For a project I want to use the Teensy 3.1 board (see “Hacking the Teensy V3.1 for SWD Debugging“) in USB CDC mode: that way the Teensy board can connect to the host and exchange data or attach a console to the Teensy board: that way I can connect the Teensy over USB to the host use the USB as communication interface:

Teensy with Octo WS2811 Board

I’m using the Teensy in a ‘non-standard’ way: I’m debugging it with a SWD debug probe so I have complete control over the hardware. See “Hacking the Teensy V3.1 for SWD Debugging“:

Debugging Teensy with P&E Multilink SWD Debug Probe

I have published a KDS V2.0.0 project on GitHub here:
https://github.com/ErichStyger/mcuoneclipse/tree/master/Examples/KDS/Teensy_3.1/Teensy3.1_CDC

Teensy 3.1 USB CDC Project

If you want to create such a project yourself (e.g. with Kinetis Design Studio, using V2.0.0), here are the steps:

1. Make sure you have the latest components from SourceForge (see “McuOnEclipse Releases on SourceForge“)
2. Create a new project (File > New > Kinetis Design Project) for the MK20DX256xxx7 72 MHz) microcontroller:
   

   MK20DX256

3. Configure the CPU clocks to use the 16 MHz external crystal and PEE mode:
   

   PEE Mode

4. MCG settings are for PEE and 96 MHzPLL output clock:
   

   MCG Settings

5. Configure the core clocks. Important part is to use the PLL clock selection and that it shows 96 MHz at the bottom:
   

   System Clocks

6. Add the FSL_USB_Stack component to the project:
   

   FSL_USB_Stack Component

7. Use Init_USB_OTG_VAR0 for initialization and set device class to CDC Device:
   

   FSL_USB_Stack Configuration

8. In the Init component, enable the clock and configure it for 48 MHz using thePLL/FLL clock:
   

   USB Initialization

9. Specify the CPU in the CDC device component:
   

   CPU in CDC Device

10. Configure the Rx andTx ring buffers: Use an appropriate buffer size for both (e.g. 64 bytes). Do this both for Rx andTx:
    

    Ring Buffers

    

    Ring Buffer Size

With this, everything is configured. Generate Code with Processor Expert, and you can add your application code. The following is a bare metal example which waits until the USB device has been enumerated, then it communicates over USB CDC with the host:

static uint8_t cdc_buffer[USB1_DATA_BUFF_SIZE];
static uint8_t in_buffer[USB1_DATA_BUFF_SIZE];

static void CDC_Run(void) {
  int i, cnt = 0;
  uint32_t val = 0;
  unsigned char buf[16];

  for(;;) {
    while(CDC1_App_Task(cdc_buffer, sizeof(cdc_buffer))==ERR_BUSOFF) {
      /* device not enumerated */
      LED1_Neg();
      WAIT1_Waitms(10);
    }
    if (CDC1_GetCharsInRxBuf()!=0) {
      i = 0;
      while(   i<sizeof(in_buffer)-1
            && CDC1_GetChar(&in_buffer[i])==ERR_OK
           )
      {
        i++;
      }
      in_buffer[i] = '\0';
      (void)CDC1_SendString((unsigned char*)"echo: ");
      (void)CDC1_SendString(in_buffer);
      UTIL1_strcpy(buf, sizeof(buf), (unsigned char*)"val: ");
      UTIL1_strcatNum32u(buf, sizeof(buf), val);
      UTIL1_strcat(buf, sizeof(buf), (unsigned char*)"\r\n");
      (void)CDC1_SendString(buf);
      val++;
      LED1_Neg();
    } else {
      WAIT1_Waitms(10);
      cnt++;
      if ((cnt%128)==0) {
        LED1_Neg();
      }
      if ((cnt%1024)==0) { /* from time to time, write some text */
        (void)CDC1_SendString((unsigned char*)"Type some text and it will echo.\r\n");
        CDC1_SendBlock((unsigned char*)"hello?\r\n", sizeof("hello?\r\n")-1);
      }
    }
  }
}

Happy Teensing 🙂