I have an application that has 300 pins on a tri-stated bus. They have a tight offset constraint for the output time. Driving the T on the OBUFT for all those off the same line fails time spec because the fanout (of 300) stretches the time a little too long. In Synplicity, you turn on the duplicate register option, and it will duplicate the last register on the T line 300 times so that the timespec will pass. XST is clueless. It seems to not even care that it is failing timespec; it does no register duplication to fix failed OFFSET constraints. I had to duplicate the register myself by declaring a bunch of them. Anyone else seen the same issue?
- posted
18 years ago