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how max_sink_trans value is going to affect the timing of my design

gops

 Max_Sink_trans value specifies the clock slew, can some one please let me understand how it is going to affect the timing of my design? Please let me know if it has to be less than the max_transiton_delay in liberty file? or the max_transiton_delay is for the Dpins of the flip flops and max_sink_trans is not dependent on the transtion delay for which the library is characterized.thanks

  • The max_tran in the library is usually a looser number than what we set design targets for, but will accept at signoff. For example, if the .lib has a max tran of 1ns, we might want to set the design max tran for 700ps (in the SDC file). But as we near tapeout, we might allow transitions between 700ps and 1ns. As for the clock transitions, those are usually tighter still, so in this basic example, we might set the clock transition to 500ps. Again, if you have a few sinks that don't quite make that transition, as long as it's within the library limit, you should be ok. I hope I've understood your question correctly!

  •  HI Kari,

     

    thank you very much for the reply.Can you clarify the following queries pls.

    1) in the library there is a default_max_trans value .is this applicable for both "D" pin and "clk" pin of the flip flop in the library? or just for "D" pin.

     

    2) Can you pls elaborate on how the max_sink_trans value is going to affect delays of the flip flops?

  • i believe the default_max_transition will cover any pin that doesn't have a tighter constraint.

    for your second question, i'm not a timing expert, but you can look in the .lib tables and see how a transition in the range of what you specify to CTS would affect the delay vs. the max transistion. i'm not sure if i understand your question though. 

  • Hi madam,


    a small confusion in .ctstch file


    1.what are buffer_max_transition  sink_transition , how they effects on timing report

    2.is there any relation between  sink_transition and the cell_delay ?

    thanks in advance

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