How safe is your software?

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Jeffery Reynard Burns
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1 Presentation Bio Return to Main Menu P R E S E N T A T I O N T4 Thursday, Dec 7, 2000 How safe is your software? Johan Hedberg International Conference On Software Testing, Analysis & Review DEC 4-8, 2000 COPENHAGEN, DENMARK

2 How safe is your software? Johan Hedberg, SP Lars Strandén, SP SP Swedish National Testing and Research Institute 1

3 PALBUS Swedish joint research project between Industry, University and Research Institutes How to design dependable distributed control systems How to validate/verify systems to reach dependability Present useful methods for validation/verification 2

distributed control systems How to validate/verify systems to

4 Background Trend with increased use of distributed control systems in safety critical applications Important to achieve a certain level of dependability in such systems Increased industry interest concerning dependability Combine knowledge and experience from Industry, University and Institutes 3

dependability in such systems Increased industry interest concerning

5 Background, cont. Started in August 1999 and will end in April 2001 Totally 14 different work packages 4

6 Application domain System Distributed control system Safety Embedded system Real-time Software/hardware interaction 5

7 System overview Overview of the distributed system inparameter_node1 inparameter_node2 outparameter_node1 * Adjustment of format Filtering Calculation outtparameter_node2 Calculation Filtering Adjustment of format Protocol generator / Protocol degenerator Protocol generator / Protocol degenerator Adjustment of format Filtering Calculation * Calculation Filtering Adjustment of format Common communication bus Adjustment of format Filtering Calculation * Calculation Filtering Adjustment of format Protocol generator / Protocol degenerator Protocol generator / Protocol degenerato Adjustment of format Filtering Calculation Calculation Filtering Adjustment of format * inparameter_node4 outparameter_node4 outparameter_node3 inparameter_node3 6

Adjustment of format Common communication bus Adjustment of format Filtering Calculation * Calculation Filtering Adjustment of format Protocol generator / Protocol degenerator Protocol

8 Definitions & standards According to Laprie s definitions Dependability - availability - reliability - safety - security Relevant standards Adjudged or hypothesized cause... FAILURE FAULT ERROR FAILURE FAULT... Activation (internal) Occurrence (external) Fault - fault, bug, defect, mistake, et c System internal effect Deviation of delivered service from compliance to system specification User perceived effect Failure - failure, crash, breakdown, malfunction, denial of service, et c 7

.. Activation (internal) Occurrence (external) Fault - fault, bug, defect, mistake, et c System internal effect Deviation

9 New types of errors Node error Bus error Timing error Data consistency error Initialization & restart error Babbling idiot error Configuration error Node A Node B Node C Node D 8

10 New types of errors, cont. New error types require new fault detection and fault handling methods The distribution of computing gives new ways to detect and handle faults 9

11 Time triggered/event triggered Bus access techniques Delay Jitter Scheduling Fault detection and fault handling Acceptance How do the protocols handle errors related to distributed systems? 10

12 Bus access techniques Bit wise arbitration mechanism: Each nodes sending timeslot in a time triggered protocol node 1 node 2 node3 node1 node2 node3 node4 node1 node2 node3 node increasing time Communication bus 11

node 2 node3 node1 node2 node3 node4 node1 node2 node3 node4

13 Design principles for dependable systems Focus on design principles specific for distributed control systems Utilize the protocol optimally to reach as high dependability as possible How to improve the performance of the protocol 12

Utilize the protocol optimally to reach as high

14 Validation & verification methods Focused on methods related to the distribution Divided into the following groups: - formal methods - analysis - test - trial - simulation 13

15 Fault tree applied to distributed control systems Safety related failure in the system > System level > Application level Failures related to the distribution of nodes > Communic ation controler level EMC > > > Bus level Failure in hardware Vibra > Humi dity Temp Implementation of software do not fulfill the specification Failure in software > Specification has not considered all possible risks 14

level EMC > > > Bus level Failure in hardware Vibra > Humi dity Temp Implementation of software do

16 Structure of a distributed control system What do we mean with system aspects? All levels must be considered to reach dependability System Application Communication controller Bus 15

17 Prototype system CAN based system Available for all participants in the project Used by the participants to be able to analyze and test ideas and methods developed in the project 16

18 Applying analysis & test methods Application dependent Practical implementation of analysis methods described in the project Quality of developed methods New methods 17

19 Trends Increased system complexity More frequent use of COTS Less embedded systems Higher dependability demands 18

20 Conclusions Distributed control systems give new possibilities to supervise the behaviour of the application Decide, as early as possible, if a distributed architecture should be used in the development phase Present validation/verification methods to handle software related errors in distributed control systems Indicate a certain level of dependability in software by using methods developed in the PALBUS project 19

development phase Present validation/verification methods to handle software related errors in

21 PALBUS information PALBUS results are available at the following address: 20

22 Thursday 7 December 2000 T4 How safe is your software? Johan Hedberg Johan Hedberg received his Master of Science in Electrical Engineering 1999 from Chalmers University of Technology in Gothenburg, Sweden. His thesis work named Implementation of a Distributed Control Application Based on the TTP/C Architecture was performed at Volvo Technological Development. At SP he has continued to work with distributed systems in a research project financed by NUTEK (The Swedish National Board for Industrial and Technical Development). The purpose of this project is to find out methods to evaluate dependability of distributed control systems. He is working at the SP section of Software & Safety. Lars Strandén received his Master of Engineering Physics 1976 from University of Technology in Uppsala, Sweden. He has worked with real-time embedded systems and large radar applications written in Ada at Ericsson Microwave Systems. He worked as a technical specialist concerning software development methods and received his Licentiate of Engineering 1998 from Chalmers University of Technology in Gothenburg, Sweden. After that he has worked two years as a computer system consultant and works now at SP section Software & Safety. His interests are focused around dependable software within real-time embedded applications and he is currently involved in a research project concerning dependability together with a number of companies and Chalmers University of Technology.

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