STM32F767 internal temperature reading issues

[PG29]

Hello, 

I'm trying to measure cyclic temperature on a dedicated task with FreeRTOS. For that, I set my ADC with DMA, based on the example provided here (at DMA section: https://wiki.st.com/stm32mcu/wiki/Getting_started_with_ADC#Configure_DMA) 

For now, my task is as follows

#define T1 30.0
#define T2 110.0

/*....*/
/*Some other stuff*/
/*....*/

void StartSurvTemp(void const * argument)
{
  /* USER CODE BEGIN StartSurvTemp */
  float cal_temp1 = (float) *(volatile uint16_t*) 0x1FF0F44C; //Cal temp 1
  float cal_temp2 = (float) *(volatile uint16_t*) 0x1FF0F44E; //Cal temp 2
  char buffer[50];
  float temperature = 0.0;

  HAL_ADC_Start_DMA(&hadc1, (uint32_t *)&raw_temp, 1);
  /* Infinite loop */
  for(;;)
  {

	    temperature = T1 + (T2 - T1) * (raw_temp - cal_temp1) / (cal_temp2 - cal_temp1);
		sprintf(buffer, "Raw temp : %lu, Computed temp (Celsius) : %.4f\r\n", raw_temp, temperature);
		HAL_UART_Transmit(&huart3, buffer, strlen(buffer), 10);
		osDelay(1000);
  }
  /* USER CODE END StartSurvTemp */
}

I have two major issues with this code. 

First, when it's the first run of the code, I have strange calculated values, and it's solved with a press on the reset key

Raw temp : 939, Computed temp (Celsius) : 37090607759360.0000
Raw temp : 943, Computed temp (Celsius) : 7212297728.0000
Raw temp : 943, Computed temp (Celsius) : 6908214272.0000
Raw temp : 946, Computed temp (Celsius) : 7679472828416.0000
Raw temp : 947, Computed temp (Celsius) : 1783121280.0000
<<board reset>>
Raw temp : 947, Computed temp (Celsius) : 29.3626
Raw temp : 945, Computed temp (Celsius) : 30.2532
Raw temp : 946, Computed temp (Celsius) : 30.1688
Raw temp : 948, Computed temp (Celsius) : 30.0001
Raw temp : 949, Computed temp (Celsius) : 29.9157

The second one is about the value itself, Indeed, I tried to freeze the board with a freeze spray, and the temperature grew.

Raw temp : 910, Computed temp (Celsius) : 33.2068
Raw temp : 917, Computed temp (Celsius) : 32.6161
Raw temp : 921, Computed temp (Celsius) : 32.2785
<<Freeze spray>>
Raw temp : 853, Computed temp (Celsius) : 38.0169
Raw temp : 838, Computed temp (Celsius) : 39.2827
Raw temp : 840, Computed temp (Celsius) : 39.1140

Do you have any idea? 

Thanks in advance 

[mƎALLEm]

Hello,

Do you have the same behaviours without RTOS?

[PG29]

Hello, 

Yes, same behaviours without RTOS. 

[mƎALLEm]

So if the behavior is reproduced without RTOS, I suppose there is no reason to talk about RTOS.

keep the discussion focused on the temperature reading.

This thread will be moved to STM32 MCU products forum board.