Formal Verification Applied to Attitude Control Software of Unmanned Aerial Vehicles

113 Pages·2017·2.68 MB·English

Universidade Federal do Amazonas
Faculdade de Tecnologia
Programa de Pós-Graduação em Engenharia Elétrica
Formal Verification Applied to Attitude Control
Software of Unmanned Aerial Vehicles
Lennon Corrêa Chaves
Manaus–Amazonas
Fevereirode2018
Lennon Corrêa Chaves
Formal Verification Applied to Attitude Control
Software of Unmanned Aerial Vehicles
Dissertação apresentada ao Programa de Pós-
Graduação em Engenharia Elétrica, como requi-
sito parcial para obtenção do Título de Mestre
em Engenharia Elétrica. Área de concentração:
AutomaçãoeControle.
Orientador: Prof. Dr. LucasCarvalhoCordeiro
Coorientador: Prof. Dr. EddieBatistadeLimaFilho
Lennon Corrêa Chaves
Formal Verification Applied to Attitude Control
Software of Unmanned Aerial Vehicles
BancaExaminadora
Prof. D.Sc. EddieBatistadeLimaFilho–PresidenteeOrientador
DepartamentodeEletrônicaeComputação–UFAM
Prof. D.Sc. WaldirSabinodaSilvaJunior
DepartamentodeEletrônicaeComputação–UFAM
Prof. D.Sc. JoséReginaldoHughesCarvalho
InstitutodeComputação–UFAM
Manaus–Amazonas
Fevereirode2018
Ficha Catalográfica
Ficha catalográfica elaborada automaticamente de acordo com os dados fornecidos pelo(a) autor(a).
Chaves, Lennon Corrêa
C512f Formal Verification Applied to Attitude Control Software of
Unmanned Aerial Vehicles / Lennon Corrêa Chaves. 2018
94 f.: il. color; 31 cm.
Orientador: Lucas Carvalho Cordeiro
Coorientador: Eddie Batista de Lima Filho
Dissertação (Mestrado em Engenharia Elétrica) - Universidade
Federal do Amazonas.
1. Unmanned Aerial Vehicle. 2. Symbolic Model Checking. 3.
Fixed-Point Digital Controllers. 4. Embedded Systems. I. Cordeiro,
Lucas Carvalho II. Universidade Federal do Amazonas III. Título
Tomyparents...
Acknowledgements
I would like to thank my supervisor Dr. Cordeiro for his support, guidance, encourage-
ment and friendship during the last two years. I believe that his support helped me to become
a better professional and researcher through the M.Sc. dissertation. You have set an example
of excellence as a researcher, mentor, instructor, and role model. Thanks for giving me the
opportunitytobepartofyourresearchgroup.
I would also like to thank my co-supervisor Dr. Lima Filho for being a professor who
encouraged me always to develop my work with high quality, giving me excellents feedbacks
toalwaysimproveasresearcher.
Many thanks to my friends and colleagues from UFAM to help me with their contribu-
tionsinmyresearchandclasses,andforalwaysencouragedmetonotgiveupduringhardtimes
anddoallmybestinanysituation. ThankyouAnne,Alay,MykeandFelipe.
I would also like to thank my friends Lauana and Mauricio, for being the friends that I
neededtohaveinmylife. Thanksforthefunmomentsandforinspiringmetodomybest.
I would especially like to thank my family for the love, support, and constant encour-
agement I have gotten over the years. In particular, I would like to thank my parents for their
support in my education and because they never stopped to believe in me. I dedicate this dis-
sertationtothem.
“IsolemnlyswearthatIamuptonogood.”
J.K.Rowling,HarryPotterandThePrisonerofAzkaban
Abstract
Duringthelastdecades,modelcheckingtechniqueshavebeenappliedtoimproveover-
allsystemreliability,inunmannedaerialvehicle(UAV)approaches. Nonetheless,thereislittle
effort focused on applying those methods to the control-system domain, especially when it
comes to the investigation of low-level implementation errors, which are related to digital con-
trollers and hardware compatibility. The present study addresses the mentioned problems and
proposes the application of a bounded model checking tool, named as Digital System Verifier
(DSVerifier), to the verification of digital-system implementation issues, in order to investigate
problems that emerge in digital controllers designed for UAV attitude systems. A verification
methodology to search for implementation errors related to finite word-length effects ( e.g.,
arithmetic overflows and limit cycles), in UAV attitude controllers, is presented, along with its
evaluation, which aims to ensure correct-by-design systems. Experimental results show that
failuresinUAVattitudecontrolsoftwareusedinaerialsurveillance,whicharehardlyfoundby
simulationandtestingtools,canbeeasilyidentifiedbyDSVerifier.
Keywords: Unmanned Aerial Vehicle, Symbolic Model Checking, Fixed-Point Digital Con-
trollers,EmbeddedSystems.
Resumo
Duranteasúltimasdécadas,técnicasdeverificaçãodemodelostemsidoutilizadaspara
melhorar a confiabilidade de sistemas, no que diz respeito a veículos aéreos não-tripulados
(VANTs). Contudo, existem poucos esforços focados em aplicar esses métodos ao controle de
sistemas, especialmente os relativos à investigação de erros de implementação de baixo nível,
os quais estão relacionados a controladores digitais e compatibilidade de hardware. O presente
trabalho aborda os problemas mencionados e propõe a aplicação de uma ferramenta de verifi-
caçãolimitadademodelos,conhecidacomoDigitalSystemVerifier(DSVerifier)ouVerificador
deSistemasDigitais,àverificaçãodeimplementaçãodesistemasdigiais,comoobjetivodein-
vestigar problemas em controladores digitais projetados para sistemas de atitude em VANTs.
Apresenta-se uma metodologia de verificação para procurar por erros de implementação rela-
cionados a efeitos de tamanho de palavra finita (i.e, estouros aritméticos e ciclos-limites), em
controladores de atitude de VANTs, juntamente com sua avaliação, o que visa garantir a corre-
tudedessessistemas. Resultadosexperimentaismostramquefalhasencontradasemsoftwarede
controledeatitudedeVANTsusadosemvigilânciaaérea,asquaissãodificilmenteencontradas
prosimulaçãoeferramentasdeteste,podemserfacilmenteidentificadaspeloDSVerifier.
Palavras-Chave: Veículos Aéreos Não Tripulados, Verificação Símbolica de Modelos, Contro-
ladoresdePonto-Fixo,SistemasEmbarcados.
Contents
ListofFigures xiv
ListofTables xvi
ListofAlgorithms xvii
Acronyms xviii
1 Introduction 1
1.1 ProblemDescription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 OrganizationoftheDissertation . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Background 5
2.1 DigitalControllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Direct-FormRealizations . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Fixed-PointRepresentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Fixed-PointArithmetics . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Fixed-PointImplementationinUAVsControllers . . . . . . . . . . . . 7
2.3 ProblemsRelatedtoFixed-PointImplementations . . . . . . . . . . . . . . . . 8
2.3.1 Round-offEffectandPolesandZerosSensitivity . . . . . . . . . . . . 10
2.3.2 ArithmeticOverflow . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.3 LimitCycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.4 Samplingeffect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 SatisfiabilityModuloTheories . . . . . . . . . . . . . . . . . . . . . . . . . . 12
x