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Registered: ‎11-06-2011

Problem with Spartan 6 PCI "BYPASS" constraint

I am evaluating a PCI core from another vendor.

The .ucf file which came with the core attached the BYPASS constraint to all of the core's external I/O pins.

Implementing the core, I could not get it to work.

Using Chipscope, I found that no external pin stimulus was getting through the IBUFs on any of the I/O pins.

I verified that signals were changing on external pins using an o-scope, but Chipscope showed nothing changing inside.

All output buffers were tri-stated, as verified by Chipscope on the buffer's control pins.

The map report did not indicate that any of this logic was removed.


Anyway, I commented out the BYPASS constraints in the ucf, and everything worked fine after that.


The only info I could find on BYPASS was AR# 22137, which was confusing to me.

If BYPASS does not apply to Spartan 6, the mapper should ignore it.

What gives?

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