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STM32N6 Nucleo audio input using SAI with GPDMA

jweber
Associate

‎2025-08-21 9:05 AM

Hello everyone,

I'm trying to configure the SAI and GPDMA peripherals on an STM32 to acquire audio from an I2S microphone. My goal is to capture a 32-bit, 2-channel audio stream at a 16 kHz sample rate, with the STM32 acting as the clock master. I've followed the steps below, but I'm running into two main issues:

  • While the HAL_SAI_RxCpltCallback and HAL_SAI_RxHalfCpltCallback functions are being called, the acquisition buffer remains unchanged (full of zeros).
  • I'm seeing a 16 kHz signal on all three I2S lines (SCK, FS, and SD), which is incorrect. The clock (SCK) should be much higher.

Here's a summary of the steps I've taken:

  • PLL4 Configuration: I've configured PLL4 to generate a 1.024 MHz clock (16 kHz * 64 = 1.024 MHz). This clock feeds into the IC7 peripheral.
  • GPDMA1 Configuration: I've enabled the clock and interrupts for GPDMA1 Channel 0 and added a linked-list initialization.
  • SAI1 Block B1 Configuration: I've set up the SAI handle for I2S standard, 32-bit data, 16 kHz audio frequency, Master RX Asynchronous mode, and 2 channels.
  • SAI MSP Configuration (HAL_SAI_MspInit):
    • I've configured the SAI clock source to use PLL4 via IC7.
    • The necessary GPIOs (SCK, SD, FS) have been initialized.
    • I've enabled NVIC for SAI1_B.
    • I've configured the DMA node for the SAI1_B peripheral, adding it to the queue in circular mode.
    • I've linked the DMA queue to the DMA channel and associated the SAI handle with the DMA.
  • Interrupt Handlers: I've overwritten the global interrupt handlers for GPDMA1_Channel0 and SAI1_B.
  • Callbacks: I've implemented the HAL_SAI_RxCpltCallback and HAL_SAI_RxHalfCpltCallback functions.
  • DMA Attributes: I've set the security and attribute configurations for GPDMA Channel 0.
  • Data Reception: I'm calling HAL_SAI_Receive_DMA to start the acquisition.

I've attached part of my code snippets below.

/**
  * @brief GPDMA1 Initialization Function
  * @PAram None
  * @retval None
  */
static void MX_GPDMA1_Init(void)
{

  /* Peripheral clock enable */
  __HAL_RCC_GPDMA1_CLK_ENABLE();

  /* GPDMA1 interrupt Init */
    HAL_NVIC_SetPriority(GPDMA1_Channel0_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(GPDMA1_Channel0_IRQn);
}

/**
  * @brief SAI1 Initialization Function
  * @PAram None
  * @retval None
  */
static void MX_SAI1_Init(void)
{

    /* DMA node configuration declaration */
  hsai_BlockB1.Instance = SAI1_Block_B;
  hsai_BlockB1.Init.AudioMode = SAI_MODEMASTER_RX;
  hsai_BlockB1.Init.Synchro = SAI_ASYNCHRONOUS;
  hsai_BlockB1.Init.OutputDrive = SAI_OUTPUTDRIVE_DISABLE;
  hsai_BlockB1.Init.NoDivider = SAI_MASTERDIVIDER_ENABLE;
  hsai_BlockB1.Init.FIFOThreshold = SAI_FIFOTHRESHOLD_EMPTY;
  hsai_BlockB1.Init.AudioFrequency = SAI_AUDIO_FREQUENCY_16K;
  hsai_BlockB1.Init.SynchroExt = SAI_SYNCEXT_DISABLE;
  hsai_BlockB1.Init.MckOutput = SAI_MCK_OUTPUT_ENABLE;
  hsai_BlockB1.Init.MonoStereoMode = SAI_STEREOMODE;
  hsai_BlockB1.Init.CompandingMode = SAI_NOCOMPANDING;
  if (HAL_SAI_InitProtocol(&hsai_BlockB1, SAI_I2S_STANDARD, SAI_PROTOCOL_DATASIZE_32BIT, 2) != HAL_OK)
  {
    Error_Handler();
  }
    
}


void HAL_SAI_MspInit(SAI_HandleTypeDef* hsai)
{

  GPIO_InitTypeDef GPIO_InitStruct;
  DMA_NodeConfTypeDef NodeConfig;
  RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};
/* SAI1 */
    if(hsai->Instance==SAI1_Block_B)
    {
      /* Peripheral clock enable */

  /** Initializes the peripherals clock
  */
    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SAI1;
    PeriphClkInitStruct.Sai1ClockSelection = RCC_SAI1CLKSOURCE_IC7;
    PeriphClkInitStruct.ICSelection[RCC_IC7].ClockSelection = RCC_ICCLKSOURCE_PLL4;
    PeriphClkInitStruct.ICSelection[RCC_IC7].ClockDivider = 250;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
    {
      Error_Handler();
    }

      if (SAI1_client == 0)
      {
       __HAL_RCC_SAI1_CLK_ENABLE();
      }
    SAI1_client ++;

    __HAL_RCC_GPIOG_CLK_ENABLE();
    __HAL_RCC_GPIOA_CLK_ENABLE();

    /**SAI1_B_Block_B GPIO Configuration
    PG1     ------> SAI1_SCK_B
    PA3     ------> SAI1_SD_B
    PG2     ------> SAI1_FS_B
    */
    GPIO_InitStruct.Pin = GPIO_PIN_1|GPIO_PIN_2;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;
    HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF6_SAI1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);


    HAL_NVIC_SetPriority(SAI1_B_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(SAI1_B_IRQn);

    /* Peripheral DMA init*/
    NodeConfig.NodeType = DMA_GPDMA_LINEAR_NODE;
    NodeConfig.Init.Request = GPDMA1_REQUEST_SAI1_B;
    NodeConfig.Init.BlkHWRequest = DMA_BREQ_SINGLE_BURST;
    NodeConfig.Init.Direction = DMA_PERIPH_TO_MEMORY;
    NodeConfig.Init.SrcInc = DMA_SINC_FIXED;
    NodeConfig.Init.DestInc = DMA_DINC_FIXED;
    NodeConfig.Init.SrcDataWidth = DMA_SRC_DATAWIDTH_WORD;
    NodeConfig.Init.DestDataWidth = DMA_DEST_DATAWIDTH_WORD;
    NodeConfig.Init.SrcBurstLength = 1;
    NodeConfig.Init.DestBurstLength = 1;
    NodeConfig.Init.TransferAllocatedPort = DMA_SRC_ALLOCATED_PORT0|DMA_DEST_ALLOCATED_PORT0;
    NodeConfig.Init.TransferEventMode = DMA_TCEM_BLOCK_TRANSFER;
    NodeConfig.Init.Mode = DMA_NORMAL;
    NodeConfig.TriggerConfig.TriggerPolarity = DMA_TRIG_POLARITY_MASKED;
    NodeConfig.TriggerConfig.TriggerSelection = GPDMA1_TRIGGER_GPDMA1_CH0_TCF;
    NodeConfig.DataHandlingConfig.DataExchange = DMA_EXCHANGE_NONE;
    NodeConfig.DataHandlingConfig.DataAlignment = DMA_DATA_RIGHTALIGN_ZEROPADDED;
    NodeConfig.SrcSecure = DMA_CHANNEL_SRC_SEC;
    NodeConfig.DestSecure = DMA_CHANNEL_DEST_SEC;
    if (HAL_DMAEx_List_BuildNode(&NodeConfig, &Node_GPDMA1_Channel0) != HAL_OK)
    {
      Error_Handler();
    }

    if (HAL_DMAEx_List_InsertNode(&List_GPDMA1_Channel0, NULL, &Node_GPDMA1_Channel0) != HAL_OK)
    {
      Error_Handler();
    }

    if (HAL_DMAEx_List_SetCircularMode(&List_GPDMA1_Channel0) != HAL_OK)
    {
      Error_Handler();
    }

    handle_GPDMA1_Channel0.Instance = GPDMA1_Channel0;
    handle_GPDMA1_Channel0.InitLinkedList.Priority = DMA_LOW_PRIORITY_LOW_WEIGHT;
    handle_GPDMA1_Channel0.InitLinkedList.LinkStepMode = DMA_LSM_FULL_EXECUTION;
    handle_GPDMA1_Channel0.InitLinkedList.LinkAllocatedPort = DMA_LINK_ALLOCATED_PORT0;
    handle_GPDMA1_Channel0.InitLinkedList.TransferEventMode = DMA_TCEM_BLOCK_TRANSFER;
    handle_GPDMA1_Channel0.InitLinkedList.LinkedListMode = DMA_LINKEDLIST_CIRCULAR;
    if (HAL_DMAEx_List_Init(&handle_GPDMA1_Channel0) != HAL_OK)
    {
      Error_Handler();
    }

    if (HAL_DMAEx_List_LinkQ(&handle_GPDMA1_Channel0, &List_GPDMA1_Channel0) != HAL_OK)
    {
      Error_Handler();
    }

    __HAL_LINKDMA(hsai, hdmarx, handle_GPDMA1_Channel0);
    }
}


void main(void)
{
[...]
  MX_GPDMA1_Init();
  MX_SAI1_Init();
  SystemIsolation_Config();

    /* set up GPDMA configuration */
  /* set GPDMA1 channel 0 used by SAI1 */
  if (HAL_DMA_ConfigChannelAttributes(&handle_GPDMA1_Channel0,DMA_CHANNEL_SEC|DMA_CHANNEL_PRIV|DMA_CHANNEL_SRC_SEC|DMA_CHANNEL_DEST_SEC)!= HAL_OK )
  {
    Error_Handler();
  }
[...]

  if (HAL_OK != HAL_SAI_Receive_DMA(&hsai_BlockB1, (uint8_t *) acquisition_buffer, N_BLOCK_SIZE))
  {
      Error_Handler();
  }

  printf("SAI1_B DMA configuration done.\n");

}
Any help or suggestions would be greatly appreciated as I'm a bit stuck on what to check next.
Best regards. 
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