STM32 besitzt je nach Chipvariante eine serielle Audio-Schnittstelle SAI. Durch diese Schnittstelle kann über übliche Protokolle mit Audio-Codecs kommuniziert werden.

Audio-Clocks

Das Codec und die SAI-Schnittstelle müssen synchronisiert werden. Dabei gibt es konkrete Vorgaben bzw. Randbedingungen seitens Codecs.

Audio-Abtastfrequenz $F_s$ wählen.
Den Multiplikator $k_{MCLK}$ (Codecs haben oft Multiplikatortabellen z.B. 256 oder 512 bei 48kHz) wählen.
Daraus die erforderliche Master-Clock-Frequenz berechnen. (Oft $F_{MCLK}F_s \cdot k_{MCLK}$ )
Master-Clock-Quelle konfigurieren (Externer Quarz bzw. interne Clockquellen)

Übertragung

Unter dem Aspekt gibt es (wie für viele andere Hardwarekomponenten) hauptsächlich drei Möglichkeiten eine Codec-Schnittstelle zu steuern bzw. auszulesen:

Normaler Modus (Blockierend)
Interrupt-Modus (Nicht-blockierend)
Per DMA auslesen (Nicht-blockierend)

Bei einer echtzeitkritischen Audio-DSP-Anwendung kommt nur DMA-Schnittstelle in Frage. Die Konfiguration der Software und Hardware ist hier beschrieben.

SAI und DMA Konfiguration

Beim Flex 500 ist feste 48kHz Abtastrate gewählt. Bei CS4272 kann der Multiplikator 256 oder 512 gewählt werden. Um auch zukünftig 96kHz zu unterstützen wurde hierbei 512 gewählt. Zu Stabilitätszwecken wurde für einen externen Quarz entschieden. Die Frequenz des Quarzes berechnet sich also als

(1) $\begin{equation*} F_{MCLK}=F_S \cdot k_{MCLK} = 48000 \cdot 512 = 24,576 MHz \end{equation*}$

In dem Fall ist der Codec der Master und generiert den Bitclock. Der DSP ist Slave und erhält den Bitclock und dazugehörige Streams.

Die Konfiguration sieht folgendermaßen aus:

Low level Treiber: (*_hal_msp.c)

void HAL_SAI_MspInit(SAI_HandleTypeDef* hsai)
{

  GPIO_InitTypeDef GPIO_InitStruct;
/* SAI1 */
    if(hsai->Instance==SAI1_Block_A)
    {
    /* Peripheral clock enable */
    if (SAI1_client == 0)
    {
       __HAL_RCC_SAI1_CLK_ENABLE();
    }
    SAI1_client ++;
    
    /**SAI1_A_Block_A GPIO Configuration    
    PE4     ------> SAI1_FS_A
    PE5     ------> SAI1_SCK_A
    PE6     ------> SAI1_SD_A 
    */
    GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;
    HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

    /* Peripheral DMA init*/
    /* DMA controller clock enable */
    __HAL_RCC_DMA2_CLK_ENABLE();
    
    hdma_sai1_a.Instance = DMA2_Stream1;
    hdma_sai1_a.Init.Request = DMA_REQUEST_SAI1_A;
    hdma_sai1_a.Init.Direction = DMA_PERIPH_TO_MEMORY;
    hdma_sai1_a.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_sai1_a.Init.MemInc = DMA_MINC_ENABLE;
    hdma_sai1_a.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;
    hdma_sai1_a.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;
    hdma_sai1_a.Init.Mode = DMA_CIRCULAR;
    hdma_sai1_a.Init.Priority = DMA_PRIORITY_HIGH;
    hdma_sai1_a.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
//    hdma_sai1_a.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_HALFFULL;
//	hdma_sai1_a.Init.MemBurst = DMA_MBURST_SINGLE;
//	hdma_sai1_a.Init.PeriphBurst = DMA_PBURST_SINGLE;
    if (HAL_DMA_Init(&hdma_sai1_a) != HAL_OK)
    {
//      _Error_Handler(__FILE__, __LINE__);
    }

    /* DMA2_Stream1_IRQn interrupt configuration */
    HAL_NVIC_SetPriority(DMA2_Stream1_IRQn, 1, 0);
    HAL_NVIC_EnableIRQ(DMA2_Stream1_IRQn);

    /* Several peripheral DMA handle pointers point to the same DMA handle.
     Be aware that there is only one channel to perform all the requested DMAs. */
    __HAL_LINKDMA(hsai,hdmarx,hdma_sai1_a);

    __HAL_LINKDMA(hsai,hdmatx,hdma_sai1_a);

    }
    if(hsai->Instance==SAI1_Block_B)
    {
      /* Peripheral clock enable */
      if (SAI1_client == 0)
      {
       __HAL_RCC_SAI1_CLK_ENABLE();
      }
    SAI1_client ++;
    
    /**SAI1_B_Block_B GPIO Configuration    
    PE3     ------> SAI1_SD_B 
    */
    GPIO_InitStruct.Pin = GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;
    HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

    /* Peripheral DMA init*/
    
    hdma_sai1_b.Instance = DMA2_Stream0;
    hdma_sai1_b.Init.Request = DMA_REQUEST_SAI1_B;
    hdma_sai1_b.Init.Direction = DMA_MEMORY_TO_PERIPH;
    hdma_sai1_b.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_sai1_b.Init.MemInc = DMA_MINC_ENABLE;
    hdma_sai1_b.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;
    hdma_sai1_b.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;
    hdma_sai1_b.Init.Mode = DMA_CIRCULAR;
    hdma_sai1_b.Init.Priority = DMA_PRIORITY_HIGH;
    hdma_sai1_b.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
//    hdma_sai1_b.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_HALFFULL;
//    hdma_sai1_b.Init.MemBurst = DMA_MBURST_SINGLE;
//    hdma_sai1_b.Init.PeriphBurst = DMA_PBURST_SINGLE;
    if (HAL_DMA_Init(&hdma_sai1_b) != HAL_OK)
    {
//      _Error_Handler(__FILE__, __LINE__);
    }

    /* DMA interrupt init */
    /* DMA2_Stream0_IRQn interrupt configuration */
    HAL_NVIC_SetPriority(DMA2_Stream0_IRQn, 1, 0);
    HAL_NVIC_EnableIRQ(DMA2_Stream0_IRQn);

    /* Several peripheral DMA handle pointers point to the same DMA handle.
     Be aware that there is only one channel to perform all the requested DMAs. */
    __HAL_LINKDMA(hsai,hdmarx,hdma_sai1_b);
    __HAL_LINKDMA(hsai,hdmatx,hdma_sai1_b);
    }
}

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void HAL_SAI_MspInit(SAI_HandleTypeDef* hsai)

{

GPIO_InitTypeDef GPIO_InitStruct;

/* SAI1 */

if(hsai->Instance==SAI1_Block_A)

{

/* Peripheral clock enable */

if (SAI1_client == 0)

{

__HAL_RCC_SAI1_CLK_ENABLE();

}

SAI1_client ++;

/**SAI1_A_Block_A GPIO Configuration

PE4 ------> SAI1_FS_A

PE5 ------> SAI1_SCK_A

PE6 ------> SAI1_SD_A

GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6;

GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;

GPIO_InitStruct.Pull = GPIO_NOPULL;

GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;

GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;

HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

/* Peripheral DMA init*/

/* DMA controller clock enable */

__HAL_RCC_DMA2_CLK_ENABLE();

hdma_sai1_a.Instance = DMA2_Stream1;

hdma_sai1_a.Init.Request = DMA_REQUEST_SAI1_A;

hdma_sai1_a.Init.Direction = DMA_PERIPH_TO_MEMORY;

hdma_sai1_a.Init.PeriphInc = DMA_PINC_DISABLE;

hdma_sai1_a.Init.MemInc = DMA_MINC_ENABLE;

hdma_sai1_a.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;

hdma_sai1_a.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;

hdma_sai1_a.Init.Mode = DMA_CIRCULAR;

hdma_sai1_a.Init.Priority = DMA_PRIORITY_HIGH;

hdma_sai1_a.Init.FIFOMode = DMA_FIFOMODE_DISABLE;

// hdma_sai1_a.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_HALFFULL;

// hdma_sai1_a.Init.MemBurst = DMA_MBURST_SINGLE;

// hdma_sai1_a.Init.PeriphBurst = DMA_PBURST_SINGLE;

if (HAL_DMA_Init(&hdma_sai1_a) != HAL_OK)

{

// _Error_Handler(__FILE__, __LINE__);

}

/* DMA2_Stream1_IRQn interrupt configuration */

HAL_NVIC_SetPriority(DMA2_Stream1_IRQn, 1, 0);

HAL_NVIC_EnableIRQ(DMA2_Stream1_IRQn);

/* Several peripheral DMA handle pointers point to the same DMA handle.

Be aware that there is only one channel to perform all the requested DMAs. */

__HAL_LINKDMA(hsai,hdmarx,hdma_sai1_a);

__HAL_LINKDMA(hsai,hdmatx,hdma_sai1_a);

}

if(hsai->Instance==SAI1_Block_B)

{

/* Peripheral clock enable */

if (SAI1_client == 0)

{

__HAL_RCC_SAI1_CLK_ENABLE();

}

SAI1_client ++;

/**SAI1_B_Block_B GPIO Configuration

PE3 ------> SAI1_SD_B

GPIO_InitStruct.Pin = GPIO_PIN_3;

GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;

GPIO_InitStruct.Pull = GPIO_NOPULL;

GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;

GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;

HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

/* Peripheral DMA init*/

hdma_sai1_b.Instance = DMA2_Stream0;

hdma_sai1_b.Init.Request = DMA_REQUEST_SAI1_B;

hdma_sai1_b.Init.Direction = DMA_MEMORY_TO_PERIPH;

hdma_sai1_b.Init.PeriphInc = DMA_PINC_DISABLE;

hdma_sai1_b.Init.MemInc = DMA_MINC_ENABLE;

hdma_sai1_b.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;

hdma_sai1_b.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;

hdma_sai1_b.Init.Mode = DMA_CIRCULAR;

hdma_sai1_b.Init.Priority = DMA_PRIORITY_HIGH;

hdma_sai1_b.Init.FIFOMode = DMA_FIFOMODE_DISABLE;

// hdma_sai1_b.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_HALFFULL;

// hdma_sai1_b.Init.MemBurst = DMA_MBURST_SINGLE;

// hdma_sai1_b.Init.PeriphBurst = DMA_PBURST_SINGLE;

if (HAL_DMA_Init(&hdma_sai1_b) != HAL_OK)

{

// _Error_Handler(__FILE__, __LINE__);

}

/* DMA interrupt init */

/* DMA2_Stream0_IRQn interrupt configuration */

HAL_NVIC_SetPriority(DMA2_Stream0_IRQn, 1, 0);

HAL_NVIC_EnableIRQ(DMA2_Stream0_IRQn);

/* Several peripheral DMA handle pointers point to the same DMA handle.

Be aware that there is only one channel to perform all the requested DMAs. */

__HAL_LINKDMA(hsai,hdmarx,hdma_sai1_b);

__HAL_LINKDMA(hsai,hdmatx,hdma_sai1_b);

}

SAI Konfiguration

void c_sai::MX_SAI1_Init(void)
{

  hsai_BlockA1.Instance = SAI1_Block_A;
  hsai_BlockA1.Init.AudioMode = SAI_MODESLAVE_RX;
  hsai_BlockA1.Init.Synchro = SAI_ASYNCHRONOUS;
  hsai_BlockA1.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;
  hsai_BlockA1.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;
hsai_BlockA1.Init.AudioFrequency = SAI_AUDIO_FREQUENCY_48K;
  hsai_BlockA1.Init.SynchroExt = SAI_SYNCEXT_OUTBLOCKA_ENABLE;
  hsai_BlockA1.Init.MonoStereoMode = SAI_STEREOMODE;
  hsai_BlockA1.Init.CompandingMode = SAI_NOCOMPANDING;
  hsai_BlockA1.Init.TriState = SAI_OUTPUT_NOTRELEASED;
  if (HAL_SAI_InitProtocol(&hsai_BlockA1, SAI_I2S_STANDARD, SAI_PROTOCOL_DATASIZE_32BIT, 2) != HAL_OK)
  {
//    _Error_Handler(__FILE__, __LINE__);
  }

  hsai_BlockB1.Instance = SAI1_Block_B;
  hsai_BlockB1.Init.AudioMode = SAI_MODESLAVE_TX;
  hsai_BlockB1.Init.Synchro = SAI_SYNCHRONOUS;
  hsai_BlockB1.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;
  hsai_BlockB1.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;
  hsai_BlockB1.Init.SynchroExt = SAI_SYNCEXT_DISABLE;
  hsai_BlockB1.Init.MonoStereoMode = SAI_STEREOMODE;
  hsai_BlockB1.Init.CompandingMode = SAI_NOCOMPANDING;
  hsai_BlockB1.Init.TriState = SAI_OUTPUT_NOTRELEASED;
  if (HAL_SAI_InitProtocol(&hsai_BlockB1, SAI_I2S_STANDARD, SAI_PROTOCOL_DATASIZE_32BIT, 2) != HAL_OK)
  {
//    _Error_Handler(__FILE__, __LINE__);
  }

}

void c_sai::MX_SAI1_Init(void)

{

hsai_BlockA1.Instance = SAI1_Block_A;

hsai_BlockA1.Init.AudioMode = SAI_MODESLAVE_RX;

hsai_BlockA1.Init.Synchro = SAI_ASYNCHRONOUS;

hsai_BlockA1.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;

hsai_BlockA1.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;

hsai_BlockA1.Init.AudioFrequency = SAI_AUDIO_FREQUENCY_48K;

hsai_BlockA1.Init.SynchroExt = SAI_SYNCEXT_OUTBLOCKA_ENABLE;

hsai_BlockA1.Init.MonoStereoMode = SAI_STEREOMODE;

hsai_BlockA1.Init.CompandingMode = SAI_NOCOMPANDING;

hsai_BlockA1.Init.TriState = SAI_OUTPUT_NOTRELEASED;

if (HAL_SAI_InitProtocol(&hsai_BlockA1, SAI_I2S_STANDARD, SAI_PROTOCOL_DATASIZE_32BIT, 2) != HAL_OK)

{

// _Error_Handler(__FILE__, __LINE__);

}

hsai_BlockB1.Instance = SAI1_Block_B;

hsai_BlockB1.Init.AudioMode = SAI_MODESLAVE_TX;

hsai_BlockB1.Init.Synchro = SAI_SYNCHRONOUS;

hsai_BlockB1.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;

hsai_BlockB1.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;

hsai_BlockB1.Init.SynchroExt = SAI_SYNCEXT_DISABLE;

hsai_BlockB1.Init.MonoStereoMode = SAI_STEREOMODE;

hsai_BlockB1.Init.CompandingMode = SAI_NOCOMPANDING;

hsai_BlockB1.Init.TriState = SAI_OUTPUT_NOTRELEASED;

if (HAL_SAI_InitProtocol(&hsai_BlockB1, SAI_I2S_STANDARD, SAI_PROTOCOL_DATASIZE_32BIT, 2) != HAL_OK)

{

// _Error_Handler(__FILE__, __LINE__);

}

Starten vom Treiber

void c_sai::start(void){

	//Start SAI and DMA Streams
	printf("Initializing SAI DMA Receive stream...\n");
//	printf("Initializing SAI DMA Receive stream...\n");
	HAL_SAI_Receive_DMA(&hsai_BlockA1, (uint8_t*)&rx_buf, 4*buf_size);
	printf("SAI DMA Receive stream initialized!\n");
//	printf("Initializing SAI DMA transmit stream...\n");
	HAL_SAI_Transmit_DMA(&hsai_BlockB1, (uint8_t*)&tx_buf, 4*buf_size);
	printf("SAI DMA transmit stream initialized!\n");

}

void c_sai::start(void){

//Start SAI and DMA Streams

printf("Initializing SAI DMA Receive stream...\n");

// printf("Initializing SAI DMA Receive stream...\n");

HAL_SAI_Receive_DMA(&hsai_BlockA1, (uint8_t*)&rx_buf, 4*buf_size);

printf("SAI DMA Receive stream initialized!\n");

// printf("Initializing SAI DMA transmit stream...\n");

HAL_SAI_Transmit_DMA(&hsai_BlockB1, (uint8_t*)&tx_buf, 4*buf_size);

printf("SAI DMA transmit stream initialized!\n");

}

DMA Interrupts setzen die Flags. Die Software Architektur ist hier beschrieben.

void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)
{
	tx_status=0;
}


void HAL_SAI_TxHalfCpltCallback(SAI_HandleTypeDef *hsai){
	tx_status=1;
}

void HAL_SAI_RxCpltCallback(SAI_HandleTypeDef *hsai){
	rx_status=0;
}

void HAL_SAI_RxHalfCpltCallback(SAI_HandleTypeDef *hsai){
	rx_status=1;
}

void HAL_SAI_TxCpltCallback(SAI_HandleTypeDef *hsai)

{

tx_status=0;

}

void HAL_SAI_TxHalfCpltCallback(SAI_HandleTypeDef *hsai){

tx_status=1;

}

void HAL_SAI_RxCpltCallback(SAI_HandleTypeDef *hsai){

rx_status=0;

}

void HAL_SAI_RxHalfCpltCallback(SAI_HandleTypeDef *hsai){

rx_status=1;

}

Die CODEC-Treiber sind hier beschrieben:

CS4272 CODEC-Schnittstelle für Nucleo H743

WM8731 CODEC-Schnittstelle für Nucleo H743

Ressourcen

Der vollständige Code vom Communication Stack befindet sich auf den Repositories vom Controller und DSP unter den Ordnern „hw„.

DSP – Targetcode vom herunterladen

Controller- Targetcode vom herunterladen

Can Kosar

STM32 SAI Konfiguration

Audio-Clocks

Übertragung

SAI und DMA Konfiguration

Ressourcen

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