Keil ARM-CM3 printf输出调试信息到Debug (printf) Viewer

参考资料：http://www.keil.com/support/man/docs/jlink/jlink_trace_itm_viewer.htm

1.Target Options -> Debug -> Settings(JLink) -> Debug里ort选择SW模式

2.在Target Options -> Debug -> Settings(JLink) -> Trace里选择Enable

3.Core freq设为120MHz（以LPC1788为例）

4. 设置ITM Port的值如下所示

5.在工程中添加.c文件如下

#include "stdio.h"

#define ITM_Port8(n)    (*((volatile unsigned char *)(0xE0000000+4*n)))
#define ITM_Port16(n)   (*((volatile unsigned short*)(0xE0000000+4*n)))
#define ITM_Port32(n)   (*((volatile unsigned long *)(0xE0000000+4*n)))

#define DEMCR           (*((volatile unsigned long *)(0xE000EDFC)))
#define TRCENA          0x01000000

struct __FILE { int handle; /* Add whatever you need here */ };
FILE __stdout;
FILE __stdin;

int fputc(int ch, FILE *f) {
  if (DEMCR & TRCENA) {
    while (ITM_Port32(0) == 0);
    ITM_Port8(0) = ch;
  }
  return(ch);
}

6.用Debug模式运行工程，Debug (printf) Viewer中即可以查看printf的输出信息。