ESP32-C3: support audio file playback (SPI SD card and I2S audio out) (QEMU-297)

[dragonx]

Description

This PR adds just enough support to emulate audio playback from SD card on an emulated esp32-c3, specifically with MicroPython 1.26/1.27 (haven't tested 1.28 yet).

We add GDMA support for SPI2 read, and verified that mounting and reading a FAT16 SD card image works in MicroPython.

I2S0 output has been tested using the MicroPython I2S class, and has been tested with very limited scenarios: 16-bit, 44.1/48kHz, mono and stereo, that's all.

The emulated I2S0 device has an optional chardev sink for the PCM it drains from the I2S TX DMA stream. Attach any QEMU chardev with:

-chardev <backend>,id=i2s -global driver=esp32c3.i2s,property=chardev,value=i2s

Capture to a file for offline inspection:

-chardev file,id=i2s,path=/tmp/i2s_out.pcm -global driver=esp32c3.i2s,property=chardev,value=i2s

Or stream live over a (websocket-capable) socket, e.g.:

-chardev socket,id=i2s,host=127.0.0.1,port=5002,server=on,wait=off,websocket=on -global driver=esp32c3.i2s,property=chardev,value=i2s

The stream is raw interleaved signed 16-bit little-endian PCM at the configured sample rate / channel count. Buffer consumption is paced to ~real time from the I2S clock registers, so the capture runs at roughly the audio's natural duration.

Testing

Tested with micropython 1.26/1.27. A FAT SD Card image was created with multiple MP3 files, and mounted using:

            self.sd = SDCard(
                sck=Pin(self.SD_SCLK),
                mosi=Pin(self.SD_MOSI),
                miso=Pin(self.SD_MISO),
                cs=Pin(self.SD_CS),
            )
            vfs.mount(vfs.VfsFat(self.sd), "/sdcard")  # esp-adf seems to require the /sdcard name

I2S was initialized in MicroPython:

            i2s = I2S(
                0,
                sck=Pin(self.DAC_BCLK),
                ws=Pin(self.DAC_WCLK),
                sd=Pin(self.DAC_DIN),
                mode=I2S.TX,
                bits=16,
                format=I2S.MONO,
                rate=48000,
                ibuf=4096,
            )

MP3 files were decoded and played back using the esp-adf library.