STM32+Keil 如何使用printf函数？

【lanmanck原创】

Keil不支持Host-semi机制，即不支持直接在IDE打印字符串。

那么只能通过程序向硬件串口发数据了，这样调用的时候用自定义的函数即可，也很方便，例如：

void send_char_to_usart(unsigned char c){}

但是可否直接使用printf函数呢？毕竟人家都做好了，我们给他定一个打印输出的接口就可以了，答案是肯定的，看ST的官方源码：

/**
  ******************************************************************************
  * @file    Lib_DEBUG/Lib_DEBUG_Example/main.c 
  * @author  MCD Application Team
  * @version V1.1.1
  * @date    13-April-2012
  * @brief   Main program body
  ******************************************************************************
  * @attention
  *
  * <h2><center>© COPYRIGHT 2012 STMicroelectronics</center></h2>
  *
  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        http://www.st.com/software_license_agreement_liberty_v2
  *
  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
  ******************************************************************************
  */

/* Includes ------------------------------------------------------------------*/
#include "stm32l1xx.h"
#include "stm32l1xx_ip_dbg.h"
#include <stdio.h>

#ifdef USE_STM32L152D_EVAL
#include "stm32l152d_eval.h"
#else
#include "stm32l152_eval.h"
#endif


/** @addtogroup STM32L1xx_StdPeriph_Examples
  * @{
  */

/** @addtogroup Lib_DEBUG_Example
  * @{
  */ 

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
USART_InitTypeDef USART_InitStructure;
 
/* Private function prototypes -----------------------------------------------*/
#ifdef __GNUC__
  /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf
     set to 'Yes') calls __io_putchar() */
  #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
  #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */

/* Private functions ---------------------------------------------------------*/

/**
  * @brief   Main program
  * @param  None
  * @retval None
  */
int main(void)
{
  /*!< At this stage the microcontroller clock setting is already configured, 
       this is done through SystemInit() function which is called from startup
       file (startup_stm32l1xx_xx.s) before to branch to application main.
       To reconfigure the default setting of SystemInit() function, refer to
       system_stm32l1xx.c file
     */     
       
  GPIO_InitTypeDef GPIOA_InitStructure;

  /* USARTx configured as follow:
        - BaudRate = 115200 baud  
        - Word Length = 8 Bits
        - One Stop Bit
        - No parity
        - Hardware flow control disabled (RTS and CTS signals)
        - Receive and transmit enabled
  */
  USART_InitStructure.USART_BaudRate = 115200;
  USART_InitStructure.USART_WordLength = USART_WordLength_8b;
  USART_InitStructure.USART_StopBits = USART_StopBits_1;
  USART_InitStructure.USART_Parity = USART_Parity_No;
  USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
  USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;

  STM_EVAL_COMInit(COM1, &USART_InitStructure);
 
  /* Initialize all peripherals pointers */
  IP_Debug();
  
  printf("\r\n STM32l1xx Firmware Library compiled with FULL ASSERT function... \n\r");
  printf("...Run-time checking enabled  \n\r");

  /* Simulate wrong parameter passed to library function ---------------------*/
  /* To enable SPI1 clock, RCC_APB2PeriphClockCmd function must be used and
     not RCC_APB1PeriphClockCmd */
  RCC_APB1PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);
  
  /* Some member of GPIOA_InitStructure structure are not initialized */
  GPIOA_InitStructure.GPIO_Pin = GPIO_Pin_6;
  GPIOA_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  /*GPIOA_InitStructure.GPIO_Speed = GPIO_Speed_40MHz;*/
  GPIOA_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIOA_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL; 
  GPIO_Init(GPIOA, &GPIOA_InitStructure);
  
  while (1)
  {
  }

}

#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 can add his own implementation to report the file name and line number */

  printf("\n\r Wrong parameter value detected on\r\n");
  printf("       file  %s\r\n", file);
  printf("       line  %d\r\n", line);
    
  /* Infinite loop */
  /* while (1)
  {
  } */
}
#endif

/**
  * @brief  Retargets the C library printf function to the USART.
  * @param  None
  * @retval None
  */
PUTCHAR_PROTOTYPE
{
  /* Place your implementation of fputc here */
  /* e.g. write a character to the USART */
  USART_SendData(EVAL_COM1, (uint8_t) ch);

  /* Loop until the end of transmission */
  while(USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC) == RESET)
  {
  }

  return ch;
}

/**
  * @}
  */ 

/**
  * @}
  */ 

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

该例子就是把COM1作为输出口，把printf的数据打印到该串口上，因此你需要一个串口线与STM32和电脑相连，这样就可以看到printf了。