calculation of time difference between two crossings of voltage waveforms in simulink

my project is sensorless control of four switch three phase brushless dc motor drive.to estimate the rotor position i have to compare the voltage waveforms of phase A and B.if we compare two waveforms we get four crossings in one revolution.these crossings show different rotor positions.how can i calculate the timings between two crossings?.i am using simulink.

Answer 1

[Manikandan]

Refer my paper: http://www.ripublication.com/ijaer_spl/ijaerv10n10_59.pdf