usbserial USB Serial Hello World

Target configuration

This is another implementation of “Hello, World” but this one uses a USB serial driver. Configuration options can be used to simply the test. These options include:

  • CONFIG_EXAMPLES_USBSERIAL_INONLY – Only verify IN (device-to-host) data transfers. Default: both.

  • CONFIG_EXAMPLES_USBSERIAL_OUTONLY – Only verify OUT (host-to-device) data transfers. Default: both.

  • CONFIG_EXAMPLES_USBSERIAL_ONLYSMALL – Send only small, single packet messages. Default: Send large and small.

  • CONFIG_EXAMPLES_USBSERIAL_ONLYBIG – Send only large, multi-packet messages. Default: Send large and small.

If CONFIG_USBDEV_TRACE is enabled (or CONFIG_DEBUG_FEATURES and CONFIG_DEBUG_USB), then the example code will also manage the USB trace output. The amount of trace output can be controlled using:

  • CONFIG_EXAMPLES_USBSERIAL_TRACEINIT – Show initialization events.

  • CONFIG_EXAMPLES_USBSERIAL_TRACECLASS – Show class driver events.

  • CONFIG_EXAMPLES_USBSERIAL_TRACETRANSFERS – Show data transfer events.

  • CONFIG_EXAMPLES_USBSERIAL_TRACECONTROLLER – Show controller events.

  • CONFIG_EXAMPLES_USBSERIAL_TRACEINTERRUPTS – Show interrupt-related events.

Error results are always shown in the trace output.

Host-side test program

In additional to the target device-side example, there is also a host-side application in this directory. This host side application must be executed on a Linux host in order to perform the USBSERIAL test. The host application can be compiled under Linux (or Cygwin?) as follows:

cd examples/usbserial
make -f Makefile.host TOPDIR=<nuttx-directory>

Running the test

This will generate a small program called host. Usage:

  1. Build the examples/usbserial target program and start the target.

  2. Wait a bit, then do enter:

    dmesg

    At the end of the dmesg output, you should see the serial device was successfully idenfied and assigned to a tty device, probably /dev/ttyUSB0 or /dev/ttyACM0 (depending on the configured USB serial driver).

  3. Then start the host application:

    ./host [<tty-dev>]

    Where:

    • <tty-dev> is the USB TTY device to use. The default is /dev/ttyUSB0 (for the PL2303 emulation) or /dev/ttyACM0 (for the CDC/ACM serial device).

The host and target will exchange are variety of very small and very large serial messages.