Hi Ryan Pearson ,
MSD is the USB bulk transfer, and HID is the Interrupt Endpoint transfer, so you can refer to the FRDM-K66 msd and HID code.
You can refer to the official SDK code for FRDM-K66, which can be downloaded from this link:
Welcome | MCUXpresso SDK Builder
Choose the FRDM-K66, then in the middleware, select the usb stack.

Then you can build the project, download the SDK code,and you can find the usb code in folder:
SDK_2.5.0_FRDM-K66F\boards\frdmk66f\usb_examples
Wish it helps you!
If you still have question about it, please kindly let me know.
Have a great day,
Kerry
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