pepijndevos changed the topic of #apicula to: Project Apicula: bitstream documentation and tooling for Gowin FPGAs https://github.com/YosysHQ/apicula -- logs https://freenode.irclog.whitequark.org/apicula
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<pepijndevos> omnitechnomancer, huh? can you elaborate?
<omnitechnomancer> this wasnt global clock trees it was regular intertile routing, which I could fuzz by submitting arbitrary route pips in a low level format, but near the edge of the grid the intertile wires loop back or connect differently, so doing the fuzzing on an edge tile makes a routing database that doesnt work because nextpnr tries to use those connections on tiles where they arent present
<pepijndevos> Ah yea, same. Gowin routing also wraps around.
<omnitechnomancer> I never wound up investigating how it wrapped but just ignoring them was okay for what I did
<pepijndevos> hehe
<pepijndevos> it's basically just as if they put a mirror at the edge
<omnitechnomancer> I expect its the same but never verified it
<omnitechnomancer> I just watched your talk on synthesis to 7400 series logic, I am wondering how large a design could be made and still reasonably meet timing at some reasonable clock speed
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* Lofty cries in having done the difficult part of Yosys for 7400 and getting ignored by omnitechnomancer
<Lofty> The repo is even on my account!
<Lofty> Anyway, it depends on your logic family of choice
<Lofty> A good rule of thumb for 74LVC is that each level of logic adds 4ns of delay
<Lofty> 74HC is more like 10ns
<pepijndevos> I think we figured 20MHz would be within range for a small CPU? That was potentially optimistic.
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<omnitechnomancer> I haven't looked at the actual implementation so I didn't know you did the yosys bit lofty :(
<Lofty> I swear Pepijn mentioned it in the presentation ^^;
<omnitechnomancer> Is the delay from PCB traces significant?
<Lofty> I don't know as of yet
<daveshah> I suspect that input capacitance will be more significant than PCB trace capacitance
<Lofty> Presently I can't model either~
<omnitechnomancer> At what kind of frequencies does length difference on the order of under a metre start to matter?