[verilog] trigger selection of rising and falling edge

[gunkaragoz]

hi. now i'm trying to realize a digital backend for a 200 msps data acquisition system with verilog. actually this is the digital part of a digital storage oscilloscope.

i have a problem with trigger module. i want trigger mode(posedge or negedge) to be selected. but as i know i cannot use if statement before always block. how can i do the selection?