I need something to measure analog signals with at low frequencies (30-50Khz tops). The Teensy 3.1 happens to have an analog to digital converter capable of 500-800ksps at varying resolutions which should be sufficient for my needs.
The basic build structure (crt0, sysinit, etc) is expanded from
Karl Lunt's bare-metal
Teensy solution with some modifications. I used the V-USB driver and the
Teensyduino driver as partial templates for certain aspects of the USB driver,
but the code is all my own.