Sampling at 16KHz using ADC prescaler?

[RichardB01]

Hi, I need to sample the ADC at 16KHz to create an audio file. How can I do this using stm32duino?

Many thanks,
Richard

[fpistm]

Hi @Bambofy
on which board? Nucleo-L452RE-P?

ADC is limited on this core to analogRead() API which made a single conversion at a time. This is really not optimized and do not use all ADC capabilities.
You can try to play with ADC_SAMPLINGTIME and ADC_CLOCK_DIV which can be redefined thanks build_opt.h.

Arduino_Core_STM32/cores/arduino/stm32/analog.cpp

Line 57 in fd40374

#ifndef ADC_SAMPLINGTIME

Arduino_Core_STM32/cores/arduino/stm32/analog.cpp

Line 102 in fd40374

#ifndef ADC_CLOCK_DIV

Else use directly HAL/LL to play with ADC.

FYI, an issue is already opened to have an advanced ADC library with convenient API to use them #5

[RichardB01]

ok thank you

[RichardB01]

I'm trying to use the HAL api to set the prescaler of the ADC like this:

void setup()
{
  Serial.begin(9600);
  
  // put your setup code here, to run once:
  pinMode(CONFIG_MIC_PIN, INPUT);
  lastTick = millis();

  ADC_HandleTypeDef adcConfiguration;
  adcConfiguration.Instance = ADC1;
  adcConfiguration.Init.ClockPrescaler = ADC_CLOCKPRESCALER_PCLK_DIV1;
  adcConfiguration.Init.Resolution = ADC_RESOLUTION_8B;
  adcConfiguration.Init.DataAlign = ADC_DATAALIGN_LEFT;
  adcConfiguration.Init.ScanConvMode = DISABLE;
  adcConfiguration.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
  adcConfiguration.Init.LowPowerAutoWait = ENABLE;

  Serial.println(adcConfiguration.Init.ClockPrescaler);
  
  HAL_StatusTypeDef result = HAL_ADC_Init(&adcConfiguration);

  // 0 = ok
  // 1 = error
  // 2 = busy
  // 3 = timeout
  Serial.println(result); // returns 1
}

The status code returned is 1 (HAL_StatusTypeDef).

And it still samples at 9KHz? The analog pin is A0 / PA0?

[fpistm]

which board ?

[RichardB01]

which board ?

NUCLEO-L452RE-P

[fpistm]

and how you read value ?

[RichardB01]

and how you read value ?

void loop()
{
  byte sample = analogRead(CONFIG_MIC_PIN); // this should be 8 bits now.
 }

[fpistm]

Using analogRead call again the HAL_ADC_Init so your setup is simply ignore.

[RichardB01]

Ok is this setup ok? i'm not sure how to actually read the ADC now though:

#include "stm32l4xx_hal_adc.h"

const int CONFIG_MIC_PIN = PA0;

ADC_HandleTypeDef adcConfiguration;

void setup()
{
  Serial.begin(9600);
  
  // put your setup code here, to run once:
  pinMode(CONFIG_MIC_PIN, INPUT);

// adcConfiguration.Instance = ADC1;
//  adcConfiguration.Init.ClockPrescaler = ADC_CLOCKPRESCALER_PCLK_DIV1;
//  adcConfiguration.Init.Resolution = ADC_RESOLUTION_8B;
//  adcConfiguration.Init.DataAlign = ADC_DATAALIGN_LEFT;
//  adcConfiguration.Init.ScanConvMode = DISABLE;
//  adcConfiguration.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
//  adcConfiguration.Init.LowPowerAutoWait = ENABLE;
//  

  adcConfiguration.Init.ClockPrescaler = ADC_CLOCKPRESCALER_PCLK_DIV2;
  adcConfiguration.Init.Resolution = ADC_RESOLUTION_12B;
  adcConfiguration.Init.ScanConvMode = DISABLE;
  adcConfiguration.Init.ContinuousConvMode = ENABLE;
  adcConfiguration.Init.DiscontinuousConvMode = DISABLE;
  adcConfiguration.Init.NbrOfDiscConversion = 0;
  adcConfiguration.Init.ExternalTrigConv = ADC_EXTERNALTRIG_T1_CC1;
  adcConfiguration.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  adcConfiguration.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  adcConfiguration.Init.NbrOfConversion = 1;
  adcConfiguration.Init.DMAContinuousRequests = ENABLE;
  adcConfiguration.Init.EOCSelection = DISABLE;
    
  //Serial.println(adcConfiguration.Init.ClockPrescaler);
  
  HAL_StatusTypeDef result = HAL_ADC_Init(&adcConfiguration);

  HAL_ADC_Start(&adcConfiguration);

  // 0 = ok
  // 1 = error
  // 2 = busy
  // 3 = timeout
  Serial.println(result); // returns 1
}

void loop()
{
  //byte sample = analogRead(CONFIG_MIC_PIN); // this should be 8 bits now.
  if (HAL_ADC_PollForConversion(&adcConfiguration, 1000000) == HAL_OK)
  {
      uint32_t g_ADCValue = HAL_ADC_GetValue(&adcConfiguration);
      Serial.println(g_ADCValue);
  }
}

[RichardB01]

when i poll for conversion, it never receives HAL_OK

[RichardB01]

i guess i need to set up all the other pin information, see https://visualgdb.com/tutorials/arm/stm32/adc/

[fpistm]

Here an example:
https://github.com/STMicroelectronics/STM32CubeL4/blob/f6877af03b5c8b666b3443f5295cf95ec9c0b15d/Projects/NUCLEO-L452RE/Examples/ADC/ADC_RegularConversion_Polling/Src/main.c#L52

you have to call start and poll for conversion, I guess.
And also configure channel.

[fpistm]

Ah! Also call first analogRead(CONFIG_MIC_PIN) to init the g_current_pin then the HAL_ADC_MspInit
will enable the clock and properly init the pin.

So, in Setup():

void setup()
{
  Serial.begin(9600);
analogRead(CONFIG_MIC_PIN);
<your init code, do not use pinMode>

[RichardB01]

how do i find out what channel my analog pin is?