Use PDM audio on esp32-c3-lyra board

The I2S data pin is hooked up directly to the amplifier on this board,
so while it does generate sound, it sounds terrible since it's not
actually handling the data signal.  The sample implementation in the
esp-adf uses the I2S hardware with PDM encoding to drive the amp.

https://github.com/espressif/esp-adf/blob/ad4ac707c5dffb450dbabfdcaa7443165ee4e852/examples/player/pipeline_spiffs_mp3/main/play_spiffs_mp3_example.c#L76

This change hardcodes the PDM implementation for this board.

Author: gychang

ports/espressif/boards/espressif_esp32c3_lyra_v2/mpconfigboard.mk

@@ -10,5 +10,7 @@ CIRCUITPY_ESP_FLASH_SIZE = 4MB
 CIRCUITPY_ESP_USB_SERIAL_JTAG = 0
 
 ESPRESSIF_ESP32C3_LYRA_STATUS_LED_HOLD = 1
+ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT = 1
 
 CFLAGS += -DESPRESSIF_ESP32C3_LYRA_STATUS_LED_HOLD=$(ESPRESSIF_ESP32C3_LYRA_STATUS_LED_HOLD)
+CFLAGS += -DESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT=$(ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT)

ports/espressif/common-hal/audiobusio/I2SOut.c

@@ -25,12 +25,29 @@
 
 #include "driver/i2s_std.h"
 
+#if ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT
+#include "driver/i2s_pdm.h"
+#endif
+
 // Caller validates that pins are free.
 void common_hal_audiobusio_i2sout_construct(audiobusio_i2sout_obj_t *self,
     const mcu_pin_obj_t *bit_clock, const mcu_pin_obj_t *word_select,
     const mcu_pin_obj_t *data, const mcu_pin_obj_t *main_clock, bool left_justified) {
     port_i2s_allocate_init(&self->i2s, left_justified);
 
+    #if ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT
+    i2s_pdm_tx_config_t pdm_tx_cfg = {
+        .clk_cfg = I2S_PDM_TX_CLK_DEFAULT_CONFIG(16000),
+        .slot_cfg = I2S_PDM_TX_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO),
+        .gpio_cfg = {
+            .dout = data->number,
+            .invert_flags = {
+                .clk_inv = false,
+            },
+        },
+    };
+    CHECK_ESP_RESULT(i2s_channel_init_pdm_tx_mode(self->i2s.handle, &pdm_tx_cfg));
+    #else
     i2s_std_config_t i2s_config = {
         .clk_cfg = I2S_STD_CLK_DEFAULT_CONFIG(48000),
         .slot_cfg = I2S_STD_PHILIPS_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_STEREO),
@@ -43,6 +60,7 @@ void common_hal_audiobusio_i2sout_construct(audiobusio_i2sout_obj_t *self,
         }
     };
     CHECK_ESP_RESULT(i2s_channel_init_std_mode(self->i2s.handle, &i2s_config));
+    #endif
     self->bit_clock = bit_clock;
     self->word_select = word_select;
     self->mclk = main_clock;

ports/espressif/common-hal/audiobusio/__init__.c

@@ -19,10 +19,18 @@
 #define I2S_DMA_BUFFER_MAX_SIZE     4092
 // The number of DMA buffers to allocate
 #define CIRCUITPY_BUFFER_COUNT (3)
+
+#if ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT
+// The maximum DMA buffer size in frames (at mono 16-bit)
+#define CIRCUITPY_BUFFER_SIZE (I2S_DMA_BUFFER_MAX_SIZE / 8)
+// The number of output channels is fixed at 1
+#define CIRCUITPY_OUTPUT_SLOTS (1)
+#else
 // The maximum DMA buffer size in frames (at stereo 16-bit)
 #define CIRCUITPY_BUFFER_SIZE (I2S_DMA_BUFFER_MAX_SIZE / 4)
 // The number of output channels is fixed at 2
 #define CIRCUITPY_OUTPUT_SLOTS (2)
+#endif
 
 static void i2s_fill_buffer(i2s_t *self) {
     if (self->next_buffer_size == 0) {
@@ -31,7 +39,7 @@ static void i2s_fill_buffer(i2s_t *self) {
     }
     int16_t *output_buffer = (int16_t *)self->next_buffer;
     size_t output_buffer_size = self->next_buffer_size;
-    const size_t bytes_per_output_frame = 4;
+    const size_t bytes_per_output_frame = CIRCUITPY_OUTPUT_SLOTS * 2;
     size_t bytes_per_input_frame = self->channel_count * self->bytes_per_sample;
     if (!self->playing || self->paused || !self->sample || self->stopping) {
         memset(output_buffer, 0, self->next_buffer_size);
@@ -62,7 +70,8 @@ static void i2s_fill_buffer(i2s_t *self) {
         size_t sample_bytecount = self->sample_end - self->sample_data;
         // The framecount is the minimum of space left in the output buffer or left in the incoming sample.
         size_t framecount = MIN(output_buffer_size / bytes_per_output_frame, sample_bytecount / bytes_per_input_frame);
-        if (self->samples_signed && self->channel_count == 2) {
+
+        if (self->samples_signed && self->channel_count == CIRCUITPY_OUTPUT_SLOTS) {
             if (self->bytes_per_sample == 2) {
                 memcpy(output_buffer, self->sample_data, framecount * bytes_per_output_frame);
             } else {
@@ -165,8 +174,16 @@ void port_i2s_play(i2s_t *self, mp_obj_t sample, bool loop) {
     audiosample_reset_buffer(self->sample, false, 0);
 
     uint32_t sample_rate = audiosample_get_sample_rate(sample);
+
+    #if ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT
+    i2s_pdm_tx_clk_config_t clk_config = I2S_PDM_TX_CLK_DEFAULT_CONFIG(sample_rate);
+    CHECK_ESP_RESULT(i2s_channel_reconfig_pdm_tx_clock(self->handle, &clk_config));
+    size_t frame_size = sizeof(uint16_t);
+    #else
     i2s_std_clk_config_t clk_config = I2S_STD_CLK_DEFAULT_CONFIG(sample_rate);
     CHECK_ESP_RESULT(i2s_channel_reconfig_std_clock(self->handle, &clk_config));
+    size_t frame_size = sizeof(uint32_t);
+    #endif
 
     // preload the data
     self->playing = true;
@@ -183,12 +200,12 @@ void port_i2s_play(i2s_t *self, mp_obj_t sample, bool loop) {
         self->next_buffer = &starting_frame;
         self->next_buffer_size = sizeof(starting_frame);
         i2s_fill_buffer(self);
-        i2s_channel_preload_data(self->handle, &starting_frame, sizeof(uint32_t), &bytes_loaded);
+        i2s_channel_preload_data(self->handle, &starting_frame, frame_size, &bytes_loaded);
         preloaded += bytes_loaded;
     }
 
     // enable the channel
-    i2s_channel_enable(self->handle);
+    CHECK_ESP_RESULT(i2s_channel_enable(self->handle));
 
     // The IDF will call us back when there is a free DMA buffer.
 }

ports/espressif/common-hal/audiobusio/__init__.h

@@ -12,6 +12,10 @@
 
 #include "driver/i2s_std.h"
 
+#if ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT
+#include "driver/i2s_pdm.h"
+#endif
+
 typedef struct {
     mp_obj_t *sample;
     bool left_justified;

ports/espressif/mpconfigport.mk

@@ -349,3 +349,6 @@ USB_NUM_IN_ENDPOINTS = 5
 
 # Usually lots of flash space available
 CIRCUITPY_MESSAGE_COMPRESSION_LEVEL ?= 1
+
+ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT ?= 0
+CFLAGS += -DESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT=$(ESPRESSIF_ESP32C3_LYRA_AUDIOBUSIO_PDMOUT)