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Honored Contributor I

SignalTap Can't Read Certain Signal



I'm having problem with SignalTap. I was trying to use SignalTap to compare the archived project with the current developing one (they're mostly the same). However, I couldn't read some of the signals from the old project. I know that it is functional and I shouldn't be reading 0 for those signals. I checked technology map (post-fitting) and found that the old project's SignalTap module has much fewer ports then the current one. I'm thinking maybe that's the problem cause I can only read the signal in SignalTap if it's in technology map. Can any of you guys give me some advice on how to add in the signals? 


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Honored Contributor I

It sounds like perhaps you've been tapping post-fit signals instead of pre-synthesis nodes. The weird names in the image you attached seem to confirm this. If changes are made to a design, there's no guarantee that post-fit signals will remain after another compilation, so Signaltap can't connect to them. I rarely tap post-fit nodes because of this. If you can, tap pre-synthesis nodes. These are also much easier to find because they are based directly off your HDL design. Use the Node Finder in Signaltap set to the pre-synthesis node filter or cross-probe to Signaltap from the RTL Viewer, not the Tech Map Viewer.