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[SignalTap] Storage Qualifier

Honored Contributor II

Hi All, 


I'm about the Storage Qualifier in SignalTap...  


What's the difference between the Transitional and Continuous qualifiers?  


I understand that Continuous qualifier captures data each clock while Transitional just when the signal value changes.  


So, with the Transitional qualifier, will I not see the "real" timing between the signals changes? Will I see just changes themselves?  


Let's say, there are two scenarioses: 

1) signal A raised and then after 50 clocks the signal B raised as well 

2) signal A raised and then after 100 clocks the signal B raised as well 


So, with the Continuous qualifier, will I be able to distinguish between two scenarios and with the Transitional will I not?  


Thank you!
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2 Replies
Honored Contributor II

That's the whole point of a storage qualifier. It doesn't show you the interim samples to save on-chip memory storage space. You can enable the option to display storage discontinuities (a line in the waveform view I believe), but it doesn't keep track of how many samples were thrown out in between. 


You should not rely on Signal Tap for timing, only functional verification.
Honored Contributor II

If I understand what you are asking, you want to know if you can get the time of a transition relative to other transitions. I've had similar problems and I don't think SignalTap has a built-in way to do this.  


I have not done this in a while, but as I remember, you can add your own counter clocked by the same clock as SignalTap. Add it to the SignalTap list, but make sure to exclude it from the signals that trigger a transition. Otherwise it itself will change every clock cycle making Transitional useless. The counter serves as an absolute time reference. 


This of course requires space to store the counter, which reduces the usefulness of Transitional, so make the counter as small as possible.