Using Tools → Update Schematic from PCB is an important part of our reverse-engineering procedure, as we build the boards first, and then create the schematic from the board. Therefore, we name our global nets things meaningful to this process.
Replacing net with null, to stop the propagation of the default “unconnected-(U4-Pad1)” style names that show up by default. these names are very long, and get in the way of our schematic buildg process.
We’d like to get rid of them entirely, and then when a pin is marked as X (unconnected), then it doesn’t try to push a net name, so that just the “No Connection Flag” “X” symbol shows when we place it there, and no forced net name when we do Tools → Update Schematic from PCB.
That said, we want to force net names on everything that IS connected to a valid net, however, which is why this differentiation is important. When we make mistakes on the schematic by renameing wrong nets (which happens often enough in these complicated designs), we run Tools → Update Schematic from PCB
That said, I have considered just creating an “X” as a net name, but then the ratsnest will expect all of the disconnecteds to be connected to each other, which of coruse is wrong.
I have also done a bit of reverse engineering and have written:
In that tutorial I made extensive use of naming a net on the schematic, then use Schematic Editor / Tools / Update PCB from Schematic [F8] to put the changes onto the PCB, and then run DRC in the PCB editor to check for violations. This has the advantage that it is more in line with KiCad’s “normal workflow”, and you can put labels directly in the schematic to name your nets. I am not sure if the Schematic editor can even remember the name of a net if a net does not have a label, and thus you get the auto generated net names.
But for your original question…
Reverse-engineering is not the main goal of KiCad, and although tools for this are also slowly being implemented, progress is much slower then on other parts of KiCad.
A net can indeed be renamed from: PCB Editor / Tools / Net Inspector and the “Pencil” icon (while a line is selected)
For Reverse -engineering, it would be nice if the Schematic and PCB editors and their interactions were more symmetrical. But as I already mentioned, I think the Schematic can not remember a net name without an attached label. Another real boost for reverse-engineering would be if you could port the netlist from the PCB editor to the schematic editor, and then show ratsnest lines between schematic symbols. But this is not implemented, ans as far as I know, there is also no feature request for it.
Because the “forward” workflow is implemented far more completely then the reverse flow, I suggest you try labeling your nets in the schematic editor for a test, and then compare it with your current workflow.
Another possibility is to write a small helper script in the PCB editor (It has Python scripting support). You could write a loop that renames all “autogenerated” net names to some short net name. Names “aa” though “zz” already gives you 676 possible net names. You could include numbers too, but that can get confused with address and data lines such as “A0” and “D3”.
