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@(cross) missing crossing?Why is

TerryL

Hello:

Can someone please tell me what I am doing wrong?

code snippet"

$strobe("LPIN report: @%rs => ov_check V(lpin, vssa):%r, ov_negate:%r", $abstime, V(lpin, vssa), ov_negate);

@(cross((V(lpin, vssa) - ov_negate), -1))
begin
  ov = 0;
  $strobe("LPIN report: @%rs => ov_off ov_negate:%r", $abstime, ov_negate);
end

output:

LPIN report: @51.8604ms => ov_check V(lpin, vssa):61.3485m, ov_negate:54.75m

LPIN report: @52.8437ms => ov_check V(lpin, vssa):52.8994m, ov_negate:54.75m

LPIN report: @54.6437ms => ov_check  V(lpin, vssa):37.4326m,  ov_negate:54.75m

Why is the @cross code not triggered as V(lpin, vssa) crosses 54.75mv ???

What am I missing?

  • TerryL
    I figured this out:

    It was simply a tolerance issue.
    cross (expr1 [ , direction [ , time_tol [ , expr_tol ] ] ] )
    The default expr_tol is:
    1e-9 + reltol*max_value_of_the_signal
    which in this case was:
    1e-9 + 1m*550 = 550mV

    I changed the cross call to:
    @(cross((V(lpin, vssa) - ov_negate), -1, 1, 10m))
    and the cross was detected.

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