IBM Haifa Research Lab

© 2006 IBM Corporation© 2007 IBM Corporation

A Framework for the Validation of Processor Architecture Compliance

Allon Adir, Sigal Asaf, Laurent Fournier, Itai Jaeger(*), Ofer Peled

2

Processor architecture licensing

Commercial processor architecture licensing drives the need for compliance validation

– Architecture owners must prevent fragmentation of the architecture

– Licensees would like to make sure their design is compatible with existing facilities and software

IBM Labs in Haifa

3

Implementation=~?

Designer’s intent=~?

Architecture compliance validation

Architecture

Functional verificationCompliance validation

Verify that:Designers have interpreted the architecture correctlyArchitecture prescriptions have been followed in a consistent manner

3

4

Human interaction based processes

– Error prone

– Expert effort needed

Legacy architecture compliance test suite

– Not systematic

– Maintenance issuesWhen does ‘add’ instruction set the CR bit to zero ?

The problem – cont’

Developing an Architecture Validation Suite Application to the PowerPC Architecture (Fournier et al., DAC ’99)

• Based on a static set of testcases

• Covering several ad-hoc coverage models

Methods for architecture compliance validation

5

Provide a comprehensive set of test cases

– Covering each and every aspect of the architecture

Make deviation from the architecture observable

– Create tests that distinguish wrong behavior from right behavior

Enable easy maintenance

– Support different implementations of the same architecture

– Effectively cope with architecture evolution

Compliance validation challenges

6

Back-up pages: The detailed solution ACS – an automatic compliance suite generator

-

Generator

Test Specification

Test Specification Generator

PowerPCReference Model

PowerPCKnowledge Base

Design Specificknowledge Base Architectural

Design SpecificReference Model

Architectural

Design Specific Coverage Models

Model-basedTest Generator

Test Specification

Test Specification

Test Specification Generator

PowerPCReference Model

PowerPCKnowledge Base

ArchitecturalKnowledge Base

ArchitecturalReference Model

Architectural Coverage Models

Compliance Test Cases

7

ACS coverage models Misinterpretation based coverage models

– Ambiguity in the text

– Oversight of specification portions

– Subconscious confusion with a similar, yet different, specification

• Internal or external association

Automatically derived from description of

– Single instruction behavior

– Architectural mechanisms (e.g., translation, interrupts)

– Synchronization and multi-processor requirements

8

Implementation decisions It is common for processor architecture to allow several alternative

legal behaviors

– Implement vectored instructions?

– Take an interrupt on overflow?

A single test may be legal for one implementation of the architecture but illegal for another…

Not all coverage models are applicable to every implementation of the architecture

9

The complete ACS system

Compliance Test Cases

Generator

TestSpecification

ACS Defs Generator

Architecture Decisions

ArchitecturalCoverage Models

Architectural Reference Model

ArchitecturalKnowledge Base

1) fsel implemented yes

2) External control facility yes

3) Memory size 2^52…

Model-based Test Generator

10

Summary

The need for architecture compliance validation is growing

– Architecture licensing business models

Complex and evolving architectures pose significant challenges

– Current methods are not complete and robust enough

ACS – a system for automatically generating compliance test suites

– Comprehensive coverage of misinterpretation models

– Automatic generation according to specific implementation choices

– Model-based approach addresses architecture evolution

IBM Haifa Research Lab

© 2006 IBM Corporation© 2007 IBM Corporation

Thank you

12

Backup

13

OE=1

setOverflow = False setOverflow = True

Mode = 64-bit Mode = 32-bit

64_overflow_occurred = true

Misinterpretation flowchart coverage models

prec=64 prec=32

OE = 0 OE = 1

OE=0 OE=1

OE=0

64_overflow_occurred = false

OE=0

32_overflow_occurred = false

OE=1

32_overflow_occurred = true

Misinterpretation task: The process goes down a false edge instead of the right edge coming out of the same node

14

Misinterpretations

The concept of misinterpretation constitutes the backbone of the ACS coverage models

Causes for misinterpretations

– Ambiguity in the text

– Oversight of specification portions

– Subconscious confusion with a similar, yet different, specification

• Internal association• External association

5/0=

Arch. Overflow interrupt

Divide by zero interrupt

15

ACS coverage models The coverage models target misinterpretations of

– Single instruction behavior

– Architectural mechanisms (e.g., translation, interrupts)

– Synchronization and multi-processor requirements

Two types of coverage models are supported:

– Flowchart based models

– Cross product models

CR[0:2] = unchanged

CR[0:2] = 0b001 CR[0:2] = 0b010 CR[0:2] = 0b100

Inst.isRecord=falseInst.isRecord=true

MSR[SF] = 0MSR[SF] = 1

faddfdivfmul

Instruction

+Zero-Zero

+Number-Number

+Inf-InfNan

Operand1 Operand2

+Zero-Zero

+Number-Number

+Inf-Infnan