Combining Code Coverage and FSM Graph in Riviera-PRO to extract FSM debug information

Introduction

The following solution shows how to use code coverage and FSM Graph to extract the information to debug FSMs in design.

Code Coverage

Riviera-PRO provides support for various types of code coverage such as statement coverage, branch coverage, path coverage and expression/condition coverage.

To extract FSM debug data, design can combine information from Line, Branch and Expression coverages.

Where

  • Line Coverage - Shows if reset has been executed

  • Branch Coverage - Shows whether all states of an FSM state has been executed

  • Expression Coverage - Shows whether FSM transition between all states (that are achievable) transitions have not been executed

FSM Graph

While code coverage data shows the information about reset, states and FSM transition, still the details about state transition is required to fully debug the FSMs in the design.

FSM graph tool in Riviera-PRO shows the transitions among object states in graphical and tabular format. The object states and transitions are represented by circles and arrows, respectively on the FSM graph. The numbers displayed under the arrows show how many times the specified transitions occurred.

There are four kinds of states that are distinguished on a graph

  • deterministic (denoted by the blue color) - has only one outgoing transition

  • non-deterministic (denoted by the yellow color) - has more than one outgoing transition

  • beginning (denoted by the green color) - has no incoming transitions

  • ending (denoted by the red color) - has no outgoing transitions

Example

  • Consider the example code file fsm.v below,

  • And the testbench file testbench.v below,

  • Compile and simulate this example design using following script in Aldec Riviera-PRO

  • Following image of FSM graph shows the state hit and transition details.

  • The image shows the time instance, next state has been transitioned. And for a complex FSM design, the graph will be shown as below.

  • Along with the above information, coverage reports can be collected using code coverage viewer as shown below.

  • Below figure shows merged report of all the 3 coverage reports.

Conclusion

This application note shows how combining code coverage with FSM graph can help debug FSMs in design.

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