Ripple clock warning

Discussion in 'VHDL' started by ALuPin, Oct 5, 2004.

  1. ALuPin

    ALuPin Guest

    Hi,

    I have a question concerning my multi-clock design.

    A PLL is fed with a 30MHz external clock.

    There are three different clocks generated by the PLL:

    c0 : 48MHz (for internal use)
    c1 : 90MHz (for internal use)
    e0 : 90MHz (for external use)

    Apart from that I have a clock divider which generates an
    12MHz clock out of c0 and an inverted 90MHz clock out of c1.


    When I compile the whole design I get the following warnings:

    1.Found 1 node(s) in clock paths which may be acting as ripple and/or
    gated clocks -- node(s) analyzed as buffer(s) resulting in clock skew
    Info: Detected ripple clock CLOCK_DIVIDER

    Do I have to make some assignment for that? How?

    I would appreciate your help.

    Rgds
    André
    ALuPin, Oct 5, 2004
    #1
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  2. ALuPin

    Jeroen Guest

    "ALuPin" <> wrote in message
    news:...
    > Hi,
    >
    > I have a question concerning my multi-clock design.
    >
    > A PLL is fed with a 30MHz external clock.
    >
    > There are three different clocks generated by the PLL:
    >
    > c0 : 48MHz (for internal use)
    > c1 : 90MHz (for internal use)
    > e0 : 90MHz (for external use)
    >
    > Apart from that I have a clock divider which generates an
    > 12MHz clock out of c0 and an inverted 90MHz clock out of c1.
    >
    >
    > When I compile the whole design I get the following warnings:
    >
    > 1.Found 1 node(s) in clock paths which may be acting as ripple and/or
    > gated clocks -- node(s) analyzed as buffer(s) resulting in clock skew
    > Info: Detected ripple clock CLOCK_DIVIDER
    >
    > Do I have to make some assignment for that? How?
    >
    > I would appreciate your help.
    >
    > Rgds
    > André


    How did you implement that divider?? It seems from this message that you use
    a ripple counter, instead of a synchronous one.

    jeroen
    Jeroen, Oct 5, 2004
    #2
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  3. ALuPin

    ALuPin Guest

    >
    > How did you implement that divider?? It seems from this message that you use
    > a ripple counter, instead of a synchronous one.
    >
    > jeroen



    No it is a full synchronous one.


    I use QuartusII version 4.1 SP2


    Rgds
    André
    ALuPin, Oct 6, 2004
    #3
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