Physical Design
Getting negative slack after CTS in ICC2. Already tried adjusting clock uncertainty. What else should I check?
My setup was clean before CTS but now I have negative slack on a handful of paths. I lowered clock uncertainty but it barely moved. Where do I look next before I start throwing optimization at it?
arjun_pd3 hours ago
1 reply
Answer from SiliconPath
After CTS, check your insertion delay first. If the clock tree came out deeper than expected, the clock reaches your flops later, and that shows up as the setup slack going negative. Open the CTS report and look at the maximum insertion delay before you change anything. Next, make sure CTS only used proper clock buffers. If it picked up normal buffers, the tree will not balance well and the slack will stay. Fix those two things first, then run optimization.
SiliconPath · 2 hours ago