In the extreme DSP slice there are two registers before the multiplication on each of the A and B inputs. Does anyone know why you would need 2 registers before the multiplication?
At first I thought it may be a register similar to the one in a MULT18x18s, but changing the number of registers on A and B from 1 to 2 had no effect on timing. Also it wouldn't make sense since A and B are individually selectable to have 0,1, or 2 registers.
-Kevin