Audio System + Drivers (#562)

Drivers/audio-codec-module/README.md

@@ -0,0 +1,19 @@
+# Audio codec module
+
+Defines `AUDIO_CODEC_TYPE` and the codec-agnostic `AudioCodecApi` (open/close/
+read/write/volume/mute/native-rate/native-channels/capabilities) that every
+audio codec driver in this repo implements (ES8311, ES8388, ES7210, AW88298,
+the dummy I2S amps, the PDM mic). This is intentionally low-level: no
+resampling or mixing, one codec device per chip. Most app code should go
+through `audio_stream` (see `Drivers/audio-stream-module`) instead of talking
+to a codec device directly.
+
+Also provides `audio_codec_adapters.h`: glue that lets a codec driver build an
+`esp_codec_dev` control/data/GPIO interface (`audio_codec_ctrl_if_t` /
+`audio_codec_data_if_t` / `audio_codec_gpio_if_t`) directly from Tactility's
+own I2C controller, I2S controller, and GPIO pin devices, so a codec driver
+only ever needs `device_get_parent()`/`device_find_by_name()` plus a handful
+of devicetree properties -- it never touches the platform I2C/I2S/GPIO APIs
+directly.
+
+License: [Apache v2.0](LICENSE-Apache-2.0.md)