TMS320F28027: 程序开头printf正常输出，程序后面printf无输出

void main(void) 
{
// uint8_t print_cnt1=0,print_cnt2=0;
// Step 1. Initialize System Control:b
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the DSP2803x_SysCtrl.c  
   InitSysCtrl();
//  Clear all interrupts and initialize PIE vector table:
// Disable CPU interrupts
   DINT;
// Initialize PIE control registers to their default state.
// The default state is all PIE interrupts disabled and flags
// are cleared.
// This function is found in the DSP2803x_PieCtrl.c file.
   InitPieCtrl();
// Disable CPU interrupts and clear all CPU interrupt flags:
   IER = 0x0000;
   IFR = 0x0000;
// Initialize the PIE vector table with pointers to the shell Interrupt
// Service Routines (ISR).
// This will populate the entire table, even if the interrupt
// is not used in this example.  This is useful for debug purposes.
// The shell ISR routines are found in DSP2803x_DefaultIsr.c.
// This function is found in DSP2803x_PieVect.c.
   InitPieVectTable();

   // Copy time critical code and Flash setup code to RAM
   //实现在RAM中运行代码的搬运，例如使用官方的DELAY_US
   MemCopy(&RamfuncsLoadStart, &RamfuncsLoadEnd, &RamfuncsRunStart);
   InitMyGPIO();
   InitKEY();//按键

 SCI_Init();//波特率128000bps
 open_uart_debug();
   EALLOW;   
   PieVectTable.EPWM4_INT = &epwm4_isr;
   EDIS;
   InitEPWM_AQ_DB(); 
 printf("\r\n\r\n\r\nDSP is Ready");//标准C的printf输出测试，串口调试助手设置波特率128000bps，ASCII格式显示
i=1;
 printf("\r\n开发板左上角的J4排针（3针），用跳线帽短接靠左的2根针，即为将RG接入到模拟输入口B3");
 printf("\r\nPWM频率为19.6KHZ");
 //中断配置步骤-----5
 PieCtrlRegs.PIEIER3.bit.INTx4 = 1;    // Enable the PIE block
 PieCtrlRegs.PIECTRL.bit.ENPIE = 1;    // Enable the PIE block
 IER |= M_INT3;
 EINT;                                 // Enable Global interrupt INTM
 ERTM;//请参看 使用须知 文件夹下的   分享--ERTM、DRTM 在DSP编程中的作用.pdf
  printf("\r\nPWM频率为20KHZ 两路PWM");
    while(1) 
    {
    }
}