ports.
Echoes back any data received on either port to both ports: the first port echoes as lower case, the second as upper case.
Sends a UART state notification (toggles the DSR line) on each press of the on-board button.
Resets the board into the bootloader when the first port is opened at 1200 bps and then disconnected (touch-1200 trigger).
Blinks the on-board LED: 250 ms when unmounted, 1000 ms when mounted.

USB Descriptors

Interface	Class driver
0–1	CDC (virtual serial port 1)
2–3	CDC (virtual serial port 2)

Configuration

Notable tusb_config.h settings:

#define CFG_TUD_CDC               2   // two CDC ports
#define CFG_TUD_CDC_RX_BUFSIZE   (TUD_OPT_HIGH_SPEED ? 512 : 64)
#define CFG_TUD_CDC_TX_BUFSIZE   (TUD_OPT_HIGH_SPEED ? 512 : 64)

Building

CMake:

bash

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

Make:

bash

make BOARD=raspberry_pi_pico all

Try it

After flashing, two serial ports appear on the host (e.g. /dev/ttyACM0 and /dev/ttyACM1 on Linux). Open either one in a terminal and type: characters come back lower-cased on the first port and upper-cased on the second.