What is the accuracy of the ADC watchdog [STM32F303]?

I could now improve my measurements a tiny bit. As i did forget about my signal i used, there were some artifacts (valleys and mountains in the signal). Those came from the DAC that was generating the signal.

But still the values when the watchdog fires are not precise. My test setup is on a breadboard. The increasing numbers to the right are, because the signal curve flattens at higher level, and produces more measured values. The signal is a 2Hz triangular (somewhat) waveform.

The watchdog is digital, so its accuracy is the same as any ADC readout.

I don't know how do you determine the value in the interrupt, but if the latency is too high and you have continuous conversions, you may read out not the value which triggered the interrupt, but value from some subsequent conversion.

JW

I have now checked on the preserve option in particular. It works as expected. But the watchdog is still not working as it should. I have read in the manual:

The watchdog comparison is performed on the raw converted data before any alignment calculation and before applying any offsets (the data which is compared is not signed).

When it says "Data", there should be no watchdog interrupt that has a value of between 3000 and 3200.

This is the code currently used:

static void MX_ADC1_Init(void)
{
 
 /* USER CODE BEGIN ADC1_Init 0 */
 
 /* USER CODE END ADC1_Init 0 */
 
 ADC_MultiModeTypeDef multimode = {0};
 ADC_AnalogWDGConfTypeDef AnalogWDGConfig = {0};
 ADC_ChannelConfTypeDef sConfig = {0};
 
 /* USER CODE BEGIN ADC1_Init 1 */
 
 /* USER CODE END ADC1_Init 1 */
 
 /** Common config
 */
 hadc1.Instance = ADC1;
 hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
 hadc1.Init.Resolution = ADC_RESOLUTION_12B;
 hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
 hadc1.Init.ContinuousConvMode = ENABLE;
 hadc1.Init.DiscontinuousConvMode = DISABLE;
 hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
 hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
 hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
 hadc1.Init.NbrOfConversion = 1;
 hadc1.Init.DMAContinuousRequests = ENABLE;
 hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
 hadc1.Init.LowPowerAutoWait = DISABLE;
 hadc1.Init.Overrun = ADC_OVR_DATA_OVERWRITTEN;
 if (HAL_ADC_Init(&hadc1) != HAL_OK)
 {
 Error_Handler();
 }
 
 /** B_Configure the ADC multi-mode
 */
 multimode.Mode = ADC_MODE_INDEPENDENT;
 if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)
 {
 Error_Handler();
 }
 
 /** Configure Analog WatchDog 1
 */
 AnalogWDGConfig.WatchdogNumber = ADC_ANALOGWATCHDOG_1;
 AnalogWDGConfig.WatchdogMode = ADC_ANALOGWATCHDOG_SINGLE_REG;
 AnalogWDGConfig.HighThreshold = 3200;
 AnalogWDGConfig.LowThreshold = 3000;
 AnalogWDGConfig.Channel = ADC_CHANNEL_1;
 AnalogWDGConfig.ITMode = ENABLE;
 if (HAL_ADC_AnalogWDGConfig(&hadc1, &AnalogWDGConfig) != HAL_OK)
 {
 Error_Handler();
 }
 
 /** Configure Regular Channel
 */
 sConfig.Channel = ADC_CHANNEL_1;
 sConfig.Rank = ADC_REGULAR_RANK_1;
 sConfig.SingleDiff = ADC_SINGLE_ENDED;
 sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
 sConfig.OffsetNumber = ADC_OFFSET_NONE;
 sConfig.Offset = 0;
 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
 {
 Error_Handler();
 }
}

void HAL_ADC_LevelOutOfWindowCallback(struct __ADC_HandleTypeDef* hadc){
//create delay
	for(int i = 0; i < 100; i++){
		if(lastStart < 0){
			print("WTF",3);
		}
	}
 
	uint32_t value = hadc->Instance->DR;
 
	if(value >= 2900 && value < 3300){
		BSP_LED_Toggle(LED3);
		outLevelCount[value-2900]++;
	}
 
	if(HAL_GetTick() - lastStart > 30000){
		HAL_ADC_Stop_IT(&hadc1);
	}
}

> No, i have set the option to preserve the data in the register.

That has nothing to do with the watchdog. That setting means, that in case of overflow (i.e. if new conversion finishes and previous conversion's data have not been read) the new conversion's data are not thrown away, but replace the old data.

You not only don't read the value which caused the interrupt, by adding deliberate delay in the ISR you more-less make sure you read an entirely different data, converted much later than the data which caused the interrupt.

JW

> When i read the register, it should be the value from what the watchdog triggered as i understand.

No. Why would it be? Where do you see this written?

> And with preserving the data i would make sure, i dont get other values written into it before i have read them.

No. As I've said, that option has nothing to do with watchdog.

There's no such functionality as "preserve converted value which triggered the watchdog" in the ADC.

JW

I just found out, that the ADC watchdog only works as expected, when the adc runs at 2Mhz or lower! It may work slightly above that... i havent tried.