Cadence has created a unique and innovative plan- and coverage-based solution for tracking and signoff of top-level requirements, where requirements to test case traceability are now mandated in several industries. The single biggest challenge identified by most users is the need to trace a requirement through all of its the various transformations, eventually to a set of tests that satisfy those requirements. While standards vary somewhat from industry to industry, this test-case traceability aspect is the key element of any requirements management-flow solution. While traceability does not necessarily need to be automated, according to the experts it is the only practical way to achieve certification. Table 1 lists just some of the industries and the associated international standards that silicon suppliers are mandated to support.
Table 1. Industry Standards mandating requirements traceability
The fundamental capability common to all of the standards above is that you must be able to prove both that the testing done has satisfied a particular requirement and that the test process is viable and comprehensive enough to establish proof. Most silicon projects have tens to hundreds of requirements, which are represented by thousands of sub-features and functions that must be exercised together to accommodate the requirement(s). Each sub-feature and function is functionally tested and hundreds of functional coverage metrics are used to collect results of each test. While some of the requirements are safety related and need additional testing for safety integrity, this process of test definition, to feature/function decomposition, to exercising the critical aspects, and finally to results collection is a well-documented and codified process, implemented by hundreds of Cadence customers.
The only proven way to automate this process is to use a verification planning and management solution, which can manage the complex verification flow including the functional interdependencies and the many-to-many mapping techniques necessary. A requirements management flow solution is nothing more than a few enhancements on top of a proven functional testing process, something the Cadence® Incisive® Verification Platform has been doing for years. The key aspect that Cadence brings is a planning technology explicitly designed for this kind of work.
The highest level of the requirements management flow can be seen in Figure 1. The diagram shows an outer loop of requirements managed by the Incisive Enterprise Manager, and an inner loop run by the Incisive Enterprise Simulator that exhaustively exercises those requirements and returns test results.
Figure 1. The requirements management flow
As with most hardware or software development, no matter how simple the diagram appears, the challenge is in the application and automation of the flow, and ensuring integrity of the testing process and rollup of results. In addition, because most developments are iterative, a well-defined change management process is needed to ensure the development process can operate smoothly.
A comprehensive solution for any of the industries cited in Table 1 should include the following characteristics:
- Qualification of the tool flow
- Qualification and documentation of the functional testing process, often necessary to be validated by an outside approval agency
- Documentation and audit process including bugs, errors, changes, update process, and revision control process
- Implementation of advanced functional verification
- Deterministic methodology supporting functional testing and metrics collection
- Mechanism to roll-up metric results from different levels (unit, sub-system, system), as well as technologies (hardware, software, analog, etc.)
- Traceability automation
- Must be able to trace a requirement through all refinements and through implementation, verification, and final results
- Critical to separately track safety requirements, and to provide a mechanism to trace it to implementation and verification
- Safety testing for faults
- Stuck-at-fault models are the minimal safety requirements
- Must model transient faults induced by radiation
- Fault models needed at different abstraction levels
The Incisive requirements management flow solution is based on the advanced planning capabilities of Incisive Enterprise Manager, which ensures the traceability, testing, management, and execution on various engines (primarily RTL simulation but also software simulation), and the implementation of functional coverage that gets executed within Incisive. The Incisive solution has been used in production in each of the industries listed in Table 1, and Incisive Enterprise Manager was the planning and management solution utilized for the world’s first ISO 26262-certified chip.
The Incisive solution supports the first three required characteristics, with key elements of the solution flow, including:
Electronically link top-level requirements to features—either safety or non-safety based. For each of the key features, you plan how to execute tests for those features and link them together into a comprehensive and executable verification plan (vPlan). The vPlan technology is a living representation of all features and sub-functions, with back-annotated test results.
The verification plan supports all leaf-level details from requirements, to features, to functions, to the coverage elements and metrics. When tests execute, coverage results are populated to each mapped area within their source hierarchy for easier management. A resultant vPlan is the implementation traceability matrix, and is correct by construction, but also serves as the roll-up mechanism for reporting.
Functional coverage is the only metric that pertains to a requirements management flow. Functional metrics can be driven by cover groups or by assertions defined in the testbench, in either hardware or software. Users have a choice of SystemVerilog, Specman e
, PSL, or SVA assertions to define the testbench that drives the test process.
The design and/or requirements specification can be connected to the executable verification plan to ensure test case coverage (each requirement is satisfied by at least one test), and for proposes of specification traceability and change management.
Each section of the verification plan enables specification sections to also be linked, such that any change in requirement, specification, or missing tests can be automatically flagged for user correction.
For more information about the Incisive Requirements Management flow, see the webinar "Integrating Chip Verification into an ISO 26262 Traceability Flow