The TWR-KW2x board's OpenSDA is programmed with PE Micro's OpenSDA firmware which enables MSD, debugging and CDC Serial port.
This firmware can be easily modified by putting the K20 part in bootloader mode and load another firmware to it with a simple drag and drop.
Follow these steps to modify the OpenSDA firmware on the TWR-KW2x board. Segger's OpenSDA v2.1 will be used as an example of the new OpenSDA firmware (Instead of the default PE Micro's)
1. Unplug the board
2. Insert a Jumper in J30 to put the device in Bootloader mode
3. Plug in the board (Mini-USB)
4. Device will be enumerated as a "Drive Disk" But now with a "Bootloader" label
5. Drag and Drop the Segger's JLink_OpenSDA_V2_1.bin firmware (https://segger.com/opensda.html) into the Bootloader unit
6. Unplug the board
7. Remove Jumper
8. Plug in the board (Mini-USB)
Now you should see the board being enumerated as "JLink CDC UART Port", allowing serial port communication.
You should also be able to debug your application using J-Link debugging interface through the OpenSDA interface, no need of external hardware.
Note1: Drivers can be found at Segger's website (https://segger.com/opensda.html)
Note2: Jumper has to be in place in J29 for debugging
Note3: IDE options must be set to use J-Link Driver