# ESP32 I2S Audio Processing Project

## Project Overview

This is an ESP32-based audio processing project that implements I2S (Inter-IC Sound) communication for capturing audio data using an ES7210 codec. The project includes functionality for:

- Audio recording to SD card in WAV format
- Automatic Speech Recognition (ASR) integration with cloud APIs
- WiFi connectivity for cloud services
- USB Mass Storage (MSC) for file access
- Power management and sleep modes
- Time synchronization via NTP

The project is built using the ESP-IDF (Espressif IoT Development Framework) and targets audio applications such as voice recorders, speech recognition systems, or audio processing units.

## Key Features

### Audio Recording
- I2S TDM (Time Division Multiplexing) interface with ES7210 codec
- Configurable sample rate (16kHz), bit width (16-bit), and stereo channels
- Direct Memory Access (DMA) for efficient audio data transfer
- WAV file format with proper headers
- Timestamp-based file naming for recordings

### Connectivity
- WiFi station mode for internet connectivity
- SD card mounting via SDMMC interface
- NTP time synchronization with multiple servers
- HTTP client for cloud API communication

### Cloud Integration
- ASR (Automatic Speech Recognition) using SiliconFlow API
- Audio transcription capabilities
- Secure HTTPS communication with bearer token authentication

### Power Management
- Dynamic CPU frequency scaling (8MHz to 240MHz)
- Light sleep mode for power conservation
- Automatic power management configuration

### USB Interface
- USB Mass Storage Class (MSC) implementation
- SD card access via USB when connected to host
- Console commands for file system operations

## Hardware Configuration

### I2S Interface
- Master clock (MCK): GPIO 38
- Bit clock (BCK): GPIO 14
- Word select (WS): GPIO 13
- Data in (DI): GPIO 12

### ES7210 Codec
- I2C interface: Port 0
- SDA: GPIO 1
- SCL: GPIO 2
- I2C address: 0x41

### SD Card Interface
- Command: GPIO 48
- Clock: GPIO 47
- Data 0: GPIO 21
- Mount point: `/sdcard`

### Additional Pins
- LED indicator: GPIO 48

## Building and Running

### Prerequisites
- ESP-IDF v4.x or later installed and configured
- ESP32 development board
- ES7210 I2S audio codec
- SD card

### Build Process
```bash
# Navigate to project directory
cd /path/to/esp32i2s

# Configure project (optional, if needed)
idf.py menuconfig

# Build the project
idf.py build

# Flash to ESP32
idf.py flash

# Monitor serial output
idf.py monitor
```

### Configuration Options
- Sample rate: 16000 Hz
- Channel count: 2 (Stereo)
- Bit width: 16 bits
- Recording duration: 20 seconds per file
- DMA buffer count: 8
- DMA buffer length: 512 samples

## File Structure

```
esp32i2s/
├── CMakeLists.txt          # Main build configuration
├── partitions.csv          # Partition table
├── sdkconfig              # SDK configuration
├── sdkconfig.defaults     # Default SDK settings
├── main/                  # Main application source
│   ├── main.c             # Main application entry point
│   ├── record.c/h         # Audio recording functionality
│   ├── asr.c/h            # Automatic Speech Recognition
│   ├── base.h             # Common definitions and includes
│   ├── format_wav.h       # WAV file format definitions
│   ├── usb_msc.c          # USB Mass Storage implementation
│   └── ...
└── ...
```

## Development Conventions

### Coding Style
- Follow ESP-IDF coding conventions
- Use ESP_LOG macros for logging
- Handle errors with ESP_ERROR_CHECK and ESP_RETURN_ON_FALSE
- Use FreeRTOS tasks for concurrent operations

### Memory Management
- Use DMA-capable memory allocation for I2S buffers
- Properly free allocated memory in error paths
- Monitor heap usage for memory leaks

### Power Efficiency
- Implement sleep modes when idle
- Use power management configuration appropriately
- Minimize active periods for battery operation

## Testing and Debugging

### Serial Monitor
Monitor the serial output for logging information:
- I2S initialization status
- SD card mounting results
- WiFi connection status
- Recording progress
- ASR API responses

### Console Commands
When USB MSC is active, the following console commands are available:
- `read` - Read README.MD file
- `write` - Create/update README.MD file
- `size` - Show storage capacity
- `expose` - Expose storage to USB host
- `status` - Show storage exposure status
- `exit` - Exit application

## Security Considerations

- WiFi credentials are hardcoded in `asr.c` (WIFI_SSID and WIFI_PASS)
- API token is hardcoded in `asr.c` (BEARER_TOKEN)
- HTTPS communication uses certificate validation
- Consider using NVS for storing sensitive information instead of hardcoding

## Known Issues and Limitations

- WiFi credentials and API tokens are hardcoded in source
- Recording duration is fixed at 20 seconds
- Only supports PCM WAV format
- Requires internet connectivity for ASR functionality
- USB MSC and file system access cannot be used simultaneously