Practical UML Statecharts in C/C++

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1 Practical UML Statecharts in C/C++ Event-Driven Programming for Embedded Systems 2nd Edition Miro Samek ELSEVIER AMSTERDAM. BOSTON. HEIDELBERG LONDON NEW YORK. OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Newnes is an imprint of Elsevier

2 Part I: Uml State Machines 1 Chapter 1: Getting Started with UML State Machines and Event-Driven Programming Installing the Accompanying Code Let's Play Running the DOS Version Running the Stellaris Version The main() Function The Design of the "Fly 'n' Shoot" Game Active Objects in the "Fly 'n' Shoot" Game The Missile Active Object The Ship Active Object..' The Tunnel Active Object The Mine Components Events in the "Fly 'n' Shoot" Game Generating, Posting, and Publishing Events Coding Hierarchical State Machines Step 1: Defining the Ship Structure Step 2: Initializing the State Machine Step 3: Defining State-Handler Functions The Execution Model Simple Nonpreemptive "Vanilla" Scheduler The QK Preemptive Kernel Traditional OS/RTOS Comparison to the Traditional Approach Summary 52 Chapter 2: A Crash Course in UML State Machines The Oversimplification of the Event-Action Paradigm Basic State Machine Concepts States State Diagrams 61

3 vi Table of Contents State Diagrams versus Flowcharts Extended State Machines Guard Conditions Events Actions and Transitions Run-to-Completion Execution Model UML Extensions to the Traditional FSM Formalism Reuse of Behavior in Reactive Systems Hierarchically Nested States Behavioral Inheritance Liskov Substitution Principle for States Orthogonal Regions Entry and Exit Actions Internal Transitions Transition Execution Sequence Local versus External Transitions Event Types in the UML Event Deferral Pseudostates UML Statecharts and Automatic Code Synthesis The Limitations of the UML State Diagrams UML State Machine Semantics: An Exhaustive Example Designing A UML State Machine Problem Specification High-Level Design Scavenging for Reuse Elaborating Composite States Refining the Behavior Final Touches Summary 96 Chapter 3: Standard State Machine Implementations The Time-Bomb Example Executing the Example Code A Generic State Machine Interface Representing Events Nested Switch Statement Example Implementation Consequences Variations of the Technique State Table Generic State-Table Event Processor Application-Specific Code 118

4 vii Consequences Variations of the Technique Object-Oriented State Design Pattern Example Implementation Consequences Variations of the Technique QEP FSM Implementation Generic QEP Event Processor Application-Specific Code Consequences Variations of the Technique General Discussion of State Machine Implementations Role of Pointers to Functions State Machines and C++ Exception Handling Implementing Guards and Choice Pseudostates Implementing Entry and Exit Actions Summary 146 Chapter 4: Hierarchical Event Processor Implementation Key Features of the QEP Event Processor :' QEP Structure QEP Source Code Organization Events Event Signal (QSignal) QEvent Structure in C QEvent Structure in C Hierarchical State-Handler Functions Designating the Superstate (Q_SUPER() Macro) Hierarchical State-Handler Function Example in C Hierarchical State-Handler Function Example in C Hierarchical State Machine Class Hierarchical State Machine in C (Structure QHsm) Hierarchical State Machine in C++ (Class QHsm) The Top State and the Initial Pseudostate Entry/Exit Actions and Nested Initial Transitions Reserved Events and Helper Macros in QEP Topmost Initial Transition (QHsm_init ()) Dispatching Events (QHsm_dispatch (), General Structure) Executing a Transition in the State Machine (QHsm_dispatch (), Transition) Summary of Steps for Implementing HSMs with QEP Step 1: Enumerating Signals Step 2: Defining Events 185

5 viii Table of Contents Step 3: Deriving the Specific State Machine Step 4: Defining the Initial Pseudostate Step 5: Defining the State-Handler Functions Coding Entry and Exit Actions Coding Initial Transitions Coding Internal Transitions Coding Regular Transitions Coding Guard Conditions Pitfalls to Avoid While Coding State Machines with QEP Incomplete State Handlers Ill-Formed State Handlers State Transition Inside Entry or Exit Action Incorrect Casting of Event Pointers Accessing Event Parameters in Entry/Exit Actions or Initial Transitions Targeting a Nonsubstate in the Initial Transition Code Outside the switch Statement Suboptimal Signal Granularity Violating the Run-to-Completion Semantics Inadvertent Corruption of the Current Event Porting and Configuring QEP Summary 201 Chapter 5: State Patterns Ultimate Hook Intent Problem Solution Sample Code Consequences Reminder Intent Problem Solution Sample Code Consequences Deferred Event Intent Problem Solution Sample Code Consequences Known Uses 230

6 ix 5.4 Orthogonal Component Intent Problem Solution Sample Code Consequences Known Uses Transition to History Intent Problem Solution Sample Code Consequences Known Uses Summary 251 Part II: Real-Time Framework, 253 Chapter 6: Real-Time Framework Concepts.' Inversion of Control CPU Management Traditional Sequential Systems Traditional Multitasking Systems Traditional Event-Driven Systems Active Object Computing Model System Structure Asynchronous Communication Run-to-Completion Encapsulation Support for State Machines Traditional Preemptive Kernel/RTOS Cooperative Vanilla Kernel Preemptive RTC Kernel Event Delivery Mechanisms Direct Event Posting Publish-Subscribe Event Memory Management Copying Entire Events Zero-Copy Event Delivery Static and Dynamic Events Multicasting Events and the Reference-Counting Algorithm Automatic Garbage Collection Event Ownership 288 i J 1 ' if " 'O "r j cori L 'S^JI

7 6.5.7 Memory Pools Time Management Time Events System Clock Tick Error and Exception Handling Design by Contract Errors versus Exceptional Conditions Customizable Assertions in C and C State-Based Handling of Exceptional Conditions Shipping with Assertions Asserting Guaranteed Event Delivery Framework-Based Software Tracing Summary 304 Chapter 7: Real-Time Framework Implementation Key Features of the QF Real-Time Framework Source Code Portability Scalability ' Support for Modern State Machines Direct Event Posting and Publish-Subscribe Event Delivery Zero-Copy Event Memory Management Open-Ended Number of Time Events Native Event Queues Native Memory Pool Built-in "Vanilla" Scheduler Tight Integration with the QK Preemptive Kernel Low-Power Architecture Assertion-Based Error Handling Built-in Software Tracing Instrumentation QF Structure QF Source Code Organization Critical Sections in QF Saving and Restoring the Interrupt Status Unconditional Locking and Unlocking Interrupts Internal QF Macros for Interrupt Locking/Unlocking Active Objects Internal State Machine of an Active Object Event Queue of an Active Object Thread of Execution and Active Object Priority Event Management in QF Event Structure Dynamic Event Allocation 335

8 xi Automatic Garbage Collection Deferring and Recalling Events Event Delivery Mechanisms in QF Direct Event Posting Publish-Subscribe Event Delivery Time Management Time Event Structure and Interface The System Clock Tick and the QF_tick () Function Arming and Disarming a Time Event Native QF Event Queue The QEQueue Structure Initialization of QEQueue The Native QF Active Object Queue The "Raw" Thread-Safe Queue Native QF Memory Pool Initialization of the Native QF Memory Pool Obtaining a Memory Block from the Pool Recycling a Memory Block Back to the Pool Native QF Priority Set Native Cooperative "Vanilla" Kernel The qvanilla.c Source File The qvanilla.h Header File QP Reference Manual Summary 387 Chapter 8: Porting and Configuring QF The QP Platform Abstraction Layer Building QP Applications Building QP Libraries Directories and Files The qep_port.h Header File The qf_port.h Header File 400 Types of Platform-Specific QActive Data Members 402 Base Class for Derivation of QActive 402 The Maximum Number of Active Objects in the Application 403 Various Object Sizes Within the QF Framework 403 QF Critical Section Mechanism 404 Include Files Used by this QF Port 404 Interface Used Only Inside QF, But Not in Applications 405 Active Object Event Queue Operations 406 QF Event Pool Operations The qf_port.c Source File The qp_port.h Header File 411 I

9 xii Table of Contents Platform-Specific QF Callback Functions System Clock Tick (Calling QF_tick()) Building the QF Library Porting the Cooperative "Vanilla" Kernel The qep_port.h Header File The qf_port.h Header File The System Clock Tick (QF_tick()) Idle Processing (QF_onidle ()) QF Port to uc/os-ii (Conventional RTOS) The qep_port.h Header File The qf_port.h Header File The qf_port. c Source File Building the uc/os-ii Port The System Clock Tick (QF_tick ()) Idle Processing QF Port to Linux (Conventional POSIX-Compliant OS) The qep_port.h Header File The qf_port.h Header File The qf_port. c Source File Summary 441 Chapter 9: Developing QP Application Guidelines for Developing QP Applications Rules Heuristics The Dining Philosopher Problem Step 1: Requirements Step 2: Sequence Diagrams Step 3: Signals, Events, and Active Objects Step 4: State Machines Step 5: Initializing and Starting the Application Step 6: Gracefully Terminating the Application Running DPP on Various Platforms "Vanilla" Kernel on DOS "Vanilla" Kernel on Cortex-M uc/os-ii Linux Sizing Event Queues and Event Pools In Sizing Event Queues Sizing Event Pools System Integration Summary 480

10 xiii Chapter 10: Preemptive Run-to-Completion Kernel Reasons for Choosing a Preemptive Kernel Introduction to RTC Kernels Preemptive Multitasking with a Single Stack Nonblocking Kernel Synchronous and Asynchronous Preemptions Stack Utilization Comparison to Traditional Preemptive Kernels QK Implementation QK Source Code Organization The qk.h Header File Interrupt Processing The qk_sched.c Source File (QK Scheduler) The qk.c Source File (QK Startup and Idle Loop) Advanced QK Features Priority-Ceiling Mutex Thread-Local Storage Extended Context Switch (Coprocessor Support) Porting QK The qep_port.h Header File The qf_port.h Header File The qk_port.h Header File Saving and Restoring FPU Context Testing the QK Port Asynchronous Preemption Demonstration Priority-Ceiling Mutex Demonstration TLS Demonstration Extended Context Switch Demonstration Summary 540 Chapter 11: Software Tracing for Event-Driven Systems Software Tracing Concepts Quantum Spy Software-Tracing System Example of a Software-Tracing Session The Human-Readable Trace Output QS Target Component QS Source Code Organization The QS Platform-Independent Header Files qs. h and qs_dummy. h QS Critical Section General Structure of QS Records QS Filters 562 Global On/Off Filter 562

11 xiv Table of Contents Local Filters QS Data Protocol 566 Transparency 567 Endianness QS Trace Buffer 569 Initializing the QS Trace Buffer QS_initBuf () 569 Byte-Oriented Interface: QS_getByte() 571 Block-Oriented Interface: QS_getBlock() Dictionary Trace Records 574 Object Dictionaries 575 Function Dictionaries 577 Signal Dictionaries Application-Specific QS Trace Records Porting and Configuring QS The QSPY Host Application Installing QSPY Building QSPY Application from Sources 584 Building QSPY for Windows with Visual C Building QSPY for Windows with MinGW 584 Building QSPY for Linux Invoking QSPY Exporting Trace Data to MATLAB Analyzing Trace Data with MATLAB MATLAB Output File MATLAB Script qspy.m MATLAB Matrices Generated by qspy.m Adding QS Software Tracing to a QP Application Initializing QS and Setting Up the Filters Defining Platform-Specific QS Callbacks Generating QS Timestamps with the QS_onGetTime () Callback Generating QS Dictionary Records from Active Objects Adding Application-Specific Trace Records "QSPY Reference Manual" Summary 608 Chapter 12: QP-nano: How Small Can You Co? Key Features of QP-nano Implementing the "Fly 'n' Shoot" example with QP-nano The main () function The qpn_port.h Header File 618 o@ 000

12 xv Signals, Events, and Active Objects in the "Fly 'n' Shoot" Game Implementing the Ship Active Object in QP-nano Time Events in QP-nano Board Support Package for "Fly 'n' Shoot" Application in QP-nano Building the "Fly 'n' Shoot" QP-nano Application QP-nano Structure QP-nano Source Code, Examples, and Documentation Critical Sections in QP-nano 634 Task-Level Interrupt Locking 635 ISR-Level Interrupt Locking State Machines in QP-nano Active Objects in QP-nano The System Clock Tick in QP-nano Event Queues in QP-nano The Ready-Set in QP-nano (QF_readySet_) Posting Events from the Task Level (QActive_post ()) Posting Events from the ISR Level (QActive_postlSR()) The Cooperative "Vanilla" Kernel in QP-nano Interrupt Processing Under the "Vanilla" Kernel Idle Processing under the "Vanilla" Kernel The Preemptive Run-to-Completion QK-nano Kernel QK-nano Interface qkn.h Starting Active Objects and the QK-nano Idle Loop The QK-nano Scheduler Interrupt Processing in QK-nano Priority Ceiling Mutex in QK-nano The PELICAN Crossing Example PELICAN Crossing State Machine The Pedestrian Active Object QP-nano Port to MSP430 with QK-nano Kernel QP-nano Memory Usage Summary 678 Appendix A. Licensing Policy for QP and QP-nano 679 A.I Open-Source Licensing 679 A.2 Closed-Source Licensing 680 A.3 Evaluating the Software 680 A.4 NonProfits, Academic Institutions, and Private Individuals 680 A.5 GNU General Public License Version 2 681

13 XVI Table of Contents Appendix B. Guide to Notation 685 B.I Class Diagrams 685 B.2 State Diagrams 688 B.3 Sequence Diagrams 689 B.4 Timing Diagrams 690 Bibliography 693 Index 699 o<s 0DC

Updates and Errata. Document Revision C for QP version February 2012

Updates and Errata. Document Revision C for QP version February 2012 Updates and Errata Document Revision C for QP version 4.4.00 February 2012 Index of Corrections and Updates NOTE: The following index uses the section numbering consistent with the book. Practical UML