STM32+Keil 中使用printf函数

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 
* 
*

? COPYRIGHT 2012 STMicroelectronics

 
* 
* 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  
#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****/