msp430 fr5994 改变全局变量或静态变量就会出现问题？

#include <msp430.h>
#include "driverlib.h"
#include <clk16.h>

/**
* main.c
*/
uint8_t i=0;
void main(void)
{
clk16();
Timer_A_clearTimerInterrupt(TIMER_A0_BASE);
Timer_A_initUpModeParam param;
param.clockSource=TIMER_A_CLOCKSOURCE_SMCLK;
param.clockSourceDivider=TIMER_A_CLOCKSOURCE_DIVIDER_32;
param.timerPeriod=50000;
param.captureCompareInterruptEnable_CCR0_CCIE=TIMER_A_CCIE_CCR0_INTERRUPT_ENABLE;
param.timerClear=TIMER_A_DO_CLEAR;
param.startTimer=false;

i=3;

Timer_A_initUpMode(TIMER_A0_BASE,&param);
GPIO_setAsOutputPin(GPIO_PORT_P1,GPIO_PIN0);
Timer_A_startCounter(TIMER_A0_BASE,
TIMER_A_CONTINUOUS_MODE
);
__bis_SR_register(LPM0_bits + GIE);

}

#pragma vector = TIMER0_A0_VECTOR
__interrupt
void Timer_A0_ISR(void)
{

if(Timer_A_getInterruptStatus(TIMER_A0_BASE))
{

GPIO_setOutputHighOnPin(GPIO_PORT_P1,GPIO_PIN2);

Timer_A_clearTimerInterrupt(TIMER_A0_BASE);
}

}

如上代码，i=3存在，则debug 打断点无法进入定时器中断，删掉i=3，则可以进入中断