ADC timing issues when configured for multiple channel scanning.

[JimEno]

I'm trying to scan 6 channels at a 1 KHz rate. I used Timer 2 to generate 1 mSec trigger pulses for the ADC. I used the 'interrupt mode' to verify timing by pulsing an I/O port pin. I'll use DMA eventually. I setup the ISR to collect 24 samples and stop. I get 24 evenly spaced pulses (ADC conversions) at 1 mS intervals. I expected to get 4 bursts of 6 pulses (representing the 6-channel scan) with the burst spacing of 1 mS.

The Reference Manual says ALL 6 conversions should occur when triggered (I assume back to back), then the next 6 conversions would be made after the next Timer2 trigger pulse 1 mS later as follows:

|||||| |||||| |||||| ||||||

| 1 mS | 1 mS | 1 mS | = 1 KHz trigger rate

I included the Ref Manual statement below as well as my simple ISR routine. I thought the Timer 2 pulse was a 'sequence' trigger, not a 'conversion' trigger.

Where is my thinking wrong?

Reference Manual snippet:

18.4.13 Single conversion mode (CONT=0)

In Single conversion mode, the ADC performs once all the conversions of the channels. This mode is started with the CONT bit at 0 by either:

• Setting the ADSTART bit in the ADC_CR register (for a regular channel)

• Setting the JADSTART bit in the ADC_CR register (for an injected channel)

• External hardware trigger event (for a regular or injected channel) 

ADC ISR routine:

void ADC_SampleHandler(ADC_HandleTypeDef *hadc)

{

ADCResult = HAL_ADC_GetValue(hadc);

HAL_GPIO_WritePin(CS3_GPIO_Port, CS3_Pin, GPIO_PIN_SET);

for(k=0; k<500; k++);

HAL_GPIO_WritePin(CS3_GPIO_Port, CS3_Pin, GPIO_PIN_RESET);

if(++i == 24)

{

HAL_ADC_Stop_IT(&hadc1);

ADCdoneFlag = TRUE;

}

}

[FBL]

Hello @JimEno​,

Would you please specify the STM32 product you are using?

[JimEno]

I am using a Nucleo-L4A6ZG Evaluation Board and a custom daughter board (with an Arduino type interface). We will eventually port the code over to a fully custom board to support our final product.

[JimEno]

Also would like to add that I used the MX Code Generation tool to configure the ADC resource. It's a little lengthy, but here is the result:

/**

 * @brief ADC1 Initialization Function

 * @param None

 * @retval None

 */

static void MX_ADC1_Init(void)

{

 /* USER CODE BEGIN ADC1_Init 0 */

 /* USER CODE END ADC1_Init 0 */

 ADC_MultiModeTypeDef multimode = {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.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc1.Init.ScanConvMode = ADC_SCAN_ENABLE;

 hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

 hadc1.Init.LowPowerAutoWait = DISABLE;

 hadc1.Init.ContinuousConvMode = DISABLE;

 hadc1.Init.NbrOfConversion = 6;

 hadc1.Init.DiscontinuousConvMode = DISABLE;

 hadc1.Init.ExternalTrigConv = ADC_EXTERNALTRIG_T2_TRGO;

 hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;

 hadc1.Init.DMAContinuousRequests = DISABLE;

 hadc1.Init.Overrun = ADC_OVR_DATA_OVERWRITTEN;

 hadc1.Init.OversamplingMode = DISABLE;

 if (HAL_ADC_Init(&hadc1) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure the ADC multi-mode

 */

 multimode.Mode = ADC_MODE_INDEPENDENT;

 if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_4;

 sConfig.Rank = ADC_REGULAR_RANK_1;

 sConfig.SamplingTime = ADC_SAMPLETIME_2CYCLES_5;

 sConfig.SingleDiff = ADC_SINGLE_ENDED;

 sConfig.OffsetNumber = ADC_OFFSET_NONE;

 sConfig.Offset = 0;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_1;

 sConfig.Rank = ADC_REGULAR_RANK_2;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_2;

 sConfig.Rank = ADC_REGULAR_RANK_3;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_8;

 sConfig.Rank = ADC_REGULAR_RANK_4;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_13;

 sConfig.Rank = ADC_REGULAR_RANK_5;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /** Configure Regular Channel

 */

 sConfig.Channel = ADC_CHANNEL_14;

 sConfig.Rank = ADC_REGULAR_RANK_6;

 if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

 {

  Error_Handler();

 }

 /* USER CODE BEGIN ADC1_Init 2 */

 if (HAL_ADC_RegisterCallback(&hadc1, HAL_ADC_CONVERSION_COMPLETE_CB_ID, ADC_SampleHandler) != HAL_OK)

// if (HAL_ADC_RegisterCallback(&hadc1, HAL_ADC_CONVERSION_COMPLETE_CB_ID, ADC_FrameHandler) != HAL_OK)

 {

  Error_Handler();

 }

 /* USER CODE END ADC1_Init 2 */

}