Bins: Explicit, Auto, Illegal & Ignore · SystemVerilog

Part 5 of 9Functional CoverageIntermediate

4topics
4lessons

A coverpoint names what is watched. Its bins decide which sampled values count as which scenario, which values are violations, and which values are out of scope.

Bin kind	It says	Coverage goal
`bins name = {values}`	This scenario must happen	In
`bins name[] = {...}`	Each of these must happen	In, one bin per value
`bins name = (A => B)`	This sequence must happen	In
`bins other = default`	Anything else, for bookkeeping	Out
`ignore_bins`	Out of scope, do not count	Removed
`illegal_bins`	Must never happen	Removed; a hit is a run-time error
`wildcard bins = {pattern}`	Values matching the pattern	In
`bins ... with (expr)`	Values where the expression holds	In

Coverage is hit goal bins divided by total goal bins.

Lesson	Path	What it covers
Auto Bins vs Explicit Bins	Required	The 64-bucket trap, named value bins, and one bin versus many.
Transition Bins	Recommended	Sequences, repetition operators, and the FSM arc recipe.
Exclusions, Patterns & Filters	Required	Illegal and ignore bins, wildcard patterns, and with filters.
Bin Design Strategy	Recommended	Intent-driven bins, explosion control, and a worked redesign.

Required is the core first pass. Recommended is for most learners. Optional is reference, a specialist topic or revision.

Check yourself A coverpoint declares 8 single-value bins m[] = {[0:7]}, with ignore_bins {6} and illegal_bins {7}. Four goal bins are hit. What is the coverage?

Four of six, 66.7%. Each excluded value was the only value of its bin, so both bins empty out and leave the goal: the denominator is 6, not 8. An exclusion removes a bin only when it empties it.

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Bin kind

It says

Coverage goal

bins name = {values}

This scenario must happen

bins name[] = {...}

Each of these must happen

In, one bin per value

bins name = (A => B)

This sequence must happen

bins other = default

Anything else, for bookkeeping

Out

ignore_bins

Out of scope, do not count

Removed

illegal_bins

Must never happen

Removed; a hit is a run-time error

wildcard bins = {pattern}

Values matching the pattern

bins ... with (expr)

Values where the expression holds

Lesson

Path

What it covers

Auto Bins vs Explicit Bins

Required

The 64-bucket trap, named value bins, and one bin versus many.

Transition Bins

Recommended

Sequences, repetition operators, and the FSM arc recipe.

Exclusions, Patterns & Filters

Required

Illegal and ignore bins, wildcard patterns, and with filters.

Bin Design Strategy

Recommended

Intent-driven bins, explosion control, and a worked redesign.