Extract cell connections

[Licheng-Guo]

Hey Chris,

I'm trying to extract the primitive cells connected to a given module port.

I have a basic version working by first getting all desired EDIFHierCellInsts, then looking up their physical locations. However, what if a module is encrypted and we cannot see the EDIFNetlist? Can we extract connections through the physical netlist to bypass the encryption issue? Thanks!

[clavin-xlnx]

If the design is placed, all leaf cells will be present as Cell objects in the Design. If the design is also routed, Net objects with SitePinInst connections will be present also and can be used to trace to the Cell objects which have a 1:1 correspondence to their logical cell equivalents (EDIFHierCellInst/EDIFCellInst). Tracing a SitePinInst back to a Cell pin is a bit trickier, especially if the logical view is not available, but should be doable. There are some example helper methods in DesignTools that should be able to help or provide an example on how to traverse the SiteInst in order to see identify connections, here are a couple:

DesignTools.getConnnectedCells(SitePinInst)
DesignTools.getDrivingCell(SitePinInst)

[Licheng-Guo]

Thanks Chris, what if the design is only placed? Do you see a workaround to obtain connections between Cells?

[clavin-xlnx]

There isn't a clean solution for a placed DCP. You could route the design quickly in Vivado and bring it back into RapidWright or you could open the DCP in Vivado and (assuming the connections are visible) you could query the net connections with Tcl commands. But these are both slow.

If you knew ahead of time all of the IP that were to be encrypted, you could store a cache of implementations and then keep track of just the port connections you were interested in for making connections and then rely on those cached versions. This would require all IP to be marked with the DONT_TOUCH attribute in order to ensure that all versions would have the same port interface which is also undesirable.