[link Point to another website Only the registered members can access]
Table of Contents
1. INTRODUCTION...................................... .................................................. ...................................7
1.1. BACKGROUND........................................ .................................................. ...................................7
1.2. PROBLEM DESCRIPTION....................................... .................................................. ......................7
1.2.1. Method............................................ .................................................. ...............................7
1.3. STRUCTURE OF THE REPORT............................................ .................................................. .........8
2. CONCEPTS AND DEFINITIONS....................................... .................................................. ....9
2.1. THE SAFETY-CRITICAL SYSTEM DEFINITION........................................ ....................................9
2.2. THE ERROR PROPAGATION CONCEPT........................................... ...............................................9
2.3. THE ERROR CONTAINMENT CONCEPT........................................... ............................................10
2.3.1. Fault avoidance......................................... .................................................. ................10
2.3.2. Fault detection/verification...................................... ...............................................10
2.3.3. Fault tolerance/fail safe.............................................. .............................................11
2.3.4. Fault removal........................................... .................................................. ..................11
2.4. DEFINITIONS, ACRONYMS AND ABBREVIATIONS USED IN THIS PAPER................................12
3. LITERATURE SURVEY............................................ .................................................. ................14
3.1. THE SEARCH............................................ .................................................. ................................14
3.2. SHORT SUMMARY OF SURVEYED PAPERS............................................ .....................................14
3.3. CONCLUSIONS FROM THE SURVEY............................................ ................................................16
4. PROPAGATION ANALYSIS.......................................... .................................................. ........17
4.1. MODEL BASED PROPAGATION ANALYSIS.......................................... ........................................17
5. MODELLING TECHNIQUES AS A BASIS FOR ERROR PROPAGATION ANALYSIS.......................................... .................................................. .................................................. 18
5.1. THE DIRECTED GRAPH MODEL............................................. .................................................. ...18
5.2. SEQUENCE DIAGRAMS.......................................... .................................................. ..................21
5.3. STIMULUS RESPONSE MODELS............................................ .................................................. ...22
6. ANALYSIS METHODS APPLIED TO FUNCTIONAL SYSTEM MODELS.............25
6.1. ERROR PERMEABILITY ANALYSIS.......................................... .................................................. ..25
6.1.1. Obtaining Numerical Estimates of Error Permeability..................................29
6.2. ERROR PATH ANALYSIS.......................................... .................................................. .................29
6.3. FAILURE MODE EFFECT ANALYSIS (FMEA)............................................ .................................30
7. METHODS FOR FINDING AND RESOLVING ERROR PROPAGATION.............31
7.1. SOFTWARE TESTING........................................... .................................................. .....................31
7.2. RECOVERY TECHNIQUES........................................ .................................................. ..................32
7.3. WHICH MODULES TO CONSIDER?......................................... .................................................. .32
8. TYPES OF MULTITASKING OPERATING SYSTEMS........................................... .......34
8.1. TYPES OF SYSTEMS........................................... .................................................. .......................34
9. ERROR PROPAGATION IN THE C PROGRAMMING LANGUAGE........................35
9.1. HISTORY OF C................................................. .................................................. ........................36
9.2. PITFALLS AND TRAPS IN C................................................. .................................................. .....36
9.2.1. Lexical errors............................................ .................................................. .................36
9.2.2. The switch statement......................................... .................................................. ....39
- 3 - Safety in programmable systems Error propagation
9.2.3. Multitasking...................................... .................................................. ..........................40
9.2.4. Global variables......................................... .................................................. ...............41
9.2.5. Pointers and arrays............................................ .................................................. .....42
9.2.6. Casting........................................... .................................................. .............................43
9.2.7. The goto statement......................................... .................................................. ........43
9.2.8. The if and else statement......................................... ..............................................44
9.2.9. Integer overflow.......................................... .................................................. .............45
9.2.10. Dynamic allocation........................................ .................................................. ......45
9.3. TYPES OF ERROR PROPAGATION MECHANISMS IN THE C PROGRAMMING LANGUAGE...........46
9.3.1. Intended communication..................................... .................................................. ..46
9.3.1.1. Function call.............................................. .................................................. .............49
9.3.1.2. Global variables......................................... .................................................. ...........51
9.3.1.3. Sharing of common data storage........................................... .........................53
9.3.2. Unintended communication..................................... ...............................................53
9.3.2.1. Sharing of memory............................................ .................................................. .53
9.3.3. Denial of resource.......................................... .................................................. ..........54
9.3.3.1. Allocation of memory............................................ ...............................................54
9.3.3.2. Sharing of CPU............................................... .................................................. ......56
9.3.3.3. Sharing of input/output devices........................................... ...........................56
10. PRACTICAL USE............................................... .................................................. ....................57
10.1. AN INTRODUCTION TO AASV (AIR BASED PART)............................................. .................58
10.2. DIRECTED GRAPH............................................. .................................................. ...................61
10.3. A CLOSER ANALYSIS OF THE SYSTEM............................................ ......................................64
10.3.1. Scenario 1 (I1 to O1)............................................... ............................................64
10.3.1.1. Sequence Diagram (SD).............................................. .......................................64
10.3.1.2. Error path analysis.......................................... .................................................. ....65
10.3.1.3. Comment........................................... .................................................. .....................65
10.3.2. Scenario 2 (I2 to O1)............................................... ............................................65
10.3.2.1. Sequence Diagram (SD).............................................. .......................................65
10.3.2.2. Error path analysis.......................................... .................................................. ....66
10.3.2.3. Comment........................................... .................................................. .....................66
10.3.3. Function – main()............................................ .................................................. ....66
10.3.3.1. Stimulus Response Model............................................. ......................................67
10.3.3.2. FMEA.............................................. .................................................. ...........................68
10.3.3.3. Comment........................................... .................................................. .....................69
10.3.4. Function – RecieveGSMData().................................. ........................................69
10.3.4.1. Stimulus Response Model............................................. ......................................70
10.3.4.2. FMEA.............................................. .................................................. ...........................71
10.3.4.3. Comment........................................... .................................................. .....................74
10.3.5. Function – tokenizeInput()................................... .............................................74
10.3.5.1. Stimulus Response Model (part1)........................................... ........................75
10.3.5.2. Stimulus Response Model (part 2)................................................ ..................76
10.3.5.3. FMEA.............................................. .................................................. ...........................77
10.3.5.4. Comment........................................... .................................................. .....................85
10.3.6. Function – setServoPositions()............................... ..........................................85
10.3.6.1. Stimulus Response Model............................................. ......................................86
10.3.6.2. FMEA.............................................. .................................................. ...........................87
10.3.6.3. Comment........................................... .................................................. .....................88
10.3.7. Function – RecieveGPSData().................................. .........................................88
10.3.7.1. Stimulus Response Model............................................. ......................................89
10.3.7.2. FMEA.............................................. .................................................. ...........................90
- 4 - Safety in programmable systems Error propagation
10.3.7.3. Comment........................................... .................................................. .....................92
10.3.8. Function – nmeaFilter()...................................... ................................................92
10.3.8.1. Stimulus Response Model............................................. ......................................93
10.3.8.2. FMEA.............................................. .................................................. ...........................94
10.3.8.3. Comment........................................... .................................................. .....................98
10.3.9. Function – autonomous()...................................... .............................................98
10.3.9.1. Stimulus Response Model (part 1)................................................ ..................99
10.3.9.2. Stimulus Response Model (part 2)................................................ ................100
10.3.9.3. FMEA.............................................. .................................................. .........................101
10.3.9.4. Comment........................................... .................................................. ...................104
10.3.10. Function – Calc_Bearing().................................... ............................................104
10.3.10.1. Stimulus Response Model............................................. ...............................105
10.3.10.2. FMEA.............................................. .................................................. ....................106
10.3.10.3. Comment........................................... .................................................. ..............107
10.3.11. Function – Convert_GPS2deg()................................. ....................................107
10.3.11.1. Stimulus Response Model............................................. ...............................107
10.3.11.2. FMEA.............................................. .................................................. ....................107
10.3.11.3. Comment........................................... .................................................. ..............108
10.3.12. Function – Convert_deg2rad()................................. ......................................108
10.3.12.1. Stimulus Response Model............................................. ...............................108
10.3.12.2. FMEA.............................................. .................................................. ....................108
10.3.12.3. Comment........................................... .................................................. ..............108
10.3.13. Function – Convert_rad2deg()................................. ......................................108
10.3.13.1. Stimulus Response Model............................................. ...............................109
10.3.13.2. FMEA.............................................. .................................................. ....................109
10.3.13.3. Comment........................................... .................................................. ..............109
10.4. SUMMING UP................................................ .................................................. .....................109
11. SUMMARY AND CONCLUSION........................................ .............................................111
11.1. PURPOSE........................................... .................................................. ................................111
11.2. ERROR PROPAGATION MECHANISMS........................................ .........................................111
11.2.1. Intended communication..................................... .............................................112
11.2.2. Unintended communication..................................... ........................................112
11.2.3. Denial of resources......................................... .................................................. ..112
11.3. MODELLING TECHNIQUES AS BASIS FOR ERROR PROPAGATION ANALYSIS....................112
11.3.1. The direct graph model............................................. ........................................112
11.3.2. Message Sequence Charts/Sequence Diagram........................................112
11.3.3. Stimulus response models............................................ ...................................113
11.4. ANALYSIS METHODS........................................... .................................................. ..............113
11.4.1. Error path analysis.......................................... .................................................. ..113
11.4.2. Failure modes and effects analysis.......................................... .....................113
11.5. COMBINATIONS OF THE DIFFERENT TECHNIQUES AND METHODS...................................114
11.5.1. The modelling techniques........................................ .........................................114
11.5.2. The analysis methods........................................... .............................................115
11.6. THE C LANGUAGE AND ERROR PROPAGATION....................................... ...........................115
11.7. SUMMING UP................................................ .................................................. .....................115
12. FURTHER WORK.............................................. .................................................. ..................116
12.1. AUTOMATION........................................ .................................................. ............................116
12.2. COMPARING OPERATING SYSTEMS........................................... .........................................117
INDEX............................................. .................................................. .................................................. ...118
- 5 - Safety in programmable systems Error propagation
13. REFERENCES........................................ .................................................. ...............................121
APPENDIX A (SOURCE CODE)............................................. .................................................. .....123
-
Reply With Quote
Bookmarks