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/*
* The MIT License (MIT)
*
* Copyright (c) 2026 Ha Thach (tinyusb.org)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*
*/
/* This example demonstrates a USB Printer + CDC composite device.
* Data received on the Printer interface is forwarded to the CDC serial port,
* and data received on the CDC serial port is forwarded back to the Printer interface.
*
* To test:
* 1. Flash the device
* 2. Open a serial terminal on the CDC port (e.g. /dev/ttyACM0)
* 3. Send data to the printer: echo "hello" > /dev/usb/lp0
* 4. The data appears on the CDC serial terminal
* 5. Type in the serial terminal to send data back through the printer TX
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "bsp/board_api.h"
#include "tusb.h"
#include "usb_descriptors.h"
// -------------------------------------------------------------------+
// Tasks
// -------------------------------------------------------------------+
// Forward data from Printer RX to CDC TX
static void printer_to_cdc_task(void) {
uint32_t avail = tud_printer_read_available();
if (avail == 0 || !tud_cdc_write_available()) {
return;
}
uint8_t buf[64];
uint32_t count = tud_printer_read(buf, TU_MIN(sizeof(buf), tud_cdc_write_available()));
if (count > 0) {
tud_cdc_write(buf, count);
tud_cdc_write_flush();
}
}
// Forward data from CDC RX to Printer TX
static void cdc_to_printer_task(void) {
uint32_t avail = tud_printer_write_available();
if (tud_cdc_available() == 0 || avail == 0) {
return;
}
uint8_t buf[64];
uint32_t count = tud_cdc_read(buf, TU_MIN(sizeof(buf), avail));
if (count > 0) {
tud_printer_write(buf, count);
tud_printer_write_flush();
}
}
int main(void) {
board_init();
// init device stack on configured roothub port
tusb_rhport_init_t dev_init = {.role = TUSB_ROLE_DEVICE, .speed = TUSB_SPEED_AUTO};
tusb_init(BOARD_TUD_RHPORT, &dev_init);
board_init_after_tusb();
while (1) {
tud_task(); // tinyusb device task
printer_to_cdc_task(); // forward printer data to CDC
cdc_to_printer_task(); // forward CDC data to printer
}
}
//--------------------------------------------------------------------+
// Printer callbacks
//--------------------------------------------------------------------+
void tud_printer_rx_cb(uint8_t itf) {
(void)itf;
}
// IEEE 1284 Device ID: first 2 bytes are big-endian total length (including the 2 length bytes).
// The rest is the Device ID string using standard abbreviated keys.
static const char printer_device_id[] =
"\x00\x34" // total length = 52 = 0x0034 (big-endian)
"MFG:TinyUSB;"
"MDL:Printer to CDC;"
"CMD:PS;"
"CLS:PRINTER;";
TU_VERIFY_STATIC(sizeof(printer_device_id) - 1 == 52, "device ID length mismatch");
uint8_t const *tud_printer_get_device_id_cb(uint8_t itf) {
(void)itf;
return (uint8_t const *)printer_device_id;
}
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