VGS Advanced Topics
This section provides some information about more advanced features of VGS that are sometimes need for model analysis, test vector generation, and failure analysis.
Vector Generation Options
The default vector generation options work in most cases. This section provides a few guidelines for some special situations.
Test vector generation options by default apply to the entire project (all subsystem). The default options can be changed by selecting the properties menu and Vector Generation Tab. Changes can also be applied to an individual subsystem. If there are issues, this is recommended. However, to apply properties to an individual subsystem, the Build Options much be set to Subsystem Level Options.
Extended MCDC Coverage
There is a vector generation option called for Extended MCDC (as opposed to the default of -MCDC which means DO-178B definition of MCDC which we have always suppored) because that is what the concept of coverage of both > and == for each >= operator falls under.
These options are also available from the command line.
The Coverage Analysis report provides a summary of potential problems that have occurred during the compilation process or the vector generation process. The reports are created for each subsystem, but the details failures occur on a DCP basis.
Compiler errors are tautological problems.
Vector generation failures fall into 1 of 6 basic categories.
Categories 1-3 are:
Convergence errors detected BEFORE subsystem references are enabled
- 1. Relational Operator Failure
- 2. Arithmetic Operator Failure
- 3. Arithmetic Exception
Categories 4-5 are:
Convergence errors detected AFTER subsystem references are enabled. Category 4 and 5 failures are higher level failures that result from combinations of category 1-3 failures within the utility subsystem forest leading to an overall failure to find a single good FCP compatible with the constraints of the main system.
- 4. Subsystem forest completely incompatible with initial ground-term-based state space of main system
- 5. One or more FCP's are compatible with initial state space of main system, but no FCP is compatible beyond ground-term-based state space.
Category 6 is:
- 6. Computation failure in the post-condition expression after constraint convergence has completed successfully.