system/cdcacm
^^^^^^^^^^^^^^^

  This very simple add-on allows the USB CDC/ACM serial device can be dynamically
  connected and disconnected from a host.  This add-on can only be used as
  an NSH built-in command.  If built-in, then two new NSH commands will be
  supported:

    1. sercon - Connect the CDC/ACM serial device
    2. serdis - Disconnect the CDC/ACM serial device

  Configuration prequisites (not complete):

    CONFIG_USBDEV=y                 : USB device support must be enabled
    CONFIG_CDCACM=y                 : The CDC/ACM driver must be built
    CONFIG_NSH_BUILTIN_APPS         : NSH built-in application support must be enabled

  Configuration options specific to this add-on:

    CONFIG_SYSTEM_CDCACM_DEVMINOR : The minor number of the CDC/ACM device.
                                    : i.e., the 'x' in /dev/ttyACMx

  If CONFIG_USBDEV_TRACE is enabled (or CONFIG_DEBUG and CONFIG_DEBUG_USB, or
  CONFIG_USBDEV_TRACE), then the add-on code will also initialize the USB trace
  output.  The amount of trace output can be controlled using:

  CONFIG_SYSTEM_CDCACM_TRACEINIT
    Show initialization events
  CONFIG_SYSTEM_CDCACM_TRACECLASS
    Show class driver events
  CONFIG_SYSTEM_CDCACM_TRACETRANSFERS
    Show data transfer events
  CONFIG_SYSTEM_CDCACM_TRACECONTROLLER
    Show controller events
  CONFIG_SYSTEM_CDCACM_TRACEINTERRUPTS
    Show interrupt-related events.

  Note:  This add-on is only enables or disable USB CDC/ACM via the NSH
  'sercon' and 'serdis' command.  It will enable and disable tracing per
  the settings before enabling and after disabling the CDC/ACM device. It
  will not, however, monitor buffered trace data in the interim.  If
  CONFIG_USBDEV_TRACE is defined (and the debug options are not), other
  application logic will need to monitor the buffered trace data.