The libraries provide MTP interface to onboard microSD card in a Teensy 3.5/3.6 board via a connected host PC. To test it, please install Teensyduino version 1.39. Do the following steps: 1. Clone SdFat libraries from https://github.com/greiman/SdFat into your sketchbook libraries folder 2. Clone thie library https://github.com/greiman/MTP into your sketchbook libraries folder 3. Copy the files boards.txt into <Arduino's installation directory>/hardware/teensy/avr/ 4. Copy the files usb_desc.h into <Arduino's installation directory>/hardware/teensy/avr/cores/teensy3/ 5. Insert a FAT/FAT32 formatted microSD card into the on-board microSD card slot 6. Open the examples/MTP_blinky/MTP_blinky.ino program 7. Select USB Type "MTP Disk (Experimental)" 8. Compile and download the binary into Teensy 3.5/3.6 boards 9. Open serial monitor to see the trace See the history in https://forum.pjrc.com/threads/43050-MTP-Responder-Contribution?p=138772