coverpoints

Coverpoints are a core concept in functional coverage for digital design verification. A coverpoint represents a specific signal, variable, or expression whose observed values during simulation are of interest. The goal of capturing coverpoints is to quantify how thoroughly the stimulus exercises the design and to reveal coverage gaps that tests have not hit.

Coverpoints are defined inside a covergroup, and each coverpoint collects samples from its expression. The samples are organized into bins, which can be value bins, range bins, or enumerated sets. By creating bins that reflect design-relevant scenarios, the verification engineer can measure how often particular conditions occur. Cross constructs enable the measurement of coverage for combinations of multiple coverpoints, increasing the ability to detect gaps where certain interactions never happen.

In practice, a covergroup may include a coverpoint for an opcode with bins such as 0–3, 4–7, and others; a coverpoint for a valid signal with bins for 0 and 1; and a cross between opcode and the valid signal to observe which opcodes occur when valid is asserted. The tool reports coverage as a percentage of bins hit, along with hit counts for individual bins.

Best practices include aligning coverpoints with functional requirements, using meaningful and well-spaced bins, avoiding excessive granularity, and using crosses to exercise interaction effects. Coverage analysis should complement other verification metrics, as high coverage does not guarantee correctness and may require maintenance as the design evolves.

See also: SystemVerilog, functional coverage, covergroup, coverpoint, UVM.