si_bundle_skew module

Skew across a bundle of differential pairs, with one leg as the guide.

ConstrainReferenceDifference(guide, topologies) checks the delay of each topology against the guide’s. The guide must run between single pins: passing a pair raises ValueError: Guide must be a single pin type. So for skew across pairs, one leg of one pair is the guide, here Topology(tx.lane0.p, rx.lane0.p), and both legs of the other pair are the targets. The same call matches data lines to a clock or strobe, with the clock’s single-ended path as the guide.

timing_difference(window) is checked as guide delay minus target delay against the window as written. The printed Target drops the sign: a window of -1000 ps to 0 and one of 0 to 1000 ps both print 500ps ± 500ps. Read the verdict from group.satisfied, never the direction from the text.

The pairs also carry a ConstrainDiffPair for intra-pair skew and the differential structure. The limits are illustrative.

Checked with the design-issues query, run as a script from a project root with that project’s runtime running (jitx 4.6.0rc10, runtime 4.6.0-rc.16):

import jitx

from jitxexamples.patterns.si_bundle_skew import BundleSkewDesign


def main() -> None:
    with jitx.runtime as rt:
        report = rt.submit(BundleSkewDesign).issues(satisfied=True, wait=30)
        if not report.complete:
            print("report incomplete: raise wait and run again")
        for group in report.groups():
            print("met" if group.satisfied else "NOT MET", group.text)
            if len(group.issues) > 1:
                for issue in group:
                    print("   ", issue.text)


if __name__ == "__main__":
    main()

It printed:

met Skew: 0s - Target: ± 2ps (longer from tx.lane0.p to rx.lane0.p, shorter from tx.lane0.n to rx.lane0.n)
met Skew: 0s - Target: ± 2ps (longer from tx.lane1.p to rx.lane1.p, shorter from tx.lane1.n to rx.lane1.n)
met Skew: 0s - Target: ± 10ps (longer from tx.lane0.p to rx.lane0.p, shorter from tx.lane1.p to rx.lane1.p)
met Skew: 0s - Target: ± 10ps (longer from tx.lane0.p to rx.lane0.p, shorter from tx.lane1.n to rx.lane1.n)
met Satisfied

Each pair’s intra-pair skew gives one line, and the bundle constraint one line per compared leg: two here, lane0.p against lane1.p and against lane1.n.

The last line is the Routing category’s group: every code route was made. It is not a constraint verdict.

class BundleSkew

Bases: Circuit

Two differential lanes matched to each other, with one leg of lane0 as the guide.

class BundleSkewDesign(*args, **kwargs)

Bases: SampleDesign

The matched lanes on the sample board.

circuit: Circuit = BundleSkew()