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Propagated clocks

gchalive
How do i set propagated clocks in RC. Is there an equivalent command to the synopsys command set_propagated_clocks. Thanks

  •  Hi gchalive,

    RC does not have a propageted clocks nor does it perform hold analysis. In most cases, such operatins are best left for P&R. I am curious to find out what exactly do you need to do.

     gh-

  • Hi ,

    I have come across this in RC manual:
    "propagated_clocks_by_mode"
    Reading this attribute gives all the propagated clocks in the design..It that is the case then I am assuming there is a way to set a clock as proagated clock. Please confirm.

    I need to use this because my circuit has a generated clock and to get exact timing i need to set it as propagated clock. To be more clear, if I have a two stages of sequential elements, and the first stage outputs generates clock for the second stage flipflops.
    I would  need to make the complete block work in single clock. So while doing timing the clock arrival time of the second stage flipflop should be clock to q of first stage seq element+combinational delay that generates clock. This I can achieve only by propagating clocks.

    Thanks

  • Hi gchalive,

     the propaged_clocks attribute serves a different purpose and that is informing the user of the clock that was propagated to a certain sequential element. The ..._by_mode but also tell the user which clock got propagated in what timing mode in the the case of multi-mode designs. As indicated previously, the clocks in RC will always be ideal.

    Now, looking that design challenge you describe, the general practice is to rely on set_clock_latency or similar command to specify the latency on the generated clock and then run your clock tree tool targeting that latency (then again, the latency may not be CT related but simply a CK->Q or something like that ion which case it is a reasonably well defined value) Ultimately, addressing the propageted clock as a hard constraints when its final value will change due to unaccounted for physical and yield considerations, provides limited value hence the methodology.

    hope this helps clarify,

    gh-

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