AR# 38239: XST 12.2/13.x - Global Equivalent Register Removal = NO does not work
XST 12.2/13.x - Global Equivalent Register Removal = NO does not work
A particular design contains replicated logic. In order to meet timing the Equivalent Register Removal XST property is set to NO. In spite of setting this property to NO, XST still produces the following informational message:
INFO:Xst:2261 - The FF/Latch XXX in Unit XXX is equivalent to the following XXX FFs/Latches, which will be removed :
How to do I ensure my replicated logic is not lost?
This is a known issue and was fixed in ISE 13.2 software. To work around this issue, place the equivalent register removal attribute on each individual net in you HDL. The attribute place on specific nets will be honored by XST.
Another possible workaround would be to add the following line in the .xcf file:
MODEL "entity_name " equivalent_register_removal=no;
Here entity_name is any entity that has some registers which XST considers to be equivalent.
Note that this method is less specific as it is applied to a whole entity.