Issues with GPS and WiFi Module Communication on Nucleo-H755ZI Board

[asha1114]

I've connected the Nucleo-H755ZI board to a GPS module (GY-GPS6MV2) via USART2 with a baud rate of 9600. The RX and TX pins are configured to PD5 and PD6, and I've enabled global interrupts to manage the incoming data. However, instead of receiving the expected NMEA sentences, I'm consistently getting a value of `-1.888836e-019`, which leads me to believe there might be an issue with the communication setup or data interpretation. Additionally, when I connected a WiFi module to the Nucleo-H755ZI using the same USART2 interface (on different occasions), the board consistently received the data `0x84`. Could you help me diagnose these issues and suggest what might be going wrong with the GPS and WiFi module connections?

/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body

  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include <string.h>
#include <stdio.h>
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */

#ifndef HSEM_ID_0
#define HSEM_ID_0 (0U) /* HW semaphore 0*/
#endif

/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/

UART_HandleTypeDef huart2;
DMA_HandleTypeDef hdma_usart2_rx;

/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
static void MX_GPIO_Init(void);
static void MX_DMA_Init(void);
static void MX_USART2_UART_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
uint8_t rxBuffer[128] = {0};
uint8_t rxIndex = 0;
uint8_t rxData;
float nmeaLong;
float nmeaLat;
float utcTime;
char northsouth;
char eastwest;
char posStatus;
float decimalLong;
float decimalLat;

float nmeaToDecimal(float coordinate) {
    int degree = (int)(coordinate/100);
    float minutes = coordinate - degree * 100;
    float decimalDegree = minutes / 60;
    float decimal = degree + decimalDegree;
    return decimal;
}

void gpsParse(char *strParse){
  if(!strncmp(strParse, "$GPGGA", 6)){
    sscanf(strParse, "$GPGGA,%f,%f,%c,%f,%c",
      &utcTime, &nmeaLat, &northsouth, &nmeaLong, &eastwest);
    decimalLat = nmeaToDecimal(nmeaLat);
    decimalLong = nmeaToDecimal(nmeaLong);
  }
  else if (!strncmp(strParse, "$GPGLL", 6)){
    sscanf(strParse, "$GPGLL,%f,%c,%f,%c,%f",
      &nmeaLat, &northsouth, &nmeaLong, &eastwest, &utcTime);
    decimalLat = nmeaToDecimal(nmeaLat);
    decimalLong = nmeaToDecimal(nmeaLong);
  }
  else if (!strncmp(strParse, "$GPRMC", 6)){
    sscanf(strParse, "$GPRMC,%f,%c,%f,%c,%f,%c",
      &utcTime, &posStatus, &nmeaLat, &northsouth, &nmeaLong, &eastwest);
    decimalLat = nmeaToDecimal(nmeaLat);
    decimalLong = nmeaToDecimal(nmeaLong);
  }
}

int gpsValidate(char *nmea){
    char check[3];
    char calculatedString[3];
    int index;
    int calculatedCheck;
    index=0;
    calculatedCheck=0;
    if(nmea[index] == '$')                 // Ensure that the string starts with a "$"
        index++;
    else
        return 0;
    while((nmea[index] != 0) && (nmea[index] != '*') && (index < 75)){      //No NULL reached, 75 char largest possible NMEA message, no '*' reached
        calculatedCheck ^= nmea[index];// calculate the checksum
        index++;
    }
    if(index >= 75){
        return 0;// the string is too long so return an error
    }
    if (nmea[index] == '*'){
        check[0] = nmea[index+1];    //put hex chars in check string
        check[1] = nmea[index+2];
        check[2] = 0;
    }
    else
        return 0;// no checksum separator found therefore invalid data
    sprintf(calculatedString,"%02X",calculatedCheck);
    return((calculatedString[0] == check[0])
        && (calculatedString[1] == check[1])) ? 1 : 0 ;
}
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
  if(huart->Instance==USART2){
    if(rxData!='\n' && rxIndex < sizeof(rxBuffer))              // if the character received is other than 'enter' ascii13, save the data in buffer
    {
      rxBuffer[rxIndex++]=rxData;
    }
    else
    {
      if(gpsValidate((char*) rxBuffer)) gpsParse((char*) rxBuffer);
      rxIndex=0;
      memset(rxBuffer,0,sizeof(rxBuffer));
    }
    HAL_UART_Receive_IT(&huart2,&rxData,1); // Enabling interrupt receive again
  }
}
/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

/* USER CODE BEGIN Boot_Mode_Sequence_1 */
  /*HW semaphore Clock enable*/
  __HAL_RCC_HSEM_CLK_ENABLE();
  /* Activate HSEM notification for Cortex-M4*/
  HAL_HSEM_ActivateNotification(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0));
  /*
  Domain D2 goes to STOP mode (Cortex-M4 in deep-sleep) waiting for Cortex-M7 to
  perform system initialization (system clock config, external memory configuration.. )
  */
  HAL_PWREx_ClearPendingEvent();
  HAL_PWREx_EnterSTOPMode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFE, PWR_D2_DOMAIN);
  /* Clear HSEM flag */
  __HAL_HSEM_CLEAR_FLAG(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0));

/* USER CODE END Boot_Mode_Sequence_1 */
  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_USART2_UART_Init();
  /* USER CODE BEGIN 2 */
  HAL_UART_Receive_IT(&huart2,&rxData,1);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}

/**
  * @brief USART2 Initialization Function
  * @PAram None
  * @retval None
  */
static void MX_USART2_UART_Init(void)
{

  /* USER CODE BEGIN USART2_Init 0 */

  /* USER CODE END USART2_Init 0 */

  /* USER CODE BEGIN USART2_Init 1 */

  /* USER CODE END USART2_Init 1 */
  huart2.Instance = USART2;
  huart2.Init.BaudRate = 9600;
  huart2.Init.WordLength = UART_WORDLENGTH_8B;
  huart2.Init.StopBits = UART_STOPBITS_1;
  huart2.Init.Parity = UART_PARITY_NONE;
  huart2.Init.Mode = UART_MODE_TX_RX;
  huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart2.Init.OverSampling = UART_OVERSAMPLING_16;
  huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart2.Init.ClockPrescaler = UART_PRESCALER_DIV1;
  huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart2) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetTxFifoThreshold(&huart2, UART_TXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetRxFifoThreshold(&huart2, UART_RXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_DisableFifoMode(&huart2) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART2_Init 2 */

  /* USER CODE END USART2_Init 2 */

}

/**
  * Enable DMA controller clock
  */
static void MX_DMA_Init(void)
{

  /* DMA controller clock enable */
  __HAL_RCC_DMA1_CLK_ENABLE();

  /* DMA interrupt init */
  /* DMA1_Stream0_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(DMA1_Stream0_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(DMA1_Stream0_IRQn);

}

/**
  * @brief GPIO Initialization Function
  * @PAram None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
/* USER CODE BEGIN MX_GPIO_Init_1 */
/* USER CODE END MX_GPIO_Init_1 */

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOD_CLK_ENABLE();

/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */
  __disable_irq();
  while (1)
  {
  }
  /* USER CODE END Error_Handler_Debug */
}

#ifdef  USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @PAram  file: pointer to the source file name
  * @PAram  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t *file, uint32_t line)
{
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

[Andrew Neil]

Different GPS module, but otherwise duplicate:

https://community.st.com/t5/stm32-mcus-embedded-software/data-form-neo-6m-gps-module/td-p/711701

You still haven't said what basic testing/debugging have you done on your interfaces with these external devices.

ie, are you actually receiving the raw NMEA text strings correctly - before doing your parsing & conversions.

Show your schematic.

Those Posting Tips again:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228