![Violation Violation](http://4.bp.blogspot.com/-0ZaBq_XnDAY/TZ28vKSws1I/AAAAAAAAADY/crVbiEOE39Q/s1600/Setup+and+Hold+3.bmp)
What is Hold time?The hold time is the intervalafter the clock where the data must be held stable. Hold time can benegative, which means the data can change slightly before the clock edgeand still be properly captured. Most of the current day flip-flops haszero or negative hold time.Way of fixing the hold time violation is just opposite of setup time violation.Below are few methods to fix hold time violation.1. Introducing the delay in data path, you can do this by adding the buffers in data path2.
Downsizing the cells3. VT swapping, you can swap the the LVT buffers to SVT or HVT buffers.
If the Hold Time Violation is associated with a PERIOD constraint, the data path is faster than the clock skew. The resolution is similar to a Hold Time Violation in an OFFSET IN constraint, but decrease the clock skew instead of just the clock path delay. To decrease the clock path skew, verify that the design is using the global clocking resources.