What is a feedthrough path, and what happens if it isn't handled correctly?
From PDVerse Low-Power Physical Design Mentor Guide · pdVerse Mentor Guide
Explanation
A feedthrough path is a signal path that passes straight through a cell or macro from one side to the other without being logically transformed. It's flagged specifically in the context of pins that lack related power/ground pin information.
Implementation Walkthrough
The documented handling is narrow but specific: if a macro's pins don't have related power/ground pins AND are not part of a feedthrough path, the tool assumes those pins are simply unconnected. Feedthrough status is therefore one of the two conditions the tool checks before deciding a pin's PG connectivity is legitimately undefined rather than a real problem. The query command get_upf_port_attributes -feedthrough returns 'a collection of shorted pins,' which is how a feedthrough relationship is actually identified.
Command
get_upf_port_attributes -feedthroughSwitch-by-switch
-feedthrough: returns the collection of pins that are electrically
shorted together for the queried port/pin, i.e. the feedthrough
path.Expected Tool Behavior
When correctly identified, a feedthrough path lets the tool recognize that an otherwise unrelated-looking pin pair is actually one continuous electrical path through the cell, so it is not misclassified as unconnected or flagged as missing PG information.
Example
This topic is not covered in enough depth here to give a fully reliable answer beyond the get_upf_port_attributes -feedthrough / macro-pin-PG-inference statements.
Common Mistake
Failing to mark or identify a genuine feedthrough path, so the tool assumes the macro's pins are simply unconnected (because they lack related power/ground pins) rather than recognizing they carry a signal straight through.
Likely Error Or Warning
This topic is not covered in enough depth here to give a fully reliable answer for a specific error/warning message on mishandled feedthrough paths.
Debugging Approach
Run get_upf_port_attributes -feedthrough on the suspect pins to confirm whether the tool actually recognizes the shorted/feedthrough relationship.
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