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third_party/tinyusb/examples/device/printer_to_cdc/README.md

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+#### 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 Descriptors
+
+| Interface | Class | Description |
+|-----------|-------|-------------|
+| 0 | CDC ACM | Virtual serial port |
+| 2 | Printer | USB Printer (bidirectional, protocol 2) |
+
+#### Configuration
+
+Notable `tusb_config.h` settings:
+
+```c
+#define CFG_TUD_CDC                1
+#define CFG_TUD_PRINTER            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_PRINTER_RX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
+#define CFG_TUD_PRINTER_TX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
+```
+
+#### 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
+```