ContributorSignalTap does not show trigger pulse at the same sample number everytime
In SignalTap II it is possible to specify the trigger position as e.g as centre trigger position. When trigger condition is met, the sample number where the condition was met will always be at the same location e.g center of the display for center trigger position.
If we have selected 128 sample depth, the trigger condition will be around sample 64 *consistently*! The sample number where trigger condition is met will always appear on the same location every time SignalTap II triggers and shows the result.
In the past I have observed many times that when using segmented SignalTap II instance, we have a situation where for a given system, certain combinations of sample depth and segment count, the trigger point shows a jitter. This means that when data appears on SignalTap II after trigger condition being met, the trigger point sample number will be a few samples before or after the correct sample number. This only happens when segmented buffer is used! I have not been able to predict when this bug should happen so far. Using trial and error or by using a different combination of sample depth and segment count, it is possible to cause the problem to go away. The issue here is that since Quartus projects take such a long time to compile, it ends up wasting a huge amount of time trying to recompile project just to get SignalTap II to work consistently.
Why does signal tap have this bug? I am sure many other people have observed it as well at some point during their usage.
