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Altera_Forum's avatar
Altera_Forum
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9 years ago

Altera PLL timequest nets

Hello,

I have an Integer PLL instantiated in my Cyclone V SOC design.

In Timequest, I noticed 2 possible nets to choose from for this PLL:

1. "FRACTIONAL_PLL_O_VCOPH0"

2. "outclk_wire[0]"

Which one is correct for an Integer PLL ?

7 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    I assume you are talking about creating a generated clock for the output of the PLL. Instead of doing that, just use derive_pll_clocks. That automatically creates all the clock constraints for all PLL outputs, assuming you've constrained the input reference clocks.

  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    --- Quote Start ---

    I assume you are talking about creating a generated clock for the output of the PLL. Instead of doing that, just use derive_pll_clocks. That automatically creates all the clock constraints for all PLL outputs, assuming you've constrained the input reference clocks.

    --- Quote End ---

    No.

    I used "derive_pll_clocks" and:

    1. "FRACTIONAL_PLL_O_VCOPH0"

    2. "outclk_wire[0]"

    Are the names the tool gave to the PLL output clock.
  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    Is there any way to make Timequest name this clock after the HDL net name connected to it ?

  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    Where in Timequest are you looking? Sure you're not talking about SignalTap?

  • Altera_Forum's avatar
    Altera_Forum
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    9 years ago

    --- Quote Start ---

    Is there any way to make Timequest name this clock after the HDL net name connected to it ?

    --- Quote End ---

    Unfortunately, no. That's the caveat for using derive_pll_clocks. If you want to give the derived clocks custom names to make them easier to recognize in reports and use in other constraints, generate an SDC report (or write out an SDC file with the -expand option enabled) to see the standard create_generated_clock commands for your PLL outputs. Then add the -name option to those constraints with the names you want to use.