Digital Sound Recorder: A case study on designing embedded systems using the UML notation.

Digital Sound Recorder: A case study on designing embedded systems using the UML notation.Ivan Porres PaltorÅbo Akademi University, Department of Computer Science, Lemminkäisenkatu 14, FIN-20520 Turku, Finland email: Ivan.Porres@abo.fiJohan LiliusÅbo Akademi University, Department of Computer Science, Lemminkäisenkatu 14, FIN-20520 Turku, Finland email: Johan.Lilius@abo.fiTurku Centre for Computer Science TUCS Technical Report No 234 January 1999 ISBN 952-12-0367-6 ISSN 1239-1891AbstractThis document is an example of the object-oriented analysis and design of an embedded system using the Unified Modelling Language (UML). The analysed system is a digital sound recorder, or Dictaphone. The design has been implemented using an embedded processor and the C++...
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Digital Sound Recorder: A case study on designing embedded systems using the UML notation. Digital Sound Recorder: A case study on designing embedded systems using the UML notation. Ivan Porres Paltor Åbo Akademi University, Department of Computer Science, Lemminkäisenkatu 14, FIN-20520 Turku, Finland email: Ivan.Porres@abo.fi Johan Lilius Åbo Akademi University, Department of Computer Science, Lemminkäisenkatu 14, FIN-20520 Turku, Finland email: Johan.Lilius@abo.fiTurku Centre for Computer ScienceTUCS Technical Report No 234January 1999ISBN 952-12-0367-6ISSN 1239-1891 AbstractThis document is an example of the object-oriented analysis and design ofan embedded system using the Unified Modelling Language (UML). Theanalysed system is a digital sound recorder, or Dictaphone. The design hasbeen implemented using an embedded processor and the C++ programminglanguage.Keywords: object-oriented design, UML, embedded systems. TUCS Research Group Programming Methodology Research Group1 IntroductionThe Unified Modelling Language [BJR1, BJR2], provides a standardised notation toexpress object-oriented software analysis and design [CY90, MO92, SS95]. UMLdiagrams are able to model complex software systems including real-time embeddedsystems.However, UML is not a software process. UML does not specify the different stages ofthe development of a software project. The UML standard specifies a notation forseveral different diagrams, but it does not describe how to create and apply eachdiagram. [Dou98] presents a methodology for building embedded systems using theUML notation and object-oriented analysis and design techniques.This document describes the object-oriented design and implementation of a digitalsound recorder, or Dictaphone, using the UML notation and the method described byDouglass.There are several digital sound recorders commercially available in the market. Themodel described here has been designed following the specifications of a commercialproduct from a well know manufacturer. These requirements are described in the secondsection of this document.The third section discusses the object model of the system and presents the main classdiagram. The fourth section continues the object-oriented analysis but focusing in thinternal behaviour of each object.The fifth section deals with the architectural design. We show the hardware architecturof the sound recorder and the concurrency model, where we assign each object to anexecution thread.The design continues defining the collaborations between the different objects. This isdone in section number six, where design patterns [GHJV95] are used to glue togetherthe classes defined in the analysis phase. The most specific design issues are discussedin the section number seven.Finally, The eighth section discusses the implementation. We have implemented thsoftware in the C++ programming language and built the hardware platform to run thecode using a 32 bits RISC embedded processor.1.2.2 Requirements AnalysisA digital sound recorder is a consumer electronic appliance designed to record and playback speech. The messages are recorded using a built-in microphone and they are storedin a digital memory. The user can quickly play back any message at any moment trougha speaker placed in the front of the device. It should be small, light, easy to use, andbattery operated.Figure 2.1 shows what our sound recorder could look like. It is a hand held unit withflat display and fairly large buttons. 1 Yes No Figure 2.1: External appearanceThe main features of the product that we are going to consider in our design are:• Capacity for ten different messages. The length of each message is limited by theavailable memory.• Easy to use with on screen menus.• Direct access to any message.• Alarm clock with year-2000-ready calendar. The user can set a daily alarm. The alarm beeps until the user presses a key, or after 60 seconds.• Full Function LCD Display. The current date and time is always shown in thedisplay. The display also shows clear directions about how to use it and what it is doing.• Battery-level indicator. The system beeps when the battery is low.• Stand-by mode. It economises the battery power. The system switches off thperipherals when they are not in use. The normal operation is resumed when the userpresses a key.• Good sound quality. Sound is processed at 6Khz using eight bits per sample.2.1 External EventsAn embedded system is constantly interacting with its environment. In this first stage ofthe analysis, we can consider our system as a black box reacting to the requests andmessages from the environment. The environment is composed of several agents. Eachagent interacts with our system with a different purpose and it exchanges a different setof messages.Context-Level DiagramFigure 2.2 shows all the agents that interact with our system. We have identified threagents: the user, the battery and the time. It also shows the interfaces, sensors andactuators that allow our system and the agents to exchange messages. These messagescan be requests from the agents to the system, or responses and services from thesystem to the agents. The sensors for the messages from the user are the microphoneand the buttons. The actuators for the user agent are the speaker and the display. Thebattery level meter senses the state of the battery. 2 Time next second Digital Sound Recorder Record Sensors/Actu ...