描述

When I review the items analyzed for my constraints, I notice the number of paths increased compared to 8.x analysis. What caused this?

解决方案

A bug was found in the timing engine of the 8.x software that was fixed in the 9.x release. This bug caused some paths in the carry chain and input logic to be removed from analysis. This bug affected only Spartan-3 and Spartan-3e devices.

We recommend rerunning timing analysis with 9.x or 10.1 timing analyzer. If you are unable to migrate to 9.x or 10.1, you can add the following in your PCF:

For s3:

ENABLE = Tcinxb;

ENABLE = Tdiffin;

ENABLE = Tioftiq;

For s3e:

ENABLE = Tcinxb;