Audio System + Drivers (#562)

Drivers/es7210-module/README.md

@@ -0,0 +1,18 @@
+# ES7210 microphone ADC
+
+A driver for the `ES7210` 4-channel microphone ADC by Everest Semiconductor,
+wired as an input-only `AUDIO_CODEC_TYPE` device. The I2C bus is the device's
+parent; the I2S controller carrying the (4-slot TDM) audio data is referenced by
+name.
+
+Always configures the hardware for the full 4-slot TDM frame regardless of how
+many mics are actually wired (`mic-mask`), then demuxes down to just the active
+mic slots in software -- `es7210_set_fs()` silently halves the configured bit
+depth when asked for 2 or fewer TDM channels, which corrupts audio if the mic
+count is passed straight through.
+
+Wraps Espressif's `esp_codec_dev` ES7210 implementation.
+
+See https://www.everest-semi.com/pdf/ES7210%20PB.pdf
+
+License: [Apache v2.0](LICENSE-Apache-2.0.md)