i was just looking at virtex and stratix architectures. i observed that direction of carry chain is bottom to top and direction of shift chain is top to bottom for virtex devices, whereas it appears that both are in the same direction in stratix.
Just wondering if it is just a coincidence or is this intentional?
This doesn't address your question, but...
Be careful assuming that the shift register chains go top-to-bottom. They don't really. The dedicated routing resources for shift register chains only exist within the boundaries of a CLB. If the shift register chain expands across two CLBs for whatever reason, be it length of the chain or constraints, then the shift chain will have to use general routing resources at the CLB boundary.
-Davis
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