STM32 ADC DMA Multi-Channel Readin using FreeRTOS and Timer 2

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1

Hey guys!
I’m trying to get an ADC reeading of 3 channels to work, i think i set up everything correctly but when i read my buffer, the data does not seem correct, not it works according to the Timer 2 timing of 1 second.

ADC config:
12 bits
Scan conversion enabled
Continuous conversion enabled
DMA Continuous requests enabled
Number of conversions = 3
The ranks are correct with cycles of 15
External trigger conversion source is set to Timer 2 Trigger Out Event

DMA:
ADC1
DMA2 Stream0
Peripheral to Memory
Low
Half Word
Circular

NVIC:
DMA2 stream0 global interrupt enabled by default

Timer:
64MHz cpu clock
PSC = 64k → 1kHz
ARR = 1k → 1s count

This is my Task 1:

void StartTask1(void const * argument)
{
  /* USER CODE BEGIN StartTask1 */
	HAL_ADC_Start_DMA(&hadc1, (uint32_t*) adcBuffer, ADC_CHANNEL_LENGTH);
	HAL_TIM_Base_Start(&htim2);
	//HAL_TIM_Base_Start_DMA(&htim8, (uint32_t*) adcBuffer, ADC_CHANNEL_LENGTH);

  /* Infinite loop */
  for(;;)
  {
	  HAL_GPIO_TogglePin(green_led_GPIO_Port, green_led_Pin);
	  // Check if DMA buffer is ready for processing
    osDelay(500);
  }
  /* USER CODE END StartTask1 */
}

The LED is just to test if the freeRTOS is working with the DMA (it may stop scheduling).
This is my buffer with a lenght of 100:

volatile uint16_t adcBuffer[ADC_CHANNEL_LENGTH];

And this is my CpltCallback:

void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)
{

	// Custom logic for ADC1 conversion completion
	adcThermistorValue = adcBuffer[0];
	adcAccelXValue = adcBuffer[1];
	adcAccelYValue = adcBuffer[2];
	dmaDataReadyFlag = 1;  // Set a flag to indicate that data is ready

}

Any ideas why this is not reading correctly, nor counting time correctly and reading with 1s intervals.

2

Are you able to get it working without FreeRTOS i.e. in a bare metal environment. If no, then it is likely not related to FreeRTOS and you should reach out to ST.

3

As aggarg says, the configuration of the ADC/DMA will have nothing to do with FreeRTOS, except how to signal the “done” event, so if the issue isn’t there, it is a STM issue, not a FreeRTOS one.

4

I resolved the issue (on a baremetal implementation), basically to use the Timer as an Event source, you need to disable the Continuous Conversion on the ADC. It worked for me on my NUCLEO-F767ZI.
But thanks for the response anyway.

5

Glad that you resolved it. Does it work with FreeRTOS also or are you still facing problem with that?

1 Like
7

Yes, i just did the same implementation there and it works. Probably i will have problems if i have faster readings with the freeRTOS scheduler, but i can just increase the size of the ADC DMA buffer.
As i said before, if you have Continuous connversion mode it will operate at the clock prescaler frequency. Deactivate that and it will read when the timer generates an event.

8

Thank you for sharing your solution!