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Altera_Forum's avatar
Altera_Forum
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12 years ago

Dedicated clock routed globally to PLL

Hello all,

I'm currently developing a project with a display driving IP-core supplied by a manufacturer. The IP-Core utilizes two PLL's for DDR2 memory, while I also use one PLL for LVDS deserializing. The two PLLs used for DDR2 memory use both the same clock that is fed in by a dedicated clock pin, this however leads to a problem.

The (dedicated) clock that should feed both PLLs is routed global to both PLLs. Consequence is that the routed paths to the PLLs are not compensated, because of this i can't achieve timing closure.

The clock that should feed into these PLLs is connected to a dedicated clock pin (CLK7..4), and is feeding PLL2 and PLL4. According to the Cyclone 3 handbook Chapter-5 Figure5-2 The clock should be able to feed both the PLLs WITHOUT Being routed as a global clock. The clock is not used for anything else except feeding the two PLLs. Quartus also gives me a critical warning, that the PLLs are not driven by a dedicated clock and that this can cause issues.

I'm developing for the Cyclone 3 family (ep3c16 and up) and I am using Quartus 10.1 SP1 full version (for compatibility with IP-Core). How can i keep this clock from routing globally to the PLLs?

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor

    Fixed it by deleting the db and temp folders in the project. Fixed several other errors too.

    Shame on you Altera for not having a clean function.