oh my gosh! I worked and worked but didn't dig to deep on it...
I think GCLK5 could be used by Adafruit's QUAD flash chip? I also found that GCLK0 seems to be used by serial so I landed on GCLK1 as a good bet.
I forked your github and added support for the QUAD flash chip on the Adafruit Express Boards:
Medium quality output 8bit and up to 44.1khz if using QUAD SPI flash on the Adafruit M0 boards. Reduced quality ~22khz using an SD card.
It all sound fairly marginal at 8bit. Until we get 16bit DMA output going on the SAMD21, for good sound quality, I recommend going with a Teensy or a peripherial codec to do the heavy lifting.
This library plays WAV files stored on the SPI Flash Adafruit includes on their Express boards. This includes:
- Itsybits M0 Express (tested)
- Trinket M0 Express (have board will test)
- ItsyBitsy M4 Express
- Feather M0 Express