Rename the exising audiocore C module to _audiocore and create a new
Micropython wrapper module audiocore. This makes it easier to implement
async methods.
Add interrupt support to _audiocore that notifies core0 whenever data
has been consumed from the MP3 bitstream buffer.
Use this interrupt and an asyncio.ThreadSafeFlag to implement
audiocore.async_put which will play back the provided buffer, allowing
other async tasks to run while waiting for space in the bitstream
buffer.

@@ -27,0 +55,4 @@
+        uint32_t *buf;
+        if (multicore_fifo_rvalid()) {
+            cmd = multicore_fifo_pop_blocking();
+            switch (cmd) {

@@ -27,0 +87,4 @@
+                    i2s_play(samplerate);
+                    playing = true;
+                }
+                volume_adjust((int16_t *)buf, 2304, current_volume);

@@ -86,0 +89,4 @@
+// FLUSH - signals end of file and stop decoding when buffer empty - no arguments - return 0 when decoding is finished
+#define AUDIOCORE_CMD_FLUSH 0xdeadc0dd
+
+#define AUDIOCORE_MAX_VOLUME 0x8000u

@@ -80,0 +147,4 @@
+    i2s_context.cur_playing = 0;
+    memset(i2s_context.dma_buf, 0, sizeof(i2s_context.dma_buf[0][0]) * AUDIO_BUFS * I2S_DMA_BUF_SIZE);
+    i2s_max98357_program_init(audiocore_pio, i2s_context.pio_sm, i2s_context.pio_program_offset, i2s_context.out_pin,
+                              i2s_context.sideset_base, samplerate);

@@ -81,3 +157,4 @@
 {
     pio_sm_set_enabled(audiocore_pio, i2s_context.pio_sm, false);
     dma_channel_set_irq1_enabled(i2s_context.dma_ch, false);
+    dma_channel_abort(i2s_context.dma_ch);

@@ -63,2 +99,3 @@
     if (to_copy > 0) {
-        audiocore_audio_buffer_put(bufinfo.buf, to_copy);
+        audiocore_buffer_put(bufinfo.buf, to_copy);
+        __sev();

@@ -95,0 +143,4 @@
+    if (volume < 0 || volume > 255)
+        mp_raise_ValueError("volume out of range");
+    multicore_fifo_push_blocking(AUDIOCORE_CMD_SET_VOLUME);
+    multicore_fifo_push_blocking(AUDIOCORE_MAX_VOLUME * volume / 255);

@@ -0,0 +29,4 @@
+    }
+}
+
+static size_t __time_critical_func(mp3_get_continous_data)(unsigned char **readptr)