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一、硬件原理

基于正点原子STM32F407探索者开发板，其中音频部分硬件原理图如下

其中WM8978是一款全功能音频处理器，STM32通过控制WM8978即可实现扬声器/喇叭的音频播放，麦克风的音频录制等功能。

主要控制两个接口

• IIC控制接口，实现WM8978寄存器的读写
• I2S数字音频接口，实现音频数据传输（接收和发送）

二、STM32CubeMX配置

2.1 RCC

开发板外接了两个晶振

• 8MHz的高速晶振
• 32.768kHz的低速晶振

2.2 SYS

Debug Serial Wire

2.3 I2C1

• GPIO口是PB8/PB9

2.4 USART1

• 用来打印调试日志，波特率调到1000000，加快日志打印
• Data Direction: Transmit Only
• DMA Settings: USART1_TX
• PA9 / PA10

2.5 USB_OTG_FS

• Mode:Device Only
• global interrupt 勾选

2.6 I2S2

• mode: Full-Duplex Master
• Audio Frequency: 48KHz
• DMA Setting: SPI2_TX / I2S2_EXT_RX
• GPIO Setting

2.7 USB_DEVICE

• Class For FS IP: Audio Device Class
• USBD_AUDIO_FREQ: 48000 sample/s
• 描述符有些部分可以自定义

2.8 Clock Configuration

2.9 Project Manager

• 堆栈调大0x4000

2.10 生成代码

• 右上角 GENERATE CODE

三、代码完善

3.1 WM8978

main.c

• main函数增加WM8978_Init();

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_I2C1_Init();
  MX_I2S2_Init();
  MX_USART1_UART_Init();
  MX_USB_DEVICE_Init();
  WM8978_Init();
  while (1)
  {
  }
}

wm8978.c

#define	DEVICE_ADDRESS						0x1A
#define	WIRTE_ADDRESS							(DEVICE_ADDRESS << 1 | 0)

extern I2C_HandleTypeDef hi2c1;

uint8_t WM8978_Write(uint8_t reg_addr, uint16_t data)
{
	uint8_t pData[10] =	{ 0 };

	pData[0] = (reg_addr << 1) | ((data >> 8) & 0x01);
	pData[1] = data & 0xFF;
	return HAL_I2C_Master_Transmit(&hi2c1, WIRTE_ADDRESS, pData, 2, 1000);
}

uint32_t WM8978_Init(void)
{
	WM8978_Reset();
	WM8978_Write(1, 0x0F);	// 模拟放大器使能， 使能输出输入缓存区
	WM8978_Write(3, 0x7F);	// 使能左右声道和L\ROUT2
	WM8978_Write(4, 0x10);	// I2S 16bit
	WM8978_Write(6, 0x00);	// MCU提供时钟
	WM8978_Write(10, 0x08);	// 输出音质最好
	WM8978_Write(43, 0x10);	// ROUT2反相
	WM8978_VolumeCtl(0x3F);
	return 0;
}

uint32_t WM8978_Reset(void)
{
	if(WM8978_Write(0, 0)!= HAL_OK)// 软复位
		return 1;
	HAL_Delay(10);
	return 0;
}

3.2 usbd_audio_if

• AUDIO_AudioCmd_FS中对应AUDIO_CMD_START、AUDIO_CMD_PLAY和AUDIO_CMD_STOP的操作
• HAL_I2S_TxCpltCallback对应传输完成的USB同步操作

extern I2S_HandleTypeDef hi2s2;
/**
  * @brief  Handles AUDIO command.
  * @param  pbuf: Pointer to buffer of data to be sent
  * @param  size: Number of data to be sent (in bytes)
  * @param  cmd: Command opcode
  * @retval USBD_OK if all operations are OK else USBD_FAIL
  */
static int8_t AUDIO_AudioCmd_FS(uint8_t* pbuf, uint32_t size, uint8_t cmd)
{
  switch(cmd)
  {
    case AUDIO_CMD_START:
		HAL_I2S_Transmit_DMA(&hi2s2, (uint16_t*)pbuf, size);
    break;

    case AUDIO_CMD_PLAY:
		HAL_I2S_Transmit_DMA(&hi2s2, (uint16_t*)pbuf, size);
    break;	

    case AUDIO_CMD_STOP:
    	HAL_I2S_DMAStop(&hi2s2);
    break;	
  }
  return (USBD_OK);
}

void HAL_I2S_TxHalfCpltCallback(I2S_HandleTypeDef *hi2s)
{
	HalfTransfer_CallBack_FS();
}

void HAL_I2S_TxCpltCallback(I2S_HandleTypeDef *hi2s)
{
	TransferComplete_CallBack_FS();
}

四、程序流程图

4.1 初始化流程

sequenceDiagram
main ->> main: HAL_Init();
main ->> main: SystemClock_Config();
main ->> main: HAL_Delay(100);
main ->> main: MX_GPIO_Init();
main ->> main: MX_DMA_Init();
main ->> main: MX_I2C1_Init();
main ->> hal库: HAL_I2C_Init();
hal库->> stm32f4xx_hal_map: HAL_I2C_MspInit();
stm32f4xx_hal_map-->>hal库: 
hal库-->>main : 
main ->> main: MX_I2S2_Init();
main ->> hal库: HAL_I2S_Init();
hal库->> stm32f4xx_hal_map: HAL_I2S_MspInit();
stm32f4xx_hal_map-->>hal库: 
hal库-->>main : 
main ->> wx8978: WM8978_Init();
main ->> usb_device: MX_USB_DEVICE_Init();
usb_device->> STM32_USB_DEVICE_Library: USBD_Init(&hUsbDeviceFS, &FS_Desc, DEVICE_FS);
usb_device->> STM32_USB_DEVICE_Library: USBD_RegisterClass(&hUsbDeviceFS, &USBD_AUDIO);
usb_device->> STM32_USB_DEVICE_Library: USBD_AUDIO_RegisterInterface(&hUsbDeviceFS, &USBD_AUDIO_fops_FS);
usb_device->> STM32_USB_DEVICE_Library: USBD_Start(&hUsbDeviceFS);
main ->> main: HAL_Delay(100);
main ->> main: while(1);

4.2 播放流程

sequenceDiagram
STM32_USB_DEVICE_Library->> usbd_audio_if: AudioCmd(uint8_t *pbuf, uint32_t size, uint8_t cmd)
usbd_audio_if->>hal库: HAL_I2S_Transmit_DMA

觉得好，就一键三连呗（点赞+收藏+关注）