Understanding Coverage Metrics

There are different types of coverage.

1. Test or Scenario Coverage. It is a simple PASS/FAIl metric telling you if a specific simulation (test/schenario) was successfull.
2. Code Coverage. Originally in the digital world.. This metric tells you about the completeness of your test. It tells you what part of the (digital) code was exercised. As such, it is implementation-dependant. The code coverage is generally split into several "sub-metrics" : block/line, expression, toggle, plus two specific metrics related to Finite State Machine (FSM) coverage : the state and the arcs reached. It does not need any specific coding efforts.
3. Functional Coverage. The Functional Coverage was mainly introduced by VERA (from Synopsys), Specman/e (from Cadence) and PSL/Sugar from IBM.It has then been introduced into SystemVerilog. It is meant to track which functionality of the SoC was exercised.It does not depend on the implementation. It does need some extra coding and is closely linked to the specification and the Verification Plan. The Functional Coverage is commonly split into two categories : control-oriented and data-oriented. The control-oriented Functional Coverage defines SoC's properties which are then checked (asserted). These assertions can be immediate or concurrent (sequences). Systemverilog provides specific operators to specify sequences. The data-oriented Functional Coverage tracks the number of times a design variable reaches a specified set of values or value-transitions.