Microcontroller stucks when uart not connected

[SA.17]

i am using stm32L072

I am using uart1 in the code

I found that code doesn't works ,if i don't connect a usb to uart converter between PC and the microcontroller .

When i connect usb to uart connector and reset microcontroller ,it starts working :weary_face: or if i comment uart_init function ,the code works fine without usb-uart converter .

What might be the issue ?

Below is uart initialization code :

static void MX_USART1_UART_Init(void)
{
 
  /* USER CODE BEGIN USART1_Init 0 */
/* (1) Enable GPIO clock and configures the USART pins *********************/
 
  /* Enable the peripheral clock of GPIO Port */
  USARTx_GPIO_CLK_ENABLE();
 
  /* Configure Tx Pin as : Alternate function, High Speed, Push pull, Pull up */
  LL_GPIO_SetPinMode(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_MODE_ALTERNATE);
  USARTx_SET_TX_GPIO_AF();
  LL_GPIO_SetPinSpeed(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_SPEED_FREQ_LOW);
  LL_GPIO_SetPinOutputType(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
  LL_GPIO_SetPinPull(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_PULL_UP);
 
  /* Configure Rx Pin as : Alternate function, High Speed, Push pull, Pull up */
  LL_GPIO_SetPinMode(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_MODE_ALTERNATE);
  USARTx_SET_RX_GPIO_AF();
  LL_GPIO_SetPinSpeed(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_SPEED_FREQ_LOW);
  LL_GPIO_SetPinOutputType(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
  LL_GPIO_SetPinPull(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_PULL_UP);
 
  /* (2) NVIC Configuration for USART interrupts */
  /*  - Set priority for USARTx_IRQn */
  /*  - Enable USARTx_IRQn */
  NVIC_SetPriority(USARTx_IRQn, 0);  
  NVIC_EnableIRQ(USARTx_IRQn);
 
  /* (3) Enable USART peripheral clock and clock source ***********************/
  USARTx_CLK_ENABLE();
 
  /* Set clock source */
  USARTx_CLK_SOURCE();
 
  /* (4) Configure USART functional parameters ********************************/
  
  /* Disable USART prior modifying configuration registers */
  /* Note: Commented as corresponding to Reset value */
  // LL_USART_Disable(USARTx_INSTANCE);
 
  /* TX/RX direction */
  LL_USART_SetTransferDirection(USARTx_INSTANCE, LL_USART_DIRECTION_TX_RX);
 
  /* 8 data bit, 1 start bit, 1 stop bit, no parity */
  LL_USART_ConfigCharacter(USARTx_INSTANCE, LL_USART_DATAWIDTH_8B, LL_USART_PARITY_NONE, LL_USART_STOPBITS_1);
 
  /* No Hardware Flow control */
  /* Reset value is LL_USART_HWCONTROL_NONE */
  // LL_USART_SetHWFlowCtrl(USARTx_INSTANCE, LL_USART_HWCONTROL_NONE);
 
 
 
  /* Set Baudrate to 115200 using APB frequency set to 16000000 Hz */
  /* Frequency available for USART peripheral can also be calculated through LL RCC macro */
  /* Ex :
      Periphclk = LL_RCC_GetUSARTClockFreq(Instance); or LL_RCC_GetUARTClockFreq(Instance); depending on USART/UART instance
  
      In this example, Peripheral Clock is expected to be equal to 16000000 Hz => equal to SystemCoreClock
  */
  LL_USART_SetBaudRate(USARTx_INSTANCE, SystemCoreClock, LL_USART_OVERSAMPLING_16, 115200); 
 
  /* (5) Enable USART *********************************************************/
  LL_USART_Enable(USARTx_INSTANCE);
 
  /* Polling USART initialisation */
  while((!(LL_USART_IsActiveFlag_TEACK(USARTx_INSTANCE))) || (!(LL_USART_IsActiveFlag_REACK(USARTx_INSTANCE))))
  { 
  }
 
  /* Enable RXNE and Error interrupts */
  LL_USART_EnableIT_RXNE(USARTx_INSTANCE);
  LL_USART_EnableIT_ERROR(USARTx_INSTANCE);
  /* USER CODE END USART1_Init 0 */