Input pulse interval measurement module to measure the frequency

I am using rh850d1m1a. To measure the frequency I am using input pulse interval measurement function. 

Read value of the CDR is keep on increamenting on every read, although input pulse is constant. It seems CNT register is not resetting to 0 after valid edge. 

May I know what could be the reason for this.

Valid edge is set falling edge. 

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