MultiCDC

This is a simple RP2040-based 6-channel USB to UART converter.

This is my first project using the Zephyr RTOS, so there might be lots of mistakes. However, it seems to work.

Operation

The device creates 7 /dev/ttyACM* devices when connected to a linux host. The first 6 are linked to hardware UARTs, and /dev/ttyACM6 is used for logging and shell.

The RP2040 only has 2 hardware UARTs. The other 4 channels use the PIOs.

Unfortunately, the pico-uart-pio driver doesn't allow changing the baud rate at runtime. For this reason, baud rates (current-speed) for those channels need to be set in the device tree (app.overlay).

Pin map (most of these can be changed arbitrarily):

pin	function
P0	Tx0
P1	Rx0
P2	Tx1
P3	Rx1
P4	Tx2
P5	Rx2
P6	Tx3
P7	Rx3
P8	Tx4
P9	Rx4
P10	Tx5
P11	Rx5

Build

. ~/zephyrproject/.venv/bin/activate
. ~/zephyrproject/zephyr/zephyr-env.sh
west build

# enter bootloader: press BOOT button, press & release RESET, release BOOT
west flash

Udev rules

sudo tee /etc/udev/rules.d/99-multicdc.rules > /dev/null << "EOF"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="00", SYMLINK+="tty-mcdc0ch0"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="02", SYMLINK+="tty-mcdc0ch1"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="04", SYMLINK+="tty-mcdc0ch2"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="06", SYMLINK+="tty-mcdc0ch3"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="08", SYMLINK+="tty-mcdc0ch4"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="0a", SYMLINK+="tty-mcdc0ch5"
SUBSYSTEM=="tty", ENV{ID_VENDOR_ID}=="2fe3", ENV{ID_MODEL_ID}=="6cdc", ENV{ID_USB_INTERFACE_NUM}=="0c", SYMLINK+="tty-mcdc0shell"
EOF

sudo udevadm control --reload-rules
sudo udevadm trigger