v1.8.0: Audio 代码重构与低功耗优化 (#943)

* Reconstruct Audio Code

* Remove old IoT implementation

* Add MQTT-UDP documentation

* OTA升级失败时，可以继续使用

main/audio/audio_codec.h

@@ -0,0 +1,59 @@
+#ifndef _AUDIO_CODEC_H
+#define _AUDIO_CODEC_H
+
+#include <freertos/FreeRTOS.h>
+#include <freertos/event_groups.h>
+#include <driver/i2s_std.h>
+
+#include <vector>
+#include <string>
+#include <functional>
+
+#include "board.h"
+
+#define AUDIO_CODEC_DMA_DESC_NUM 6
+#define AUDIO_CODEC_DMA_FRAME_NUM 240
+#define AUDIO_CODEC_DEFAULT_MIC_GAIN 30.0
+
+class AudioCodec {
+public:
+    AudioCodec();
+    virtual ~AudioCodec();
+    
+    virtual void SetOutputVolume(int volume);
+    virtual void EnableInput(bool enable);
+    virtual void EnableOutput(bool enable);
+
+    virtual void OutputData(std::vector<int16_t>& data);
+    virtual bool InputData(std::vector<int16_t>& data);
+    virtual void Start();
+
+    inline bool duplex() const { return duplex_; }
+    inline bool input_reference() const { return input_reference_; }
+    inline int input_sample_rate() const { return input_sample_rate_; }
+    inline int output_sample_rate() const { return output_sample_rate_; }
+    inline int input_channels() const { return input_channels_; }
+    inline int output_channels() const { return output_channels_; }
+    inline int output_volume() const { return output_volume_; }
+    inline bool input_enabled() const { return input_enabled_; }
+    inline bool output_enabled() const { return output_enabled_; }
+
+protected:
+    i2s_chan_handle_t tx_handle_ = nullptr;
+    i2s_chan_handle_t rx_handle_ = nullptr;
+
+    bool duplex_ = false;
+    bool input_reference_ = false;
+    bool input_enabled_ = false;
+    bool output_enabled_ = false;
+    int input_sample_rate_ = 0;
+    int output_sample_rate_ = 0;
+    int input_channels_ = 1;
+    int output_channels_ = 1;
+    int output_volume_ = 70;
+
+    virtual int Read(int16_t* dest, int samples) = 0;
+    virtual int Write(const int16_t* data, int samples) = 0;
+};
+
+#endif // _AUDIO_CODEC_H