What is missing to make stm32 ADC DMA work? Transfer Compete does not occur

Question

I am using a stm32f3 discovery board and the HAL from CubeMX. I am trying to use 2 ADC channels at ADC4. I configured DMA in circular mode. Befor the main loop in main, I call:

HAL_ADC_Start_DMA(&hadc4, DMA_adc4_buffer, 16);

I implemented the functions HAL_ADC_ConvHalfCpltCallback and HAL_ADC_ConvCpltCallback. Now the strange part: HAL_ADC_ConvHalfCpltCallback is called regularly, HAL_ADC_ConvCpltCallback is NOT.

It tells me, that the ADC with DMA transfer is running fine. But why is transfer compete callback not called? If I start the ADC with HAL_ADC_Start_IT the interrupt function is called, but that is not what I want.

Putting breakpoints in HAL_DMA_IRQHandlerin the ST HAL also shows, that the callback is never called.

For completeness here parts of the ADC4_Init function:

/**Common config 
*/
hadc4.Instance = ADC4;
hadc4.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
hadc4.Init.Resolution = ADC_RESOLUTION_12B;
hadc4.Init.ScanConvMode = ADC_SCAN_ENABLE;
hadc4.Init.ContinuousConvMode = ENABLE;
hadc4.Init.DiscontinuousConvMode = DISABLE;
hadc4.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
hadc4.Init.ExternalTrigConv = ADC_SOFTWARE_START;
hadc4.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc4.Init.NbrOfConversion = 2;
hadc4.Init.DMAContinuousRequests = ENABLE;
hadc4.Init.EOCSelection = ADC_EOC_SEQ_CONV;
hadc4.Init.LowPowerAutoWait = DISABLE;
hadc4.Init.Overrun = ADC_OVR_DATA_OVERWRITTEN;

Thank your for ideas.

Answer 1

The problem was that the clock of the ADC was 48 MHz, the core clock only 12 MHz. The function HAL_DMA_IRQHandler checks frst for the interrupt flag for half transfer complete, then for transfer complete in the style

if (half transfer complete){
  HAL_ADC_ConvHalfCpltCallback();
} **ELSE** if (transfer complete){
  HAL_ADC_ConvCpltCallback();
}

Since half transfer interrupt flag is always set so fast by the ADC / DMA and the processor is so slow, the core never comes to the seconds ìfbranch and thus never calls the ConvCpltCallback().