Load the USB printer kernel module if not already loaded - Tinyusb

Printer to CDC

This example demonstrates a USB composite device with a Printer class interface and a CDC serial interface. Data flows bidirectionally between the two:

Data sent to the Printer (from host) is forwarded to the CDC serial port
Data sent to the CDC serial port (from host) is forwarded to the Printer IN endpoint

This is useful for debugging printer class communication or as a reference for implementing printer class devices.

USB Interfaces

Interface	Class	Description
0	CDC ACM	Virtual serial port
2	Printer	USB Printer (bidirectional, protocol 2)

How to Test

The device exposes two endpoints on the host:

/dev/ttyACM0 (CDC serial port)
/dev/usb/lp0 (USB printer)

Note: the actual device numbers may vary depending on your system.

Prerequisites (Linux):

bash

# Load the USB printer kernel module if not already loaded
sudo modprobe usblp

# Check devices exist
ls /dev/ttyACM* /dev/usb/lp*

Test Printer to CDC (host writes to printer, reads from CDC):

bash

# Terminal 1: read from CDC
cat /dev/ttyACM0

# Terminal 2: write to printer
echo "hello from printer" > /dev/usb/lp0
# "hello from printer" appears in Terminal 1

Test CDC to Printer (host writes to CDC, reads from printer):

bash

# Terminal 1: read from printer IN endpoint
cat /dev/usb/lp0

# Terminal 2: write to CDC
echo "hello from cdc" > /dev/ttyACM0
# "hello from cdc" appears in Terminal 1

Interactive bidirectional test:

bash

# Terminal 1: open CDC serial port
minicom -D /dev/ttyACM0

# Terminal 2: send to printer
echo "tinyusb print example" > /dev/usb/lp0
# Text appears in minicom. Type in minicom to send data back through printer TX.

IEEE 1284 Device ID

The device responds to GET_DEVICE_ID requests with:

MFG:TinyUSB;MDL:Printer to CDC;CMD:PS;CLS:PRINTER;

Verify with:

bash

cat /sys/class/usbmisc/lp0/device/ieee1284_id