Next State:UML Statecharts

Action: prepare RTOS, fine-tune for acceptable real-time performance, plan for difficult validation and verification, be prepared to explain non-deterministic behavior and other anomalies, update resume, check out Staccato™

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Next State: Staccato™

Action: be prepared for excellent real-time performance and fully-deterministic behavior, welcome validation and verification, add IEEE-CEUs to your resume, modestly accept your bonus, raise and promotion. Click here to get started...

Classical Mealy/Moore Finite State Machines have been used in the design of embedded software applications likely since the 1970's, using either assembly or the C-language. Using Finite State Machines in embedded software has never achieved the status of a 'de-facto standard', and to this day, FSMs are likely used in only a small percentage of deployed embedded systems. This may seem surprising, since 'embedded systems' implies strong coupling between hardware and software, and the fact that Finite State Machines have been the heart of digital sequential circuit design (i.e. microprocessors, microcontrollers, communication controllers, etc) even prior to that time. As hardware engineers originally took on the task of writing software/firmware, it was soon recognized that software development should be performed by more creative types, resulting in not only a separation of activities, but also of mindsets and territorial claims and responsibilities. Much 'finger-pointing' occurred between hardware and software groups when things went wrong, which likely set the foundation for software types to seek new solutions and methods among their own, as computer scientists and engineers. This separation of hardware and software was inevitable and necessary to the evolution of the entire embedded industry, but unfortunately it seems, the usefulness of Finite State Machine concepts in software got lost in the rubble, save a few who, to this day, will attest to FSMs as being most beneficial even to software development.

Eventually, the C-language evolved into C++ to address more esoteric challenges, and in the 1990's, embedded software engineers were found scratching their heads trying to adopt the concepts of polymorphism, abstraction and inheritance to make their products safer, more reliable and less costly to develop. A decade later, the Unified Modeling Language (UML) was developed to provide more structure and modeling capabilities to the realm of software development for enterprise/desktop applications. To achieve broader acceptance among the embedded community of developers, or possibly recognizing the usefulness of Finite State Machine concepts, the UML 2.0 specification added Statecharts, based on Harel[87]. Statecharts claims advancements over the classical Mealy/Moore paradigm by adding two new concepts: hierarchical (nested) state machines and orthogonality (independence and concurrency).

Even though the UML is a 'modeling language' and Statecharts a 'Visual Formalism for Complex Reactive Systems', many products based on UML and Statecharts offer visual FSM development tools and auto-code generation capabilities. The execution framework for the resulting FSM code is usually a Real-Time Operating System, or RTOS, which, for the most part, is a derivation of enterprise/desktop computer operating systems, customized to meet the real-time requirements of most embedded systems. These (real-time) operating systems are complex and quite non-deterministic, characteristics which must be addressed for any embedded system, using FSMs or not.

So, on one hand, if an embedded systems software developer decides to use Finite State Machine concepts on a project, he/she will need to have a comprehensive understanding of the Object-Oriented concepts of polymorphism, inheritance and abstraction, the UML Statechart concepts of hierarchical Finite State Machines and orthogonality, and real-time operating system (RTOSes) kernals and schedulers, plus some basic Mealy and Moore concepts. Now let's add up the cost of development tools, training and learning curves, licenses, etc...

On the other hand, embedded software developers can choose Staccato™ as an embedded system software architecture using Finite State Machines. No RTOS is needed, as Staccato™ FSMs are executed directly and continuously by an executive, providing exceptional real-time performance. Statechart orthognonality (or concurrency/AND states) is inherent in the Staccato™ method of partitioning a system by resource, resulting in a 'system of Finite State Machine-encoded tasks'. Staccato™ is based on classic Mealy and Moore state machines without the need for, or perceived benefits of, polymorphism, inheritance or abstraction as provided by the C++ programming language. The Staccato™ Crossroads SDK provides IEEE-CEU Certified Training; all that is needed to implement Staccato™ in your embedded system software is an ANSI-Compliant C Compiler as part of your software development toolchain.

Staccato™ uses a simplified state table concept to provide direct and continuous execution of FSM-encoded tasks. These basic concepts are discussed in much detail with many examples in the Staccato™ Crossroads SDK, taking the confusion and unnecessary complexity out of the process of using Finite State Machines for your embedded system software architecture.

For more information on UML and Statechart-based products, check out these links: