Cross Coverage · SystemVerilog

Part 5 · Functional Coverage · Intermediate

5topics
5lessons

Coverpoints prove each field took its interesting values in isolation. Cross coverage proves the combinations occurred, which is where interaction bugs hide.

Two coverpoints, cp_op with 4 bins and cp_len with 3, feed a 12-cell cross. Three lessons work on that cross: selecting cells with binsof and intersect, pruning cells with ignore_bins and illegal_bins, and controlling explosion. All three lead to the last lesson, intent-driven patterns that turn spec rows into named cross bins.

The Cross Coverage topic in one picture.

Lesson	You will build…
Cross Basics	The 12-cell product matrix, auto bin naming, and three-point crosses.
binsof & intersect	Named selections over the matrix with AND, OR, NOT and value filters.
Pruning Crosses: ignore_bins & illegal_bins	Goal math, pruned denominators, and forbidden cells as runtime checks.
Managing Cross Explosion	Taming a 2048-cell product down to a closable 30-cell goal.
Cross Coverage Patterns	Four reusable patterns and a spec-table-to-cross transcription.

Check yourself Both coverpoints read 100%, but the cross reads 60%. Is the cross automatically covered?

No. Per-point 100% proves each value occurred in some sample, not that the combinations occurred in the same sample. The cross measures combinations, so per-point closure never implies cross closure.

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