.. zephyr:code-sample:: usb-cdc-acm
:name: USB CDC-ACM
:relevant-api: usbd_api _usb_device_core_api uart_interface
Use USB CDC-ACM driver to implement a serial port echo.
Overview
********
This sample app demonstrates use of a USB Communication Device Class (CDC)
Abstract Control Model (ACM) driver provided by the Zephyr project.
Received data from the serial port is echoed back to the same port
provided by this driver.
This sample can be found under :zephyr_file:`samples/subsys/usb/cdc_acm` in the
Zephyr project tree.
Requirements
************
This project requires an USB device driver, which is available for multiple
boards supported in Zephyr.
Building and Running
********************
Reel Board
===========
To see the console output of the app, open a serial port emulator and
attach it to the USB to TTL Serial cable. Build and flash the project:
.. zephyr-app-commands::
:zephyr-app: samples/subsys/usb/cdc_acm
:board: reel_board
:goals: flash
:compact:
Running
=======
Plug the board into a host device, for example, a PC running Linux.
The board will be detected as shown by the Linux dmesg command:
.. code-block:: console
usb 9-1: new full-speed USB device number 112 using uhci_hcd
usb 9-1: New USB device found, idVendor=8086, idProduct=f8a1
usb 9-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 9-1: Product: CDC-ACM
usb 9-1: Manufacturer: Intel
usb 9-1: SerialNumber: 00.01
cdc_acm 9-1:1.0: ttyACM1: USB ACM device
The app prints on serial output (UART1), used for the console:
.. code-block:: console
Wait for DTR
Open a serial port emulator, for example minicom
and attach it to detected CDC ACM device:
.. code-block:: console
minicom --device /dev/ttyACM1
The app should respond on serial output with:
.. code-block:: console
DTR set, start test
Baudrate detected: 115200
And on ttyACM device, provided by zephyr USB device stack:
.. code-block:: console
Send characters to the UART device
Characters read:
The characters entered in serial port emulator will be echoed back.
Troubleshooting
===============
If the ModemManager runs on your operating system, it will try
to access the CDC ACM device and maybe you can see several characters
including "AT" on the terminal attached to the CDC ACM device.
You can add or extend the udev rule for your board to inform
ModemManager to skip the CDC ACM device.
For this example, it would look like this:
.. code-block:: none
ATTRS{idVendor}=="8086" ATTRS{idProduct}=="f8a1", ENV{ID_MM_DEVICE_IGNORE}="1"
You can use
``/lib/udev/rules.d/77-mm-usb-device-blacklist.rules`` as reference.
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