STM32 printf retarget to UART

uart.c

/*# 1- Identify the UART interface, GPIO pins and Alternate Function #########*/
/* For example:
 * B-L475E-IOT01A:
 * PB6     ------> USART1_TX
 * PB7     ------> USART1_RX
 * 
 * NUCLEO-L476RG:
 * PA2     ------> USART2_TX
 * PA3     ------> USART2_RX
 * 
 * STM32L4R9-DISCO:
 * PA2     ------> USART2_TX
 * PA3     ------> USART2_RX
 *
 * STM32H747I-DISCO:
 * PA9     ------> USART1_TX
 * PA10    ------> USART1_RX
 *
 */

/*# 2- Enable UART MODULE in Inc/stm32l4xx_hal_conf.h ########################*/
#define HAL_UART_MODULE_ENABLED

/*# 3- From Drivers/STM32L4xx_HAL_Driver/Src/ add the HAL UART C sources
    to your project: stm32xxxx_hal_uart.c stm32xxxx_hal_uart_ex.c ############*/

/*# 4- Create Global UART Handle in Src/main.c ###############################*/
UART_HandleTypeDef huart1;

/*# 5- Configure the UART interface in Src/main.c ############################*/

/**
 * @brief UART interface configuration
 */
void UART_Init(void)
{
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 115200;
  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.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
}

/*# 6- Configure the UART GPIOs  in Src/stm32l4xx_hal_msp.c ##################*/

/**
 * @brief UART MSP Initialization
 * @param huart: UART handle pointer
 */
void HAL_UART_MspInit(UART_HandleTypeDef* huart)
{
  GPIO_InitTypeDef GPIO_InitStruct;

  if (huart->Instance == USART1)
  {
    /* Peripheral clock enable */
    __HAL_RCC_USART1_CLK_ENABLE();

    /**
     * USART1 GPIO Configuration
     * PB6     ------> USART1_TX
     * PB7     ------> USART1_RX
     */
    /* Peripheral clock enable */
    __HAL_RCC_GPIOB_CLK_ENABLE();

    GPIO_InitStruct.Pin = GPIO_PIN_6 | GPIO_PIN_7;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF7_USART1;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
  }
}


/*# 7- Retarget printf to UART (std library and toolchain dependent) #########*/

#if defined(__GNUC__)
int _write(int fd, char * ptr, int len)
{
  HAL_UART_Transmit(&huart1, (uint8_t *) ptr, len, HAL_MAX_DELAY);
  return len;
}
#elif defined (__ICCARM__)
#include "LowLevelIOInterface.h"
size_t __write(int handle, const unsigned char * buffer, size_t size)
{
  HAL_UART_Transmit(&huart1, (uint8_t *) buffer, size, HAL_MAX_DELAY);
  return size;
}
#elif defined (__CC_ARM)
int fputc(int ch, FILE *f)
{
    HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
    return ch;
}
#endif

// OR:

// Add syscalls.c with GCC

#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */

/**
  * @brief  Retargets the C library printf function to the USART.
  * @param  None
  * @retval None
  */
PUTCHAR_PROTOTYPE
{
  HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
  return ch;
}