Problem: Compute distance with msp430, interrupt issue

Hello everyone. I'm trying to compute distance using msp430G2553 and SRF05. The connections pin are shown below:

SRF05 ======> MSP430

trigger =======> P1.7

echo    =======> P2.1

I didn't know why the interruption on P2.1 happened a lot of times (one time for if(P2IN & BIT1  == BIT1) and many times for else after). And the distance value was wrong.

Here is my code (I use CCS 6.2.0). Sorry, I don't know how to embed .rar file. The uart_puts() and uart_put_num() just write a string and a number to terminal, respectively.

/* Description: compute distance and show on the terminal via UART
 * CONNECT: VCC --> 5V
 * 			TRIGGER --> P1.7
 * 			ECHO --> P2.1
 * 			GND --> GND
 * 			NC --> no connect
 */
// khong nhay vao ngat

#include <msp430g2553.h>
//#include <intrinsics.h>
#include "uart.h"
#define	trigger		BIT7;
#define	 echo		BIT1;

void timer_init(void);
void trig(void);

unsigned int t1=0, t2=0, distance=100;


void main(void){
	WDTCTL = WDTPW | WDTHOLD;
	BCSCTL1 = CALBC1_1MHZ;
	DCOCTL =  CALDCO_1MHZ;

	P1DIR |= trigger;		// trigger ouput
	P1OUT &= ~trigger;
	P2DIR &= ~echo
	P2SEL |= echo;			//
	uart_init();
	timer_init();
	_BIS_SR(GIE);			// global interrupt enable
//	uart_puts("------\r\n");
	while (1){
		trig();
//		uart_puts("-----1\r\n");
		__delay_cycles(30000);		//  30ms time out
//		uart_puts("----2\r\n");

	}

}


void timer_init(void){
	TA1CTL = TASSEL_2 + MC_2;		// SMCLK; continuos mode, 0 --> FFFF
	TA1CCTL1 = CM_3 + CAP + CCIS_0 + SCS+ CCIE;		// falling edge & raising edge, capture mode, capture/compare interrupt enable
	// P2.1 (echo) is connected to CCIA (capture/compare input )
	TA1CCTL1 &= ~ CCIFG;
}

void trig(void){
	P1OUT |= trigger;
	__delay_cycles(20);
	P1OUT &= ~trigger;
}



#pragma vector = TIMER1_A1_VECTOR
__interrupt void compute_distance(void){
	uart_puts("--6\r\n"); // Just test
	switch(_even_in_range(TA1IV,0x0e)){
	    case TA1IV_NONE:

	    	break; // no more interrupts pending, exit ISR here.
	    case TA1IV_TACCR1: {		// CCR1 interrupt
	    	if (P2IN & BIT1 == BIT1) {		//  detect rising edge
	    			t1 = TA1CCR1;

	    		}
	    		else {						// and falling edge
	    			t2 = TA1CCR1;

	    			if (t2 > t1){
	    				distance = (t2-t1)/58;
	    				uart_put_num(distance,0,0);
	    				uart_puts("\r\n");
	    			}

	    		}
	    	break;
	    }
	    case TA1IV_TACCR2:
	    	break; // CCR2 interrupt
	    case TA1IV_6:
	    	break;
	    case TA1IV_8:
	    	break;
	    case TA1IV_TAIFG:
	    	break; // timer overflow
	    default:
	    	break;
	  }

	TA1CCTL1 &= ~ CCIFG;
}