编译时候报错..
Library reports error: __use_no_semihosting was requested, but _ttywrch was referenced
上网找了解决方法
在usart.c文件的
_sys_exit(int x)
{
x = x;
}
大约47行后面加入
//__use_no_semihosting was requested, but _ttywrch was
_ttywrch(int ch)
{
ch = ch;
}
即可解决问题
原文：http://www.cnblogs.com/mingyunrangwozoudaoxianzai/p/6576475.html