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Embedded Systems September 2000 Vol13_10

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The hard pa rt is being a ble to FIGURE 3 Quarter Soda deposited -~~ Soda select ----- Change return Sold out light Sold out Power on light Initialize Change returned de termine all the possible types of inte raction with the system. One com- mon technique for describing the sys- tem behavior is use cases. Use cases are textual narra tive descriptions of the processes in an ente rprise or sys- tem. They are used to explo re and elicit requirements and can help determine which types of in teraction to expect between the actors (external stimuli to the system) and the system. But use cases may not always combine to describe comple te and consistent behavior. Use cases can be used to explore the problem domain and to perform fro n t-end d oma in a nalys is. Othe r techniques can then be used to fully specify the solutio n stra tegy. One technique that has worked well in our embedded system proj ect is called sequence enumeration. You always believed there were more lntetugent embedded tools out there. People doubted th ei r existence - yet you continued to search- and now you've found them. COSMIC C compilers are fast, effi cient, reliable, and produce the tightest object code available. Cosmic Software's embedded development tools offer portability fo r a complete line of micro- controllers. All toolkits include IDEA, our intuitive IDE that provides everything you need in a single, seamless Windows framework. You were right. Gw..!.li E-mail: c-tools@cosmic-us.com www.cosmic-software.com Phone: US ... 781 932-2556 France ..... 33 1 4399 5390 UK ........ 44 01256 843400 Germany ... 49 0711 4204062 Sweden .... 46 31704 3920 Add ZAP, our non-intrusive source- level debuggers and minimize your test cycle too. Want proof of their existence? Download a free evalu ation copy of our development tools at www.cosmic-software.com or call Cosmic today. Cosmic supports the Motorola family of microcontrollers: 68HC05, 68HC08, 68HC11. 68HC12, 68HC16, 68300 and STMicroelectronics' ST7 Family. 118 SEPTEMBER 2000 Embedded Syst ems Programming Sequence enumeration Seque nce enumeratio n is a theoreti- cally sound and hig hly practical approach to describing the external (or black box) behavior of a system. Sequence enume ra tion is a way of specifyi ng and mapping stimuli and responses of an embedded system. This approach conside rs all permuta- tions of input stimuli. Sequence enu- me rations consist of a list of pr ior stimuli and current stimuli as well as a respo nse fo r that particular stimuli given the prior history. Equivalent his- tories are used to map certain responses. This technique maps directly to a sta te machine impleme n- tation. The strength of sequence enu- me ra tions is tha t the technique requires the develope r to consider the obscure sequences that a re usually overlooked. As an example, I will consider the simple soda machine shown in Figure 1. A set of natural language require- ments fo r this system is shown in Figure 2. To sta rt with, a use case can be developed that describes one type of in teraction with the system. A use case

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