Why primetime returns infinity slack for some nodes?

[ebrahimi.khoy]

I wrote a very simple code to extract the slack time of all flip-flops:

foreach_in_collection pin [get_pins */D] {
set pinName [get_attribute $pin full_name]
set riseSlack [get_attribute $pin max_rise_slack]
set fallSlack [get_attribute $pin max_fall_slack]
puts "$pinName $riseSlack $fallSlack"
}


I don't know why I got INFINITY as output for some flip-flops?
What does infinity slack time means?

 

[OhaAmo]

Maybe those pins are inputs of your design, and unconstrained.
If an input pin is unconstrained, then the tool cannot estimate what is the input slack on it and might return you with infinity.
You should constrain every input/output pin to avoid those kind of mistakes.