LEDblink example doubt

#include "DSP2833x_Device.h"     // DSP2833x Headerfile Include File   
#include "DSP2833x_Examples.h"   // DSP2833x Examples Include File   
   
// Prototype statements for functions found within this file.   
interrupt void cpu_timer0_isr(void);   
   
void main(void)   
{   
   
// Step 1. Initialize System Control:   
// PLL, WatchDog, enable Peripheral Clocks   
// This example function is found in the DSP2833x_SysCtrl.c file.   
   InitSysCtrl();   
   
// Step 2. Initalize GPIO:   
// This example function is found in the DSP2833x_Gpio.c file and   
// illustrates how to set the GPIO to it's default state.   
// InitGpio();  // Skipped for this example   
   
   
// Step 3. Clear all interrupts and initialize PIE vector table:   
// Disable CPU interrupts   
   DINT;   
   
// Initialize the 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 DSP2833x_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 DSP2833x_DefaultIsr.c.   
// This function is found in DSP2833x_PieVect.c.   
   InitPieVectTable();   
   
// Interrupts that are used in this example are re-mapped to   
// ISR functions found within this file.   
   EALLOW;  // This is needed to write to EALLOW protected registers   
   PieVectTable.TINT0 = &cpu_timer0_isr;   
   EDIS;    // This is needed to disable write to EALLOW protected registers   
   
// Step 4. Initialize the Device Peripheral. This function can be   
//         found in DSP2833x_CpuTimers.c   
   InitCpuTimers();   // For this example, only initialize the Cpu Timers   
#if (CPU_FRQ_150MHZ)   
// Configure CPU-Timer 0 to interrupt every 500 milliseconds:   
// 150MHz CPU Freq, 50 millisecond Period (in uSeconds)   
   ConfigCpuTimer(&CpuTimer0, 150, 500000);   
#endif   
#if (CPU_FRQ_100MHZ)   
// Configure CPU-Timer 0 to interrupt every 500 milliseconds:   
// 100MHz CPU Freq, 50 millisecond Period (in uSeconds)   
   ConfigCpuTimer(&CpuTimer0, 100, 500000);   
#endif   
   
// To ensure precise timing, use write-only instructions to write to the entire register. Therefore, if any   
// of the configuration bits are changed in ConfigCpuTimer and InitCpuTimers (in DSP2833x_CpuTimers.h), the   
// below settings must also be updated.   
   
   CpuTimer0Regs.TCR.all = 0x4001; // Use write-only instruction to set TSS bit = 0   
   
// Step 5. User specific code, enable interrupts:   
   
// Configure GPIO32 as a GPIO output pin   
   EALLOW;   
   GpioCtrlRegs.GPBMUX1.bit.GPIO32 = 0;   
   GpioCtrlRegs.GPBDIR.bit.GPIO32 = 1;   
   EDIS;   
   
// Enable CPU INT1 which is connected to CPU-Timer 0:   
   IER |= M_INT1;   
   
// Enable TINT0 in the PIE: Group 1 interrupt 7   
   PieCtrlRegs.PIEIER1.bit.INTx7 = 1;   
   
// Enable global Interrupts and higher priority real-time debug events:   
   EINT;   // Enable Global interrupt INTM   
   ERTM;   // Enable Global realtime interrupt DBGM   
   
// Step 6. IDLE loop. Just sit and loop forever (optional):   
   for(;;);   
}   
   
   
interrupt void cpu_timer0_isr(void)   
{   
   CpuTimer0.InterruptCount++;   
   GpioDataRegs.GPBTOGGLE.bit.GPIO32 = 1; // Toggle GPIO32 once per 500 milliseconds   
   // Acknowledge this interrupt to receive more interrupts from group 1   
   PieCtrlRegs.PIEACK.all = PIEACK_GROUP1;   
}