STM32 Sending 12bit ADC over I2C

Question

How do I make sense of this STM32F4 data that's being sent over I2C? I'm sending this I2C stream from one STM32F4 to another STM32F4.

I'm getting the ACKs I expect, but the data itself looks a little unusual.

I have a 12bit ADC that I'm getting managed by a DMA. Here's the setup code:

  volatile uint32_t ADCValue[2];
 if(HAL_ADC_Start(&hadc1) != HAL_OK)
        HAL_GPIO_WritePin(GPIOC, LED3_Pin, SET);
 if(HAL_ADC_Start_DMA(&hadc1, (uint32_t*)ADCValue,4) != HAL_OK)
        HAL_GPIO_WritePin(GPIOC, LED4_Pin, SET);
 while(1){
 while(HAL_I2C_Master_Transmit(&hi2c3, 252, (uint8_t*) ADCValue[1], 4, 10000) != HAL_OK)
}

And, here's the ADC setup

ADC_HandleTypeDef hadc1;
DMA_HandleTypeDef hdma_adc1;

/* ADC1 init function */
void MX_ADC1_Init(void)
{
  ADC_ChannelConfTypeDef sConfig;

    /**Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion) 
    */
  hadc1.Instance = ADC1;
  hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV2;
  hadc1.Init.Resolution = ADC_RESOLUTION_8B;
  hadc1.Init.ScanConvMode = 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 = ENABLE;
  hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

    /**Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time. 
    */
  sConfig.Channel = ADC_CHANNEL_0;
  sConfig.Rank = 1;
  sConfig.SamplingTime = ADC_SAMPLETIME_144CYCLES;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

    /**Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time. 
    */
  sConfig.Channel = ADC_CHANNEL_1;
  sConfig.Rank = 2;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

}

So, naturally, the most ballsy thing I think I'm doing here is trying to break up a single ADCValue element into 4 8-bit values, since it's defined as a 32-bit int...

I'm getting 4 bytes after the address byte, but I'm not sure if this thing that I'm doing with the DMA and casting types is fundamentally flawed.

Any C experts got any insight on how to send 32-bit values over I2C with the HAL libraries?

JMA · Accepted Answer · 2018-01-11 08:05:31Z

0

I think that you are sending an invalid pointer to the I2C:

 while(HAL_I2C_Master_Transmit(&hi2c3, 252, (uint8_t*) ADCValue[1], 4, 10000) != HAL_OK)

I don't understand what do you want to send via I2C, this mean that the value of ADCValue[1] is a pointer to the data to transmit, maybe you should change by:

 while(HAL_I2C_Master_Transmit(&hi2c3, 252, (uint8_t*) ADCValue, 4, 10000) != HAL_OK)

If you want to send the value of ADCValue, or if you want to shift 1 byte:

 while(HAL_I2C_Master_Transmit(&hi2c3, 252, &((uint8_t*) ADCValue)[1], 4, 10000) != HAL_OK)

In this case it would be easier if you do an union between uin32 array and uint8 array.

answered Jan 11, 2018 at 8:05

JMA

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7 Comments

testname123 Over a year ago

Pointers confuse me...Thank you, I'll give this a go

JMA Over a year ago

Are you sure that this code is protected against benign races?

testname123 Over a year ago

What do you mean?

JMA Over a year ago

Imagine that I2C starts a transmision, when 2 bytes have been send, ADC ends the conversion and updates the value, then I2C transmit the other 2 bytes. The value transmited is half of the old value and half of the new value.

JMA Over a year ago

There are many solutions, If I2C transmision is faster than the ADC conversion you can use 2 variables and a pointer that points to the last value. When conversion ends change the pointer to the current value, start a new conversion with the other variable. I2C always works with the pointer to the last value.

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