CTPKS questions ?

Discussion in 'Cadence' started by mk, Nov 6, 2004.

  1. mk

    mk Guest

    Hi,
    I have two questions about CTPKS. I hope someone can answer them:

    1) Divided clock: I have a programmable clock divider and I can use
    the set_attribute ... ct_no_leaf "true Q" to put the generator flop
    into the tree and this is handled nicely (the generator flop gets a
    clock earlier in than other leaves so high speed clock to generated
    clock setup/hold is ok) but the flops which are used in the clock
    divider logic are connected as leaves and this causes a problem
    between the flop with the clock output and the divider logic flops.
    How do I tell CTPKS to move the divider logic flops (which are only
    driving the clock output flop) in the tree to the same location as the
    generator flop ?

    2) Manual useful skew: I have some IO flops which I want to move back
    in the clock tree manually. I have a buffer which drives the clock
    input of these flops and during synthesis, I put a clock_tree root
    constraint on it and a negative insertion delay to get what I want but
    how do I tell CTPKS to connect these IO flops to an point earlier in
    the clock tree than the other leaf registers ? Currently I am doing
    this manually after CTPKS.

    thanks for any and all help.
     
    mk, Nov 6, 2004
    #1
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