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wangduoyu's avatar
wangduoyu
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1 month ago
Solved

[Agilex 5] Global Clock assignment ignored for PLL output clock with high fanout

Device: Agilex 5 Issue Description: The Timing Analysis report indicates that a specific PLL output clock has a fanout of 21343(see screenshot below). Does this high fanout on non-global routing...
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Core Logic
Generic Io
  • ShengN_altera's avatar
    ShengN_altera
    1 month ago

    I think they're same signal and had been pushed to global clock network. If you turn off global signal, the signal is not showed in Fitter's 'Global & Other Fast Signals' summary right?

    For clock, it's normal and healthy to still have high fanout even though had been pushed to global clock network (clock usually having high fanout). The global clock network will have low skew for those clock high fanout.

    The only problem is the high fanout clock but using regional routing, that'll causes skew issue.

sstrell's avatar
sstrell
Icon for Super Contributor rankSuper Contributor
1 month ago

No, you should be checking the Global signals report in the compilation report in the Fitter folder I believe since this is a resource placement issue.  A clock naturally has high fanout to drive everything but the global signals report indicates if the clock is using a global clock resource or being routing on standard routing wires.

  • wangduoyu's avatar
    wangduoyu
    Icon for New Contributor rankNew Contributor
    1 month ago

    The picture  is from the Fitter's 'Global & Other Fast Signals' summary. I believe this entry corresponds to the manual constraint I applied in the Assignment Editor.

    Could you please confirm if this is effectively the same signal as the one reported with a high fanout of 21,343 in the Timing Analyzer?

    Please advise. Thanks

    • ShengN_altera's avatar
      ShengN_altera
      Icon for Super Contributor rankSuper Contributor
      1 month ago

      I think they're same signal and had been pushed to global clock network. If you turn off global signal, the signal is not showed in Fitter's 'Global & Other Fast Signals' summary right?

      For clock, it's normal and healthy to still have high fanout even though had been pushed to global clock network (clock usually having high fanout). The global clock network will have low skew for those clock high fanout.

      The only problem is the high fanout clock but using regional routing, that'll causes skew issue.

      • wangduoyu's avatar
        wangduoyu
        Icon for New Contributor rankNew Contributor
        1 month ago

        I got it，thank you