USB CDC ACM Sample Application

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 samples/subsys/usb/cdc_acm in the Zephyr project tree.

Requirements

This project requires an USB device driver, which is available for Intel Quark* SE SoC based boards like Arduino/Genuino 101. For the Arduino 101 board you need a USB to 3.3V TTL serial cable. Connect it to UART1 as described in Connecting Serial Output section.

Building and Running

Arduino 101

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:

Using west:

west flash

Using CMake and ninja:

cmake -B build -GNinja -DBOARD=arduino_101 samples/subsys/usb/cdc_acm
ninja -C build flash

See Flashing the x86 Application Core section for details.

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:

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:

Wait for DTR

Open a serial port emulator, for example minicom and attach it to detected CDC ACM device:

minicom --device /dev/ttyACM1

The app should respond on serial output with:

DTR set, start test
Baudrate detected: 115200

And on ttyACM device, provided by zephyr USB device stack:

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 Arduino 101 to inform ModemManager to skip the CDC ACM device. For this example, it would look like this:

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.