ok i have two 1pps square waves, and i will xor them with each other, like as in 1 bit wire xor with a logic gate. which will give me a signal where rising edge to falling edge is the phase difference
i also have to guarantee that rising edge executes first and falling edge executes later and use 1 interrupt.
but with the xor solution (i drawed and checked it on paper) the output of the xor will tell me the time between them, but I would not know which one it is comes first
so (rtc xor sync) & !rtc gives signals if rtc falls to 0, and (rtc xor sync) & !sync gives signal if sync fall to 0 first.
so using 2 interrupts one for faster other for if pulse is lacking in phase
which will simplyfy coding