MSP430F5438 Capture Mode

Hello 

I am trying to use the capture mode

Main Clk Source: SMCLK

Internal Signal: ACLK 

The problem is it keeps getting stuck in the while loop. Can you please help me out

TBCTL = TBSSEL_2 + MC_2 + TBCLR; //MC_2 | TBSSEL_2, SMCLK, CONT Mode
TB0CCTL6 = CM_1 | CAP | CCIS_1;
//TB0CCR6 = 0x32;
while(1)
{
while(!(TB0CCTL6 & CCIFG));                     //gets stuck here

TB0CCTL6 &= ~CCIFG;

}