Make clock setup explicit instead of using the convoluted asf4 macro setup.
enable_clock_generator():
- Add GCLK_GENCTRL_OE to stick with the current setup.
- Handle divisor larger than 31 for generator 2
- Change the source argument so it can take the GCLK_GENCTRL_SRC_XXXX_Val
macros without casting to uint8_t.
This patch should not introduce any functional changes except keeping
GCLK_GENCTRL_OE enabled when the I2S clock is enabled.
This evolves the API from 2.x (and breaks it). Playback devices are now
separate from the samples themselves. This allows for greater playback
flexibility. Two sample sources are audioio.RawSample and audioio.WaveFile.
They can both be mono or stereo. They can be output to audioio.AudioOut or
audiobusio.I2SOut.
Internally, the dma tracking has changed from a TC counting block transfers
to an interrupt generated by the block event sent to the EVSYS. This reduces
the overhead of each DMA transfer so multiple can occure without using up TCs.
Fixes#652. Fixes#522. Huge progress on #263
