Max delay and Min delay on same data path

Question

Hello, 
I am trying to set up timing constraints (both max and min delay) on a data path between two combinatorial elements. 
I use set_max_delay -from [get_pins pin name] -to [get_pins pin name] 6 -datapath_only 
        set_min_delay -from [get_pins pin name] -to [get_pins pin name] 4 
I checked the timing report and I see that the max_delay constraint is satisfied but the min_delay is not.What can be the reason behind this? 
Also, when i comment out the first line (max_delay constraint), I see that min_delay constraint is satisfied. 
Can't a datapath have both max and min delay constraints?
Any help will be really appreciated. 
Thanks! 
-Kamath 

Answer 1

Be very careful about trying to set max/min delays on a portion of a path (i.e. not from a valid startpoint to a valid endpoint). Doing so is called path segmentation. When you do so, the max/min delay gets applied to the portion of the path you specified, but the rest of the path (between the startpoint and the set_max_delay -from and from the set_max_delay -to to the endpoint) are no longer constrained at all.
There are extremely few reasons to want to do this. I second the question "Why do you want to do this?"
That being said, you can set both a max and min delay on the same path (or path segment, if you insist on segmenting the path). The set_max_delay overrides the setup requirement, and the set_min_delay overrides the hold requirement. If the two values are too close together the tools will not be able to satisfy both; all timing checks are done at both process corners (max PVT and min PVT) - the ratio from max to min is generally around 3:1, so if the set_max_delay is less than 3x the set_min_delay the tools will be unable to satisfy both (due to real, physical limitations).
Avrum