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ADC in Dual Mode Simultaneously

paul-henri
Associate II
Posted on July 22, 2013 at 15:27

Hi everyones,

I am stuying the example from STM32 libraries (ADC_DualModeRegulSimu). I understand how the whole program works but I need some information and I have few questions about this code confronting to my project.

First of all, I need to convert 2 analog values simultaneously because I plan to compute a phase correlation (that's why I need the simultaneously conversion).

In the code, the converted value are put in a word of length 32 bits : 

extern __IO uint16_t aADCDualConvertedValue[2];

I want to stock the first and second value (half-word) in two vector that I have defined. I first decided to create a while statement like this :

while(counter<Max && ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC && ADC_GetFlagStatus(ADC2, ADC_FLAG_EOC)) {

vector1[counter] = aADCDualConvertedValue[0];

vector2[counter] = aADCDualConvertedValue[1];

counter++;

}

But, this method seems to be unsafe because, we can't be certain that aADCDualConvertedValue[0] and aADCDualConvertedValue[1] are sampled at the same time owing to the number of cycles taken by while conditions.

So, what's the best way to stock the simultaneously data safely ?

Another problem, the conversion starts like this (after initializing the two ADC) :

ADC_SoftwareStartConv(ADC1);

 

ADC_SoftwareStartConv(ADC2);

 

Does-it mean that ADC2 starts to convert one cycle after ADC1, thus first both samples are not converted simultaneously ?

Thks.

#adc #stm32
23 REPLIES 23
Posted on July 22, 2013 at 17:22

If it is using DMA, I'm not sure of the merit of waiting on EOC. The two ADC are in lock-step, so EOC on one will infer EOC on the other.

The DMA implementation reads a single 32-bit word containing both samples from the ADC, and writes that to an output array.

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paul-henri
Associate II
Posted on July 23, 2013 at 08:44

So, to you, I just need to wait on EOC of one ADC to acquire a new sample ?

And what about the starting of both ADC, how start the both simultaneously (in reference to my second question).

Thks.

paul-henri
Associate II
Posted on July 23, 2013 at 11:34

I have many problems to have my ADC work.

Please, have a look on my code :

main :

/////////////////////////////////////////

 

// ADC configuration

 

/////////////////////////////////////////

 

 

 

ADC_CommonInitTypeDef ADC_CommonInitStructure;

 

// peripheral clocks

 

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);

 

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);

 

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);

 

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC2, ENABLE);

 

 

 

DMA_InitTypeDef DMA_InitStructure;

 

DMA_Config(&DMA_InitStructure);

 

GPIO_Config();

 

 

 

// common init for ADC

 

ADC_CommonInitStructure.ADC_Mode = ADC_DualMode_RegSimult;

 

ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;

 

ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_1;

 

ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_20Cycles;

 

ADC_CommonInit(&ADC_CommonInitStructure);

 

 

 

// ADC1

 

ADC1_CH10_Config();

 

// ADC2

 

ADC2_CH11_Config();

 

 

 

// DMA can transfer DATA after sampling

 

ADC_MultiModeDMARequestAfterLastTransferCmd(ENABLE);

 

ADC_Cmd(ADC1, ENABLE);

 

ADC_Cmd(ADC2, ENABLE);

 

 

 

// starting the conversion

 

ADC_SoftwareStartConv(ADC1);

 

ADC_SoftwareStartConv(ADC2);

 

 

 

/////////////////////////////////////////

 

// main loop

 

/////////////////////////////////////////

 

    while(1)

 

    {

 

    /////////////////////////////////////////

 

    // acquire data && windowing the signal

 

    /////////////////////////////////////////

 

    // MAXLEN data

 

    while(k<MAXLEN){

 

    while(DMA_GetITStatus(DMA2_Stream0,DMA_IT_HTIF0)==RESET){

 

    // SIGNAL : conversion is occurring

 

    LEDOn(LED4);

 

    }

 

    // END of Conversion

 

    // take data

 

    i=1;

 

    k++;

 

    }

 

    // SIGNAL : end of global conversion

 

LEDOff(LED4);

 

// SIGNAL : start the signal analysis

 

LEDOn(LED3);

 

    k=0;

 

    i=0;

 

}

ADC 1 Config :

void ADC1_CH10_Config(void)

 

{

 

  /* defined values in stm32f4xx_adc.h  and main.h */

 

  ADC_InitTypeDef ADC_InitStructure;

 

  ADC_InitStructure.ADC_Resolution = ADC_Resolution_8b;

 

  ADC_InitStructure.ADC_ScanConvMode = ENABLE;

 

  ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;

 

  ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;

 

  ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;

 

  ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;

 

  ADC_InitStructure.ADC_NbrOfConversion = 1;

 

  ADC_Init(ADC1, &ADC_InitStructure);

 

 

 

  /* ADC1 regular channels 11 configuration */

 

  ADC_RegularChannelConfig(ADC1, ADC_Channel_10, 1, ADC_SampleTime_112Cycles);

 

}

 

ADC 2 config :

void ADC2_CH11_Config(void)

 

{

 

  /* defined values in stm32f4xx_adc.h  and main.h */

 

  ADC_InitTypeDef ADC_InitStructure;

 

  ADC_InitStructure.ADC_Resolution = ADC_Resolution_8b;

 

  ADC_InitStructure.ADC_ScanConvMode = ENABLE;

 

  ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;

 

  ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;

 

  ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;

 

  ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;

 

  ADC_InitStructure.ADC_NbrOfConversion = 1;

 

  ADC_Init(ADC2, &ADC_InitStructure);

 

 

 

  /* ADC2 regular channels 12 configuration */

 

  ADC_RegularChannelConfig(ADC2, ADC_Channel_12, 1, ADC_SampleTime_112Cycles);

 

}

 

DMA config : 

void DMA_Config(DMA_InitTypeDef* DMA_InitStructure)

 

{

 

  /* defined values in stm32f4xx_dma.h  and main.h */

 

  DMA_InitStructure->DMA_Channel = DMA_Channel_0;

 

  DMA_InitStructure->DMA_Memory0BaseAddr = (uint32_t)&aADCDualConvertedValue;

 

  DMA_InitStructure->DMA_PeripheralBaseAddr = (uint32_t)ADC_CCR_ADDRESS;

 

  DMA_InitStructure->DMA_DIR = DMA_DIR_PeripheralToMemory;

 

  DMA_InitStructure->DMA_BufferSize = 2;

 

  DMA_InitStructure->DMA_PeripheralInc = DMA_PeripheralInc_Disable;

 

  DMA_InitStructure->DMA_MemoryInc = DMA_MemoryInc_Enable;

 

  DMA_InitStructure->DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;

 

  DMA_InitStructure->DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;

 

  DMA_InitStructure->DMA_Mode = DMA_Mode_Circular;

 

  DMA_InitStructure->DMA_Priority = DMA_Priority_High;

 

  DMA_InitStructure->DMA_FIFOMode = DMA_FIFOMode_Enable;

 

  DMA_InitStructure->DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;

 

  DMA_InitStructure->DMA_MemoryBurst = DMA_MemoryBurst_Single;

 

  DMA_InitStructure->DMA_PeripheralBurst = DMA_PeripheralBurst_Single;

 

  DMA_Init(DMA2_Stream0, DMA_InitStructure);

 

  /* DMA2_Stream0 enable */

 

  DMA_Cmd(DMA2_Stream0, ENABLE);

 

}

 

GPIO config :

void GPIO_Config(void)

 

{

 

  /* defined values in stm32f4xx_gpio.h  and main.h */

 

  GPIO_InitTypeDef GPIO_InitStructure;

 

  /* ADC Channel 10 -> PC0

 

     ADC Channel 11 -> PC1

 

     ADC Channel 12 -> PC2

 

  */

 

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1 | GPIO_Pin_2;

 

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;

 

  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;

 

  GPIO_Init(GPIOC, &GPIO_InitStructure);

 

}

I test DMA_GetITStatus(DMA2_Stream0,DMA_IT_HTIF0)==RESET and ADC_GetFlagStatus and DMA_GetFlagStatus but none works. Either I have an infinite loop, either I have my LED blinking but if I change the prescaler for example, sample time don't change...

More over, I discover that ADC 1 and ADC 2 doesn't take the same duration to convert...

I am a bit confused with this ADC configuration. I need some advices on this.

Thks.

Posted on July 23, 2013 at 16:47

There seem to be some inconsistencies in the channel selections, I don't think you want to be scan converting with a single channel per ADC (scan implies you have more than one). I personally prefer to pace ADC conversions with a timer rather than jam them back-to-back. This way the sample rate in unambiguous. Check also the rated speed of the ADC, the CPU should perhaps be running at 144 MHz, not 168 MHz

I suspect the HT (half-transfer) of a 2 16-bit word buffer churns at an excessive rate. I would make the buffer bigger, for HT to make any sense you'd want at least 4 16-bit words to how two pairs of samples. This is how I'd attack a dual channel acquisition.

// STM32 ADC IQ Sample @ 200 KHz (PC.1, PC.2) STM32F4 Discovery - sourcer32@gmail.com
// Assumptions per system_stm32f4xx.c CPU @ 168 MHz, APB2 @ 84 MHz (/2), APB1 @ 42 MHz (/4)
#include ''stm32f4_discovery.h''
/**************************************************************************************/
void RCC_Configuration(void)
{
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC2, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
}
/**************************************************************************************/
void GPIO_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* ADC Channel 11 -> PC1
ADC Channel 12 -> PC2
*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1 | GPIO_Pin_2;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;
GPIO_Init(GPIOC, &GPIO_InitStructure);
}
/**************************************************************************************/
void ADC_Configuration(void)
{
ADC_CommonInitTypeDef ADC_CommonInitStructure;
ADC_InitTypeDef ADC_InitStructure;
/* ADC Common Init */
ADC_CommonInitStructure.ADC_Mode = ADC_DualMode_RegSimult;
ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;
ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_1; // 2 half-words one by one, 1 then 2
ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_5Cycles;
ADC_CommonInit(&ADC_CommonInitStructure);
ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;
ADC_InitStructure.ADC_ScanConvMode = DISABLE; // 1 Channel
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE; // Conversions Triggered
ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_Rising;
ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T2_TRGO;
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
ADC_InitStructure.ADC_NbrOfConversion = 1;
ADC_Init(ADC1, &ADC_InitStructure);
ADC_Init(ADC2, &ADC_InitStructure); // Mirror on ADC2
/* ADC1 regular channel 11 configuration */
ADC_RegularChannelConfig(ADC1, ADC_Channel_11, 1, ADC_SampleTime_15Cycles); // PC1
/* ADC2 regular channel 12 configuration */
ADC_RegularChannelConfig(ADC2, ADC_Channel_12, 1, ADC_SampleTime_15Cycles); // PC2
/* Enable DMA request after last transfer (Multi-ADC mode) */
ADC_MultiModeDMARequestAfterLastTransferCmd(ENABLE);
/* Enable ADC1 */
ADC_Cmd(ADC1, ENABLE);
/* Enable ADC2 */
ADC_Cmd(ADC2, ENABLE);
}
/**************************************************************************************/
#define BUFFERSIZE 800 // I+Q 200KHz x2 HT/TC at 1KHz
__IO uint16_t ADCDualConvertedValues[BUFFERSIZE]; // Filled as pairs ADC1, ADC2
static void DMA_Configuration(void)
{
DMA_InitTypeDef DMA_InitStructure;
DMA_InitStructure.DMA_Channel = DMA_Channel_0;
DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&ADCDualConvertedValues[0];
DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)0x40012308; // CDR_ADDRESS; Packed ADC1, ADC2
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
DMA_InitStructure.DMA_BufferSize = BUFFERSIZE; // Count of 16-bit words
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Enable;
DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
DMA_Init(DMA2_Stream0, &DMA_InitStructure);
/* Enable DMA Stream Half / Transfer Complete interrupt */
DMA_ITConfig(DMA2_Stream0, DMA_IT_TC | DMA_IT_HT, ENABLE);
/* DMA2_Stream0 enable */
DMA_Cmd(DMA2_Stream0, ENABLE);
}
/**************************************************************************************/
void TIM2_Configuration(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
/* Time base configuration */
TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
TIM_TimeBaseStructure.TIM_Period = (84000000 / 200000) - 1; // 200 KHz, from 84 MHz TIM2CLK (ie APB1 = HCLK/4, TIM2CLK = HCLK/2)
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
/* TIM2 TRGO selection */
TIM_SelectOutputTrigger(TIM2, TIM_TRGOSource_Update); // ADC_ExternalTrigConv_T2_TRGO
/* TIM2 enable counter */
TIM_Cmd(TIM2, ENABLE);
}
/**************************************************************************************/
void NVIC_Configuration(void)
{
NVIC_InitTypeDef NVIC_InitStructure;
/* Enable the DMA Stream IRQ Channel */
NVIC_InitStructure.NVIC_IRQChannel = DMA2_Stream0_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
}
/**************************************************************************************/
void DMA2_Stream0_IRQHandler(void) // Called at 1 KHz for 200 KHz sample rate, LED Toggles at 500 Hz
{
/* Test on DMA Stream Half Transfer interrupt */
if(DMA_GetITStatus(DMA2_Stream0, DMA_IT_HTIF0))
{
/* Clear DMA Stream Half Transfer interrupt pending bit */
DMA_ClearITPendingBit(DMA2_Stream0, DMA_IT_HTIF0);
/* Turn LED3 off: Half Transfer */
STM_EVAL_LEDOff(LED3);
// Add code here to process first half of buffer (ping)
}
/* Test on DMA Stream Transfer Complete interrupt */
if(DMA_GetITStatus(DMA2_Stream0, DMA_IT_TCIF0))
{
/* Clear DMA Stream Transfer Complete interrupt pending bit */
DMA_ClearITPendingBit(DMA2_Stream0, DMA_IT_TCIF0);
/* Turn LED3 on: End of Transfer */
STM_EVAL_LEDOn(LED3);
// Add code here to process second half of buffer (pong)
}
}
/**************************************************************************************/
int main(void)
{
RCC_Configuration();
GPIO_Configuration();
NVIC_Configuration();
TIM2_Configuration();
DMA_Configuration();
ADC_Configuration();
STM_EVAL_LEDInit(LED3); /* Configure LEDs to monitor program status */
STM_EVAL_LEDOn(LED3); /* Turn LED3 on, 500 Hz means it working */
/* Start ADC1 Software Conversion */
ADC_SoftwareStartConv(ADC1);
while(1); // Don't want to exit
}

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paul-henri
Associate II
Posted on July 25, 2013 at 11:40

Why on the first way the sample rate would be ambiguous ? We fix the prescaler, the time delay between two conversion... It seems sure.

About your code, ok the timer send trigger with a frequency of 200 khz. But I don't understand why the DMA IRQ Handler is called with a frequency of 1Khz...

To fill table of BUFFERSIZE length, it takes 400*TimeOfConversion, here it seems to be at a frequency higher than 1 kHz...

Thks.

paul-henri
Associate II
Posted on July 27, 2013 at 13:57

Up !

Thks.

Posted on July 27, 2013 at 17:55

Don't badger, I'm not on staff.

It's the weekend, I don't have a scope to hand. Unless I messed up the timer settings, and math, the 200 sample pairs at 200000 KHz will occur 1000 times a second, ie 1 KHz

Ambiguous, perhaps there is a more elegant term. I don't spend a lot of time working with ADCs, I do however believe that the start time of the conversion in the time domain is critical, the completion time of the conversion less so. While there can be a case for saturating the ADC and be tied to sample times, and dwell times, I find it clearer to have a hard timebase to disciplining the ADC against that. I want to change the rate, I change one timer setting, and don't have to play games with ADC internal behaviours. It's also possible to advance/retard the timer in a very controlled fashion.
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paul-henri
Associate II
Posted on July 30, 2013 at 10:57

Hi,

Thanks for all you explanation.

Obviously, I am confronted to a new problem : I test the output ADC's values. I send to PC2 an signal between 0 and 1 volt -don't consider impedance issue, and it is not a sampling frequency issue- I check the voltage value on PC2 with a voltmeter.

I look converted values with STMStudio for example, but I obtain funky values (It seems to be random values)...

Let's have a look of this :

0690X00000604oLQAQ.png

I don't understand why whereas my circuit seems well done, and I don't forget to link the GND pin...  The only 

What can be the cause of such a problem with the ADC's converted values ?

Thks.

Posted on July 30, 2013 at 17:40

I don't know how you are generating the 8-bit value you are watching. If you are getting a lot of variability you could increase the ADC's sample time cycles.

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