I have been designing using the Virtex-II family in the FG456/FG676 footprints.
I imagine that there is a nice left-to-right data flow on-chip which fits nicely onto the CLBs, which increase in address from the left to the right as seen from above. Just like one would expect a schematic of a board of MSI logic to have.
I want to make a board with a similar layout (data sources to the left, sinks to the right) but I need to use a bigger chip.
I have just noticed that the FF896/FF1152 footprints have the die flipped over.
This seems to mean that data on my board will have to flow "right-to-left" inside the FPGA. From larger X addresses to smaller ones.
What's the story here?
Two questions:
1) Why didn't Xilinx mirror the masks on their larger chips (4000, 6000, 8000) so that flip-chip bonding of the big chip would result in identical CLB placement, as seen from above, as you get with the non-flipped smaller chips?
2) If I take a design which flows left-to-right in a non-flipped package and re-PAR it into a flipped package, will the performance be impacted? Percentage?
(For instance, I replace an XC2V2000 in FG676 with an XC2V2000 in FF896, with the same PC board layout of data-in/data-out but a slightly bigger chip area)
Thanks for the benefit of your experience:
Lawrence NoSpam