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前言
esp32-ADF音频框架，Demo看了好几次，也只知道个大概。音频涉及的东西太多了，入门就先熟悉这个框架。 官方文档：https://docs.espressif.com/projects/esp-adf/en/latest/api-reference/index.html
Elements of the Audio Development Framework  框架中包含流、编解码器、音频处理相关的方法和概念。
Sample Organization of Elements in Audio Pipeline 将MP3解码器和I2S流两个元素添加进管道，解码器的输入是MP3文件数据流，I2S流将解码后的音频数据输出到片外，各应用程序之间通过事件接口通信。 
1. 代码分析
static const char *TAG = "PLAY_MP3_FLASH";
/*
To embed it in the app binary, the mp3 file is named
in the component.mk COMPONENT_EMBED_TXTFILES variable.
*/
extern const uint8_t adf_music_mp3_start[] asm("_binary_adf_music_mp3_start");
extern const uint8_t adf_music_mp3_end[] asm("_binary_adf_music_mp3_end");
static int adf_music_mp3_pos;
int mp3_music_read_cb(audio_element_handle_t el, char *buf, int len, TickType_t wait_time, void *ctx)
{
int read_size = adf_music_mp3_end - adf_music_mp3_start - adf_music_mp3_pos;
if (read_size == 0) {
return AEL_IO_DONE;
} else if (len
audio_pipeline_handle_t pipeline; // 管道
audio_element_handle_t i2s_stream_writer, mp3_decoder; // 音频元素
esp_log_level_set("*", ESP_LOG_WARN);
esp_log_level_set(TAG, ESP_LOG_INFO);
ESP_LOGI(TAG, "[ 1 ] Start audio codec chip");
audio_hal_codec_config_t audio_hal_codec_cfg = AUDIO_HAL_ES8388_DEFAULT();
audio_hal_handle_t hal = audio_hal_init(&audio_hal_codec_cfg, 0); // 初始化编解码驱动
audio_hal_ctrl_codec(hal, AUDIO_HAL_CODEC_MODE_DECODE, AUDIO_HAL_CTRL_START); // 启动解码
int player_volume;
audio_hal_get_volume(hal, &player_volume); // 获取音量
ESP_LOGI(TAG, "[ 2 ] Create audio pipeline, add all elements to pipeline, and subscribe pipeline event");
audio_pipeline_cfg_t pipeline_cfg = DEFAULT_AUDIO_PIPELINE_CONFIG();
pipeline = audio_pipeline_init(&pipeline_cfg); // 初始化管道
mem_assert(pipeline);
ESP_LOGI(TAG, "[2.1] Create mp3 decoder to decode mp3 file and set custom read callback");
mp3_decoder_cfg_t mp3_cfg = DEFAULT_MP3_DECODER_CONFIG();
mp3_decoder = mp3_decoder_init(&mp3_cfg); // 初始化mp3 decoder元素
audio_element_set_read_cb(mp3_decoder, mp3_music_read_cb, NULL);
ESP_LOGI(TAG, "[2.2] Create i2s stream to write data to codec chip");
i2s_stream_cfg_t i2s_cfg = I2S_STREAM_CFG_DEFAULT();
i2s_cfg.type = AUDIO_STREAM_WRITER;
i2s_stream_writer = i2s_stream_init(&i2s_cfg); // 初始化i2s stream元素
ESP_LOGI(TAG, "[2.3] Register all elements to audio pipeline"); // 注册元素到管道中去
audio_pipeline_register(pipeline, mp3_decoder, "mp3");
audio_pipeline_register(pipeline, i2s_stream_writer, "i2s");
ESP_LOGI(TAG, "[2.4] Link it together [mp3_music_read_cb]-->mp3_decoder-->i2s_stream-->[codec_chip]");
audio_pipeline_link(pipeline, (const char *[]) {"mp3", "i2s"}, 2); // 将mp3_music_read_cb mp3_decoder i2s_stream codec_chip关联在一起
ESP_LOGI(TAG, "[ 3 ] Initialize peripherals");
esp_periph_config_t periph_cfg = { 0 };
esp_periph_init(&periph_cfg);
ESP_LOGI(TAG, "[3.1] Initialize Touch peripheral");
periph_touch_cfg_t touch_cfg = {
.touch_mask = TOUCH_SEL_SET | TOUCH_SEL_PLAY | TOUCH_SEL_VOLUP | TOUCH_SEL_VOLDWN,
.tap_threshold_percent = 70,
};
esp_periph_handle_t touch_periph = periph_touch_init(&touch_cfg); // 初始化按键
ESP_LOGI(TAG, "[3.2] Start all peripherals");
esp_periph_start(touch_periph);
ESP_LOGI(TAG, "[ 4 ] Setup event listener");
audio_event_iface_cfg_t evt_cfg = AUDIO_EVENT_IFACE_DEFAULT_CFG();
audio_event_iface_handle_t evt = audio_event_iface_init(&evt_cfg);
ESP_LOGI(TAG, "[4.1] Listening event from all elements of pipeline");
audio_pipeline_set_listener(pipeline, evt); // 设置按键事件
ESP_LOGI(TAG, "[4.2] Listening event from peripherals"); // 设置外设监听事件
audio_event_iface_set_listener(esp_periph_get_event_iface(), evt);
ESP_LOGW(TAG, "[ 5 ] Tap touch buttons to control music player:");
ESP_LOGW(TAG, " [Play] to start, pause and resume, [Set] to stop.");
ESP_LOGW(TAG, " [Vol-] or [Vol+] to adjust volume.");
while (1) {
audio_event_iface_msg_t msg;
esp_err_t ret = audio_event_iface_listen(evt, &msg, portMAX_DELAY);
if (ret != ESP_OK) {
ESP_LOGE(TAG, "[ * ] Event interface error : %d", ret);
continue;
}
if (msg.source_type == AUDIO_ELEMENT_TYPE_ELEMENT && msg.source == (void *) mp3_decoder
&& msg.cmd == AEL_MSG_CMD_REPORT_MUSIC_INFO) {
audio_element_info_t music_info = {0};
audio_element_getinfo(mp3_decoder, &music_info);
ESP_LOGI(TAG, "[ * ] Receive music info from mp3 decoder, sample_rates=%d, bits=%d, ch=%d",
music_info.sample_rates, music_info.bits, music_info.channels);
audio_element_setinfo(i2s_stream_writer, &music_info);
i2s_stream_set_clk(i2s_stream_writer, music_info.sample_rates, music_info.bits, music_info.channels);
continue;
}
if (msg.source_type == PERIPH_ID_TOUCH
&& msg.cmd == PERIPH_TOUCH_TAP
&& msg.source == (void *)touch_periph) {
if ((int) msg.data == TOUCH_PLAY) { // 改变播放状态
ESP_LOGI(TAG, "[ * ] [Play] touch tap event");
audio_element_state_t el_state = audio_element_get_state(i2s_stream_writer);
switch (el_state) {
case AEL_STATE_INIT :
ESP_LOGI(TAG, "[ * ] Starting audio pipeline");
audio_pipeline_run(pipeline);
break;
case AEL_STATE_RUNNING :
ESP_LOGI(TAG, "[ * ] Pausing audio pipeline");
audio_pipeline_pause(pipeline);
break;
case AEL_STATE_PAUSED :
ESP_LOGI(TAG, "[ * ] Resuming audio pipeline");
audio_pipeline_resume(pipeline);
break;
case AEL_STATE_FINISHED :
ESP_LOGI(TAG, "[ * ] Rewinding audio pipeline");
audio_pipeline_stop(pipeline);
adf_music_mp3_pos = 0;
audio_pipeline_resume(pipeline);
break;
default :
ESP_LOGI(TAG, "[ * ] Not supported state %d", el_state);
}
} else if ((int) msg.data == TOUCH_SET) {
ESP_LOGI(TAG, "[ * ] [Set] touch tap event");
ESP_LOGI(TAG, "[ * ] Stopping audio pipeline");
break;
} else if ((int) msg.data == TOUCH_VOLUP) {
ESP_LOGI(TAG, "[ * ] [Vol+] touch tap event");
player_volume += 10;
if (player_volume > 100) {
player_volume = 100;
}
audio_hal_set_volume(hal, player_volume);
ESP_LOGI(TAG, "[ * ] Volume set to %d %%", player_volume);
} else if ((int) msg.data == TOUCH_VOLDWN) {
ESP_LOGI(TAG, "[ * ] [Vol-] touch tap event");
player_volume -= 10;
if (player_volume |