1
\$\begingroup\$

I'm using an ST-Link broken off from a NUCLEO board to program a custom board with an STM32G4A1 on it. The issue is that UART transmission only seems to work while the ST-Link is connected (verified with an oscilloscope). This is especially confusing since the LED blinks in the while loop are still working, indicating that the program is actually running.

I've used this ST-Link with several custom boards at this point, and never had an issue like this. Any idea as to what might be causing this?

Additional Details

The USART1_TX on the board connects to nothing apart from the RX pin on the ST-Link. The ST-Link SWD pins and UART pins are connected to the board using a Wurth SKEDD connector - when disconnecting, this is the connector that is removed.

When the ST-Link is connected, I can read data from UART_TX using the serial monitor and see the UART activity on the pin using the scope. When I disconnect the ST-Link, the serial monitor stops (obviously expected) and there is no more UART activity on the pin (not expected).

Power comes from a benchtop power supply set to 9V (there's an LDO on the board giving 3V3). The scope is an Analog Discovery 2, with the positive input connected to USART1_TX and the negative connected to the power supply negative.

Code

The main.c code is as follows:

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2024 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "stdlib.h"
#include "string.h"
/* USER CODE END Includes */

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

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
//#define RX
/* USER CODE END PD */

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

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
TIM_HandleTypeDef htim2;

UART_HandleTypeDef huart1;

/* USER CODE BEGIN PV */
char msg[100] = {0};
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART1_UART_Init(void);
static void MX_TIM2_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

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

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_USART1_UART_Init();
  MX_TIM2_Init();
  /* USER CODE BEGIN 2 */

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  sprintf(msg, "test\r\n");
  while (1)
  {
      HAL_GPIO_TogglePin(LD1_GPIO_Port, LD1_Pin);
      HAL_GPIO_TogglePin(LD2_GPIO_Port, LD2_Pin);
      HAL_UART_Transmit(&huart1, msg, strlen(msg), 1000);
    /* USER CODE END WHILE */

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

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief TIM2 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM2_Init(void)
{

  /* USER CODE BEGIN TIM2_Init 0 */

  /* USER CODE END TIM2_Init 0 */

  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};

  /* USER CODE BEGIN TIM2_Init 1 */

  /* USER CODE END TIM2_Init 1 */
  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 25;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 9;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM2_Init 2 */

  /* USER CODE END TIM2_Init 2 */

}

/**
  * @brief USART1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_USART1_UART_Init(void)
{

  /* USER CODE BEGIN USART1_Init 0 */

  /* USER CODE END USART1_Init 0 */

  /* USER CODE BEGIN USART1_Init 1 */

  /* USER CODE END USART1_Init 1 */
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 19200;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_1;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX_RX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;
  huart1.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart1.Init.ClockPrescaler = UART_PRESCALER_DIV1;
  huart1.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_HalfDuplex_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetTxFifoThreshold(&huart1, UART_TXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetRxFifoThreshold(&huart1, UART_RXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_DisableFifoMode(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART1_Init 2 */

  /* USER CODE END USART1_Init 2 */

}

/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
/* 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_GPIOB_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOA, LD2_Pin|LD1_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(DUMMY_SIG_GPIO_Port, DUMMY_SIG_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pins : LD2_Pin LD1_Pin */
  GPIO_InitStruct.Pin = LD2_Pin|LD1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /*Configure GPIO pin : LINE_SIG_Pin */
  GPIO_InitStruct.Pin = LINE_SIG_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(LINE_SIG_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : DUMMY_SIG_Pin */
  GPIO_InitStruct.Pin = DUMMY_SIG_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(DUMMY_SIG_GPIO_Port, &GPIO_InitStruct);

/* 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 */

Please note that there's a couple of callbacks that have been disabled while testing.

stm32g4xx_hal_msp.c:

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file         stm32g4xx_hal_msp.c
  * @brief        This file provides code for the MSP Initialization
  *               and de-Initialization codes.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2024 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/* USER CODE END Header */

/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* USER CODE BEGIN Includes */

/* USER CODE END Includes */

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

/* USER CODE END TD */

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

/* USER CODE END Define */

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

/* USER CODE END Macro */

/* Private variables ---------------------------------------------------------*/
/* USER CODE BEGIN PV */

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* External functions --------------------------------------------------------*/
/* USER CODE BEGIN ExternalFunctions */

/* USER CODE END ExternalFunctions */

/* USER CODE BEGIN 0 */

/* USER CODE END 0 */
/**
  * Initializes the Global MSP.
  */
void HAL_MspInit(void)
{
  /* USER CODE BEGIN MspInit 0 */

  /* USER CODE END MspInit 0 */

  __HAL_RCC_SYSCFG_CLK_ENABLE();
  __HAL_RCC_PWR_CLK_ENABLE();

  /* System interrupt init*/

  /** Disable the internal Pull-Up in Dead Battery pins of UCPD peripheral
  */
  HAL_PWREx_DisableUCPDDeadBattery();

  /* USER CODE BEGIN MspInit 1 */

  /* USER CODE END MspInit 1 */
}

/**
* @brief TIM_Base MSP Initialization
* This function configures the hardware resources used in this example
* @param htim_base: TIM_Base handle pointer
* @retval None
*/
void HAL_TIM_Base_MspInit(TIM_HandleTypeDef* htim_base)
{
  if(htim_base->Instance==TIM2)
  {
  /* USER CODE BEGIN TIM2_MspInit 0 */

  /* USER CODE END TIM2_MspInit 0 */
    /* Peripheral clock enable */
    __HAL_RCC_TIM2_CLK_ENABLE();
    /* TIM2 interrupt Init */
    HAL_NVIC_SetPriority(TIM2_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(TIM2_IRQn);
  /* USER CODE BEGIN TIM2_MspInit 1 */

  /* USER CODE END TIM2_MspInit 1 */
  }

}

/**
* @brief TIM_Base MSP De-Initialization
* This function freeze the hardware resources used in this example
* @param htim_base: TIM_Base handle pointer
* @retval None
*/
void HAL_TIM_Base_MspDeInit(TIM_HandleTypeDef* htim_base)
{
  if(htim_base->Instance==TIM2)
  {
  /* USER CODE BEGIN TIM2_MspDeInit 0 */

  /* USER CODE END TIM2_MspDeInit 0 */
    /* Peripheral clock disable */
    __HAL_RCC_TIM2_CLK_DISABLE();

    /* TIM2 interrupt DeInit */
    HAL_NVIC_DisableIRQ(TIM2_IRQn);
  /* USER CODE BEGIN TIM2_MspDeInit 1 */

  /* USER CODE END TIM2_MspDeInit 1 */
  }

}

/**
* @brief UART MSP Initialization
* This function configures the hardware resources used in this example
* @param huart: UART handle pointer
* @retval None
*/
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
  if(huart->Instance==USART1)
  {
  /* USER CODE BEGIN USART1_MspInit 0 */

  /* USER CODE END USART1_MspInit 0 */

  /** Initializes the peripherals clocks
  */
    PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1;
    PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK2;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
    {
      Error_Handler();
    }

    /* Peripheral clock enable */
    __HAL_RCC_USART1_CLK_ENABLE();

    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**USART1 GPIO Configuration
    PA9     ------> USART1_TX
    */
    GPIO_InitStruct.Pin = USART1_TX_Pin;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF7_USART1;
    HAL_GPIO_Init(USART1_TX_GPIO_Port, &GPIO_InitStruct);

    /* USART1 interrupt Init */
    HAL_NVIC_SetPriority(USART1_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(USART1_IRQn);
  /* USER CODE BEGIN USART1_MspInit 1 */

  /* USER CODE END USART1_MspInit 1 */
  }

}

/**
* @brief UART MSP De-Initialization
* This function freeze the hardware resources used in this example
* @param huart: UART handle pointer
* @retval None
*/
void HAL_UART_MspDeInit(UART_HandleTypeDef* huart)
{
  if(huart->Instance==USART1)
  {
  /* USER CODE BEGIN USART1_MspDeInit 0 */

  /* USER CODE END USART1_MspDeInit 0 */
    /* Peripheral clock disable */
    __HAL_RCC_USART1_CLK_DISABLE();

    /**USART1 GPIO Configuration
    PA9     ------> USART1_TX
    */
    HAL_GPIO_DeInit(USART1_TX_GPIO_Port, USART1_TX_Pin);

    /* USART1 interrupt DeInit */
    HAL_NVIC_DisableIRQ(USART1_IRQn);
  /* USER CODE BEGIN USART1_MspDeInit 1 */

  /* USER CODE END USART1_MspDeInit 1 */
  }

}

/* USER CODE BEGIN 1 */

/* USER CODE END 1 */

Scope output

ST-Link connected: Scope output with ST-link connected

ST-Link disconnected: Scope output without ST-link connected

Schematic

I'm not sure if I can share the schematic since it's not mine - I'll ask if it's okay to share if it turns out to be necessary.

\$\endgroup\$
4
  • \$\begingroup\$ So where does the UART connect to? It works when connected to ST-LINK UART but no data when disconnected from ST-LINK UART? What is on the IO pin? How do you init the IO pin? You said it is a single wire half duplex mode. Show the schematics, source code, and how do you measure the pin. \$\endgroup\$
    – Justme
    Commented Mar 11 at 9:01
  • \$\begingroup\$ @Justme I've added more details - please let me know if this is enough. \$\endgroup\$
    – SirVer
    Commented Mar 11 at 10:16
  • \$\begingroup\$ No it isn't, the most important part, i.e. the initialization of the IO pin used for UART is missing. I think the function is called HAL_USART_MspInit(). But there's already enough hints what it could be, I just want to be sure. \$\endgroup\$
    – Justme
    Commented Mar 11 at 10:21
  • \$\begingroup\$ @Justme Sorry, forgot that that was in another file - I've added that now. \$\endgroup\$
    – SirVer
    Commented Mar 11 at 10:37

2 Answers 2

1
\$\begingroup\$

You have initialized the pin as open drain pin and without pull-up.

There is no reason to expect the pin ever to go high by itself, if there is no internal pull-up enabled or no external pull-up resistor connected.

Connecting it to ST-Link provides it a pull-up, either the ST-Link MCU enables an internal pull-up or has a physical resistor to pull the line up.

\$\endgroup\$
1
  • \$\begingroup\$ Welp, I feel silly now - I completely forgot that CubeIDE configures single wire UART as open drain by default. As you said, setting the pin to pull up does the trick. Thank you so much for the help! \$\endgroup\$
    – SirVer
    Commented Mar 11 at 11:45
0
\$\begingroup\$

You might be missing a common ground-connection in the UART to PC-connection. So that when the ST-link is connected the signal voltages are within spec, when it is disconnected they float out of range.

This is quite a common error with RS232-setups.

\$\endgroup\$
2
  • \$\begingroup\$ Hey, thanks for your response, but I'm not 100% sure what you mean, as I don't have a UART-to-PC connection apart from the ST-Link; I was using my scope to check the line, and there is a common ground between the scope and the board's power supply (which is also not connected to the PC). I'm also running the UART in single wire half-duplex mode, if that matters. \$\endgroup\$
    – SirVer
    Commented Mar 11 at 8:34
  • \$\begingroup\$ @SirVer That detail belongs to the question. Also other details about the schematics and connections. \$\endgroup\$
    – Justme
    Commented Mar 11 at 8:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.