PWM Rise/Fall detection

Hi,

i'm programing a PWM read from a DI in an FPGA (NI 9425), this card doesn't accept fpga methods, so i need to figure out a way to detect when does it rise/fall, so with a sequence structure i can check the tick in wich this rise/fall ocurred and calculate the length of the high and low from the PWM...

Any ideas? I've been thinking all day, out of ideas right now...

Thanks!

Joan

PD: attached is the structure i have, next to the DI i need to place the rise/fall detector