VDM-10 Language Manual

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$Course Material\Efficiently Coding Communication Protocols in C++ ...$

VDM-10 Language Manual Figure 16.1: Period (p), jitter (j), delay (d) and offset (o) 2. jitter: This is a non-negative value that describes the amount of time variance that is allowed around a single event. We assume that the interval is balanced [-j, j]. Note that jitter is allowed to be bigger than the period to characterize so-called event bursts. 3. delay: This is a non-negative value smaller than the period which is used to denote the minimum inter arrival distance between two adjacent events. 4. offset: This is a non-negative value which is used to denote the absolute time value at which the first period of the event stream starts. Note that the first event occurs in the interval [offset, offset+ jitter]. Given a defined time resolution ∆T, a thread with a periodic obligation invokes the mentioned operation at the beginning of each time interval with length period. This creates the periodic execution of the operation simulating the discrete equivalent of continuous relations which have to be maintained between instance variables, parameter values and possibly other external values obtained through operation invocations. It is not possible to dynamically change the length of the interval. Periodic obligations are intended to describe e.g. analogue physical relations between values in formulas (e.g. transfer functions) and their discrete event simulation. It is a requirement on the implementation to guarantee that the execution time of the operation is at least smaller than the used periodic time length. If other operations are present the user has to guarantee that the fairness criteria for the invocation of these other operations are maintained by reasoning about the time slices used internally and available for external invocations. A periodic thread is not created or started when an instance of the corresponding class is created. Instead, as with procedural threads, start statements should be used with periodic threads. Examples: Consider a timer class which periodically increments its clock in its own thread. It provides operations for starting, and stopping timing, and reading the current time. ✞ class Timer ✡✝ 146 ✆
Chapter 16. Threads (VDM++ and VDM-RT) The Timer has two instance variables the current time and a flag indicating whether the Timer is active or not (the current time is only incremented if the Timer is active). ✞ instance variables curTime : nat := 0; active : bool := false; ✡✝ ✆ The Timer provides straightforward operations which need no further explanation. ✞ operations public Start : () ==> () Start() == (active := true; curTime := 0); public Stop : () ==> () Stop() == active := false; public GetTime : () ==> nat GetTime() == return curTime; ✡✝ IncTime: () ==> () IncTime() == if active then curTime := curTime + 100; ✆ The Timer’s thread ensures that the current time is incremented. The period with which this is done is 1000 time units. The allowed jitter is 10 time units and the minimal distance between two instances is 200 time units and finally no offset has been used. ✞ thread periodic(1000,10,200,0)(IncTime) end Timer ✡✝ ✆ 147
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Overture - Open-source Tools for Fo
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Contents 1 Introduction 1 1.1 The V
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CONTENTS 13 Statements 97 13.1 Let
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CONTENTS A.7.19 The Undefined Expre
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Chapter 1 Introduction The Vienna D
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Chapter 2 Concrete Syntax Notation
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Chapter 3 Data Type Definitions As
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Chapter 3. Data Type Definitions We
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Chapter 3. Data Type Definitions Op
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Chapter 3. Data Type Definitions (a
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Chapter 4 Algorithm Definitions In
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Chapter 5 Function Definitions In t
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Chapter 5. Function Definitions Not
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Chapter 5. Function Definitions Thi
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Chapter 6 Expressions In this subse
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Chapter 6. Expressions ✡✝ mk_Sc
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Chapter 6. Expressions Examples: Th
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Chapter 6. Expressions where e1 is
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Chapter 6. Expressions all expressi
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Chapter 6. Expressions where bd is
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Chapter 6. Expressions 6.8 Sequence
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Chapter 6. Expressions where all th
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Chapter 6. Expressions mu operator.
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Chapter 6. Expressions new expressi
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Chapter 6. Expressions Examples: Us
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Chapter 6. Expressions which will r
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Chapter 6. Expressions Examples: As
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Chapter 6. Expressions • #active(
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Chapter 6. Expressions ✞ state si
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Chapter 6. Expressions Semantics: A
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Chapter 7 Patterns Syntax: pattern
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Chapter 7. Patterns In the followin
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Chapter 7. Patterns ✡✝ ✆ The
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Chapter 8 Bindings Syntax: bind = s
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Chapter 9 Value (Constant) Definiti
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Chapter 10 Instance Variables (VDM+
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Chapter 11 The State Definition (VD
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Chapter 11. The State Definition (V
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Chapter 12 Operation Definitions Op
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Chapter 12. Operation Definitions p
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Page 133 and 134: Chapter 14 Top-level Specification
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Page 173 and 174: Chapter 19 Static Semantics VDM spe
Page 175 and 176: Chapter 20 Scope Conflicts (VDM++ a
Page 177 and 178: References [Ada LRM] [Bicarregui&94
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Page 181 and 182: Appendix A The Syntax of the VDM La
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Appendix A. The Syntax of the VDM L
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Appendix B Lexical Specification B.
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Appendix B. Lexical Specification B
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Appendix B. Lexical Specification S
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Appendix C Operator Precedence The
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Appendix C. Operator Precedence eva
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Appendix C. Operator Precedence pre
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Appendix D Differences between the
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Index abs, 9 and, 6 card, 14 comp f
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INDEX arithmetic minus, 185 arithme
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INDEX boolean type, 6 char, 11 func
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INDEX sequence enumeration, 53, 187
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VDM-10 Language Manual

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