76 Network Packet Header Generation

8/17/2019 76 Network Packet Header Generation

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Network Packet Header Generation UsingGraph Based Techniques combined with

Software Testing Strategies

Sridevi Navulur

Satheesh Parasumanna

Rama Chaganti

© Accellera Systems Initiative 1


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Application Overview• Simulation-based Network Processor Verification presents

unique challenges due to the large number of packet

constructions and requirements to model and measure

those that are legal.



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Motivation & Challenges

• Motivation :

– Simplify generation of complex packet or frame headerinformation and exhaustively test all randompermutations and combinations of legal network protocolheaders.

• Challenges

– Huge space of legal combinations to cover

– Computational expensive simulation cycles

– Cumbersome hand written cover groups and hence nometrics for what has been covered.


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Goals & Main IdeaStimulus Generation Goals & Modeling Approaches tried

Stimulus Generation Goals & Approaches tried Functional Coverage Generation Approaches tried

Rand-sequence:

o Rand-sequence to cover all the

combinations

o Multiple hand-coded tests with different

rand-sequences for path coverage

o No automatic functional coverage

generation support

Hand-coding :

o A huge task in identifying and coding to

cover all the protocols header types

o ~800 lines of hand-written Cover point

code for SV Transition coverage

o Difficult to handle illegal and ignore bins

for SV cover points and cross points

Recursive Graph: Initial solution

Cons :

o Lack of recursion depth control

o No automatic functional coverage

generation support

Graph Based:

o Graph tool supports automatic creation of

pairwise SV cover points & crosses.

o Generates cross of previous header type and

index of next header type

o Automatic generation of previous & next SV

illegal bins restrict solutions to legal subset

Pairwise Graph:

Final solution, addressed recursion issues and

enabled functional coverage generation


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Strategy and Approach


• Uses a Portable Stimulus solver

• Constraint-based stimulus description• Goal-based value generation

• User developed portable stimulus rules

• Analyzes variables for reachability

• Identifies strategy-specific (pair-wise) goals

• Tool creates

• Stimulus-generator class

• Strategy-specific SV cover group

• Why pair-wise testing ?

• Proven approach from the software testing domain

• Strategize to select pairs, triples, quads of variable

to exercise

• Pairwise strategy sufficient for this application

• Pairwise Graph Structure• Previous/Next State options tracked

• Scalable to large sequential headers

• Tool generates SV Coverage classes


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Implementation : Stimulus Generator

Portable Stimulus Rule file


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Implementation of Stimulus


Example Application Rules:

Every Packet in this examplewould start with EthernetHeader and can traversethrough multiple types ofheaders of various

combinations and construct apacket.

Maximum depth of the headertypes can also be changed. Inthis application example welimited the MAX Depth of the

header combinations to be 8 atany given time.

• Portable Stimulus rules syntax

• Rules coverage strategy


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Evidence & Results


# Tests Code Cov Func. Cov Lines of Code Cpu time

12 directed + CR tests 85% none ~1800 Lines 4 hours

1 Portable Stimulus test 94.98% 100% ~220 lines 40 minutes

• Compare Pairwise-driven generation and Rand-Sequence

– Use Ethernet packet – Apply pairwise strategy

• Pairwise-driven stimulus easily hits all cases

• Replace a suite of random+directed tests with 1 portablestimulus test

– 12 directed+CR tests (~1800 lines of code) replacedwith 1 portable stimulus test (220 lines of code)

attaining 95% code coverage and 100% functionalcoverage. Coverage snippet below.


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Conclusion



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Limitation & Future Scope


Limitations : Every time design spec changes, thestimulus rule graph needs to be updated.

Future Scope : Automate the ability to choosevarious rule graphs with respective strategies

References• http://www.xilinx.com/applications/wired-communications/sdnet.html

• http://www.pairwise.org/


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Q&A


76 Network Packet Header Generation

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