I finally have a driver that doesn't crash the OS. I also have a DAC plugged into the GPIOs. I also have a demo file of an MP3 of Take On Me converted to raw unsigned mono at 22.05 khz (I think, SOX's definition of raw is creative, it may still be PCM which I don't want). DDing the demo file to the device file puts a little under a minute of file into the buffer. The device then squeals for a fraction of a second and goes silent. I haven't figured out my error yet.