svc_handler pend_sv systick 三个中断
#define vPortSVCHandler SVC_Handler
#define xPortPendSVHandler PendSV_Handler
#define xPortSysTickHandler SysTick_Handler
点掉，不要生成。
注释掉
添加代码
int fputc(int ch, FILE *f)
{
HAL_UART_Transmit(&huart2, (uint8_t *)&ch, 1, 0xFFFF);
return ch;
}