Please help me determine the ADC sampling frequency

[mravenca]

Hello,

I would like to determine the ADC sampling frequency.

I am initializing the ADC with following:

hadc1.Instance = ADC1;

hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;

hadc1.Init.Resolution = ADC_RESOLUTION_12B;

hadc1.Init.ScanConvMode = ADC_SCAN_ENABLE;

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 = 2;

hadc1.Init.DMAContinuousRequests = DISABLE;

hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;

if (HAL_ADC_Init(&hadc1) != HAL_OK)

{

Error_Handler();

}

/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.

*/

sConfig.Channel = ADC_CHANNEL_0;

sConfig.Rank = ADC_REGULAR_RANK_1;

sConfig.SamplingTime = ADC_SAMPLETIME_112CYCLES;//ADC_SAMPLETIME_3CYCLES;

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

{

Error_Handler();

}

/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.

*/

sConfig.Channel = ADC_CHANNEL_1;

sConfig.Rank = ADC_REGULAR_RANK_2;

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

{

Error_Handler();

Here is a content of my SystemClock_Config:

RCC_OscInitTypeDef RCC_OscInitStruct = {0};

RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

/** Configure the main internal regulator output voltage

*/

__HAL_RCC_PWR_CLK_ENABLE();

__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

/** Initializes the RCC Oscillators according to the specified parameters

* in the RCC_OscInitTypeDef structure.

*/

RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;

RCC_OscInitStruct.HSIState = RCC_HSI_ON;

RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;

RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;

RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;

RCC_OscInitStruct.PLL.PLLM = 8;

RCC_OscInitStruct.PLL.PLLN = 128;

RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;

RCC_OscInitStruct.PLL.PLLQ = 2;

RCC_OscInitStruct.PLL.PLLR = 2;

if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)

{

Error_Handler();

}

/** Initializes the CPU, AHB and APB buses clocks

*/

RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK

|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;

RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;

RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV2;

RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;

RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)

{

Error_Handler();

}

How do I determine (or eventually set following my desire) the ADC sampling frequency? I believe it's done with "sConfig.SamplingTime = ADC_SAMPLETIME_112CYCLES;". How long is one cycle in my setup?

Thank you very much!

Vaclav

[AScha.3]

Hi,

the ADC is on AHB bus , you set to xx? MHz . + divide by 4 .

ADC needs 12 clks + sampling time, you set to ??? ; on rank ? , you set to have 2 conversions.

So conversion speed is 12+sampling clocks at the ahb-bus/4 clock.

[mravenca]

Can you please check my clock setup and tell me the ADC Sampling Frequency?

Here is the clock setup:

As I wrote before, I am setting sConfig.SamplingTime = ADC_SAMPLETIME_112CYCLES.

Thank you very much!

Vaclav

[AScha.3 · Accepted solution]

So AHB is at 64M now; divider 4 -> 16M ; = 62,5ns

adc sampl. 112 + 12 (12 bit resolution) -> 124 cyc.

16M / 124 = 129 kHz , sampling.

+

I always check real rate, its so easy to calculate wrong. 🙂

Simple check: make a loop with adc conversions and set /reset a port pin, maybe a LED is on a pin you can use.

Then look with scope, is it about the right timing.(if using HAL calls, they might need extra 1..2us , so just do a loop with 1000 conversions , should need about 8 ms . )

Or make longer loop, 10000 conversions, and check with reading  HAL_GetTick(); and see time in ms steps; about 80 ms then.

[mravenca]

Thank you very much AScha.3!