msp430g2553 pwm signal

Other Parts Discussed in Thread: MSP430G2553

Hi Everyone , 
I look that are there any exist topic about my question but i could not find 

I am working on generating pwm signal by using msp430g2553 . During wathcing the signal on oscilloscope , I released that , After the every 2 ms , The pin becomes high during 2.1ms . According to me , It should not happen .  What is the problem ?

Thank you

#include <msp430.h>
#include <stdint.h>

void pwm_init(void){
	 TA1CTL = TASSEL_2; // TimerA1 SMLCK
	 TA1CCTL1 = OUTMOD_7 | CCIE;  // The output is reset when the timer counts to the TACCRx value. It is set when the timer counts to the TACCR0 value.
	 TA1CCR1 = 0;

}

void pwm_start(void){
	TA1CTL |= MC_1;
}

void pwm_stop(void){
	TA1CTL = MC_0; // pwm is stopped by setting to zero pwm bandwidth
}

void pwm_set_duty(uint16_t frequency,int16_t rate){ // rate = percentage of duty cycle
	TA1CCR0 = frequency;
	pwm_start();
	if(rate >= 100) // Rate must be in range of 0,100 .this algrotihm keeps the rate in valid interval
		TA1CCR1 = 100;
	else if(rate <= 0 ){
		pwm_stop();
		TA1CCR1 = 0;
	}
	else
		rate%=100;
	rate*=frequency;
	TA1CCR1 = rate - 1;
}


void main(void){
    WDTCTL = WDTPW | WDTHOLD;	// Stop watchdog timer
    BCSCTL1 = CALBC1_1MHZ;
    DCOCTL = CALDCO_1MHZ;
    P2DIR |= BIT1;
    P2SEL |= BIT1;
    pwm_init();
    pwm_start();
    while(1){
    	pwm_set_duty(1000,100);
    }
}