STM32+Keil 如何使用printf函数？

【lanmanck原创:http://blog.csdn.net/lanmanck/article/details/17411921】

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。