STM32F746G-Disco开发板上带有数字麦克风和音频输出，它们组合起来就可以实现助听器的功能。只要把麦克风的输入信号进行放大，然后在通过音频接口输出。
下面程序演示了助听器的功能，它来自Mbed例程。首先它通过数字麦克风（U21、U22）获取环境声音，将数据保存到接收缓冲区，然后将数字音频发送到音频输出（U11）。如果我们在CN10（音频输出）上接一个耳机或者扬声器，就可以清楚的听到放大后的环境声音，效果非常不错。在连接耳机时，需要注意保护耳朵，因为开发板上没有音量控制的旋钮，不能调节音量。
#include "mbed.h"
#include "AUDIO_DISCO_F746NG.h"
#include "SDRAM_DISCO_F746NG.h"
AUDIO_DISCO_F746NG audio;
// audio IN_OUT buffer is stored in the SDRAM, SDRAM needs to be initialized
// and FMC enabled
SDRAM_DISCO_F746NG sdram;
DigitalOut led_green(LED1);
DigitalOut led_red(LED2);
Serial pc(USBTX, USBRX);
typedef enum
{
BUFFER_OFFSET_NONE = 0,
BUFFER_OFFSET_HALF = 1,
BUFFER_OFFSET_FULL = 2,
}BUFFER_StateTypeDef;
#define AUDIO_BLOCK_SIZE ((uint32_t)512)
#define AUDIO_BUFFER_IN SDRAM_DEVICE_ADDR /* In SDRAM */
#define AUDIO_BUFFER_OUT (SDRAM_DEVICE_ADDR + (AUDIO_BLOCK_SIZE * 2)) /* In SDRAM */
__IO uint32_t audio_rec_buffer_state = BUFFER_OFFSET_NONE;
static uint8_t SetSysClock_PLL_HSE_200MHz();
int main()
{
SetSysClock_PLL_HSE_200MHz();
pc.baud(9600);
pc.printf("\n\nAUDIO LOOPBACK EXAMPLE START:\n");
led_red = 0;
pc.printf("\nAUDIO RECORD INIT OK\n");
pc.printf("Microphones sound streamed to headphones\n");
/* Initialize SDRAM buffers */
memset((uint16_t*)AUDIO_BUFFER_IN, 0, AUDIO_BLOCK_SIZE*2);
memset((uint16_t*)AUDIO_BUFFER_OUT, 0, AUDIO_BLOCK_SIZE*2);
audio_rec_buffer_state = BUFFER_OFFSET_NONE;
/* Start Recording */
audio.IN_Record((uint16_t*)AUDIO_BUFFER_IN, AUDIO_BLOCK_SIZE);
/* Start Playback */
audio.OUT_SetAudioFrameSlot(CODEC_AUDIOFRAME_SLOT_02);
audio.OUT_Play((uint16_t*)AUDIO_BUFFER_OUT, AUDIO_BLOCK_SIZE * 2);
while (1) {
/* Wait end of half block recording */
while(audio_rec_buffer_state == BUFFER_OFFSET_HALF) {
}
audio_rec_buffer_state = BUFFER_OFFSET_NONE;
/* Copy recorded 1st half block */
memcpy((uint16_t *)(AUDIO_BUFFER_OUT), (uint16_t *)(AUDIO_BUFFER_IN), AUDIO_BLOCK_SIZE);
/* Wait end of one block recording */
while(audio_rec_buffer_state == BUFFER_OFFSET_FULL) {
}
audio_rec_buffer_state = BUFFER_OFFSET_NONE;
/* Copy recorded 2nd half block */
memcpy((uint16_t *)(AUDIO_BUFFER_OUT + (AUDIO_BLOCK_SIZE)), (uint16_t *)(AUDIO_BUFFER_IN
+ (AUDIO_BLOCK_SIZE)), AUDIO_BLOCK_SIZE);
}
}
/*-------------------------------------------------------------------------------------
Callbacks implementation:
the callbacks API are defined __weak in the stm32746g_discovery_audio.c file
and their implementation should be done in the user code if they are needed.
Below some examples of callback implementations.
-------------------------------------------------------------------------------------*/
/**
* [url=home.php?mod=space&uid=247401]@brief[/url] Manages the DMA Transfer complete interrupt.
* @param None
* @retval None
*/
void BSP_AUDIO_IN_TransferComplete_CallBack(void)
{
audio_rec_buffer_state = BUFFER_OFFSET_FULL;
return;
}
/**
* @brief Manages the DMA Half Transfer complete interrupt.
* @param None
* @retval None
*/
void BSP_AUDIO_IN_HalfTransfer_CallBack(void)
{
audio_rec_buffer_state = BUFFER_OFFSET_HALF;
return;
}
- 首先定义缓冲区大小和音频输入输出缓冲区
#define AUDIO_BLOCK_SIZE ((uint32_t)512)
#define AUDIO_BUFFER_IN SDRAM_DEVICE_ADDR /* In SDRAM */
#define AUDIO_BUFFER_OUT (SDRAM_DEVICE_ADDR + (AUDIO_BLOCK_SIZE * 2)) /* In SDRAM */ - 然后进行初始化，初始化部分完成下面几个功能：
- 分配缓冲区
/* Initialize SDRAM buffers */
memset((uint16_t*)AUDIO_BUFFER_IN, 0, AUDIO_BLOCK_SIZE*2);
memset((uint16_t*)AUDIO_BUFFER_OUT, 0, AUDIO_BLOCK_SIZE*2); - 启用录音功能，将音频输入保存到输入缓冲区
/* Start Recording */
audio.IN_Record((uint16_t*)AUDIO_BUFFER_IN, AUDIO_BLOCK_SIZE); - 设置音频回放
audio.OUT_SetAudioFrameSlot(CODEC_AUDIOFRAME_SLOT_02);
audio.OUT_Play((uint16_t*)AUDIO_BUFFER_OUT, AUDIO_BLOCK_SIZE * 2);
- 在主循环中，等待音频输入完成，然后将输入缓冲区（AUDIO_BUFFER_IN）的数据复制到输出（AUDIO_BUFFER_OUT）缓冲区。音频输入的录音和回放，都是使用DMA方式自动完成的，所以无需CPU处理。
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