HAL_DCMI_FrameEventCallback is not called in dcmi snapshot mode

[eunoia]

I'm using an ov2640 camera.

When I use HAL_DCMI_Start_DMA(&hdcmi, DCMI_MODE_CONTINUOUS, (uint32_t)camBuf0, (CAM_W * CAM_H) / 2);, HAL_DCMI_FrameEventCallback is called,

but when I use HAL_DCMI_Start_DMA(&hdcmi, DCMI_MODE_SNAPSHOT, (uint32_t)camBuf0, (CAM_W * CAM_H) / 2);, HAL_DCMI_FrameEventCallback is never called. Why is this happening? Below are the relevant settings.

I'm using an STM32H743 MCU.

static void MX_DCMI_Init(void)
{

  /* USER CODE BEGIN DCMI_Init 0 */

  /* USER CODE END DCMI_Init 0 */

  /* USER CODE BEGIN DCMI_Init 1 */

  /* USER CODE END DCMI_Init 1 */
  hdcmi.Instance = DCMI;
  hdcmi.Init.SynchroMode = DCMI_SYNCHRO_HARDWARE;
  hdcmi.Init.PCKPolarity = DCMI_PCKPOLARITY_RISING;
  hdcmi.Init.VSPolarity = DCMI_VSPOLARITY_LOW;
  hdcmi.Init.HSPolarity = DCMI_HSPOLARITY_LOW;
  hdcmi.Init.CaptureRate = DCMI_CR_ALL_FRAME;
  hdcmi.Init.ExtendedDataMode = DCMI_EXTEND_DATA_8B;
  hdcmi.Init.JPEGMode = DCMI_JPEG_DISABLE;
  hdcmi.Init.ByteSelectMode = DCMI_BSM_ALL;
  hdcmi.Init.ByteSelectStart = DCMI_OEBS_ODD;
  hdcmi.Init.LineSelectMode = DCMI_LSM_ALL;
  hdcmi.Init.LineSelectStart = DCMI_OELS_ODD;
  if (HAL_DCMI_Init(&hdcmi) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN DCMI_Init 2 */

  /* USER CODE END DCMI_Init 2 */

}

void HAL_DCMI_MspInit(DCMI_HandleTypeDef* hdcmi)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  if(hdcmi->Instance==DCMI)
  {
  /* USER CODE BEGIN DCMI_MspInit 0 */

  /* USER CODE END DCMI_MspInit 0 */
    /* Peripheral clock enable */
    __HAL_RCC_DCMI_CLK_ENABLE();

    __HAL_RCC_GPIOE_CLK_ENABLE();
    __HAL_RCC_GPIOA_CLK_ENABLE();
    __HAL_RCC_GPIOC_CLK_ENABLE();
    __HAL_RCC_GPIOD_CLK_ENABLE();
    __HAL_RCC_GPIOG_CLK_ENABLE();
    __HAL_RCC_GPIOB_CLK_ENABLE();
    /**DCMI GPIO Configuration
    PE4     ------> DCMI_D4
    PE5     ------> DCMI_D6
    PE6     ------> DCMI_D7
    PA4     ------> DCMI_HSYNC
    PA6     ------> DCMI_PIXCLK
    PC6     ------> DCMI_D0
    PC7     ------> DCMI_D1
    PD3     ------> DCMI_D5
    PG10     ------> DCMI_D2
    PG11     ------> DCMI_D3
    PB7     ------> DCMI_VSYNC
    */
    GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOE, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_6;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_6|GPIO_PIN_7;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOD, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_10|GPIO_PIN_11;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);

    GPIO_InitStruct.Pin = GPIO_PIN_7;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF13_DCMI;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

    /* DCMI DMA Init */
    /* DCMI Init */
    hdma_dcmi.Instance = DMA1_Stream1;
    hdma_dcmi.Init.Request = DMA_REQUEST_DCMI;
    hdma_dcmi.Init.Direction = DMA_PERIPH_TO_MEMORY;
    hdma_dcmi.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_dcmi.Init.MemInc = DMA_MINC_ENABLE;
    hdma_dcmi.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;
    hdma_dcmi.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;
    hdma_dcmi.Init.Mode = DMA_CIRCULAR;
    hdma_dcmi.Init.Priority = DMA_PRIORITY_VERY_HIGH;
    hdma_dcmi.Init.FIFOMode = DMA_FIFOMODE_ENABLE;
    hdma_dcmi.Init.FIFOThreshold = DMA_FIFO_THRESHOLD_FULL;
    hdma_dcmi.Init.MemBurst = DMA_MBURST_SINGLE;
    hdma_dcmi.Init.PeriphBurst = DMA_PBURST_SINGLE;
    if (HAL_DMA_Init(&hdma_dcmi) != HAL_OK)
    {
      Error_Handler();
    }

    __HAL_LINKDMA(hdcmi,DMA_Handle,hdma_dcmi);

    /* DCMI interrupt Init */
    HAL_NVIC_SetPriority(DCMI_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(DCMI_IRQn);
  /* USER CODE BEGIN DCMI_MspInit 1 */

  /* USER CODE END DCMI_MspInit 1 */

  }

}