cyclone v lvds serdes fractional corner pll clocking

thanks for the answer. rarely people these days have a will to give knowledge to others.

no pcb is not yet designed. yeah.. i also noticed that there are specific REFCLK pins on cyclone v and each pin has access to 2 corner plls simultaneously; one for top 2 corner plls and another for bottom 2 corner plls and buffer you mentioned is a good way around. otherwise the clocks will reach REFCLK pins with different propagation delays and will have a phase shift in relation to each other. OR, if i place a crystal oscillator exactly on the middle line of cyclone v; at right or left side ; and use exactly same length traces in this case they will reach REFCLK -s with similar propagation delays and should have no phase shift between each other... well... or i should place a clock buffer and distribute clock to REFCLK-s from there.

another way i guess is to drive clock to these 2 REFCLK - s right from the crystal oscillator, with different trace lengths; then analyze phase difference of the arrival of clocks to the REFCLK-s. and use pll phase shift ability to align pll output clocks to each other and with the incoming clock phase. only limitation here is the fact that phase shift control will not let you to have any value of phase shift. it has fixed increments as i remember. 1.5 degrees or something like this. i am talking too much i know :) but it is so easy to get lost in these things. when i'll get that i was trying to prove a foolishness it will be too late.

my boss tells me that he was spoiled by cyclone iv which allowed single REFCLK pin to reach all the plls on entire fpga. even while these plls were driving serdes lvds. but of course cyclone iv had it's drawbacks. some rx tx pins were not allowed to be placed next to each other and stuff like this. cyclone v overcame that limitation by fixing rx es and tx es in appropriate places. but gave us new limitations with REFCLK use.

one more small question, i tried to use tx pin as an rx. as i remember emulated lvds had an ability to use tx pin as a receiver. but here in cyclone v i can't find a way to switch pins to emulated lvds. they are kinda all fixed true lvds -es with OCT -s in it. cyclone iv had set of banks with emulated lvds pins. cyclone v has only true lvds es...