08-12-2008 08:50 AM
Hi, me again ;) , I am working with MIG trying to attach a DDR2 to our Virtex5. There is code in the phy init unit that does not make sense to me, maybe I don't understand xst well enough to get it.
When assigning the ddr address and bank outputs during physical initialization there are multiple if clauses and finally there is the else clause that reads:
-- otherwise, cry me a river
ddr_ba_r <= (others => 'X');
ddr_addr_r <= (others => 'X');
(I like nice comments :) )
Besides having nasty 'X's in my simulation I don't understand how the synthesis tool shall/will handle this assignment. To me it would make more sense to assign '-' since this would tell the tool that it can insert either value that could help during optimization. Is this the behavior of xst or is there something else to it?
08-13-2008 01:06 PM