Proposal: Optional interrupt callback for the I2S DMA IRQ handler

[c3hodgins]

I've forked the repository in order to make modifications to the audio_i2s interface, in order to allow a callback function to be registered to the DMA IRQ handler in the I2S PIO interface. The added void function pointer for the callback and the callback registration function do not affect audio playback if no callback is registered.

Use case:

• Allows application level callback function definition for processing that is paced with the audio sample generation and buffer writing.
• Provides clean integration to extend the capability of the current I2S implementation without interfering with rest of interface.

Application:

• Sampling a software controlled oscillator.
• Generating waveform envelopes and filtering

Question for maintainers:

• Is this something you would consider upstream, or should it remain a forked extension for DSP use cases?