The TEENSY 3.1 is a small board with K20DX256-72MHz on it - see Teensy 3.1: New Features
Support for this platform has been added to the uTasker project - see USB-MSD boot loader µTasker Test Software and Demos
It is simulated as shown in the screen shot below. The simulator is available at: http://www.uTasker.com/freescale/Teensy_Simulator.zip Simply unzip the ZIP-file and execute the exe called "uTaskerV1-4_teensy_3_1".
By clicking on the pins of the Teensy module the K20 pins that are connected are visible (they toggle) - these pins then show their states and the peripheral functions that they can be used for (as well as the pin number on the physical device), which is quite useful when connecting up HW to the real board.
The simulation connects a UART to the PC's COM9. I use a COM port virtual loopback so that I can attach a terminal emulator to it. There is a command line menu there which allows various thing such as controlling ports (and the LED). In the simulator's menu, select "USB | Enumeration" to test USB enumeration (there is also output on the UART when this happend).