This chapter describes a case study for a microwave oven control system. The software design for this embedded system is typical of many consumer products. Thus, the microwave oven embedded system interfaces with the external environment by means of several sensors and actuators, supports a simple user interface, keeps track of time, and provides centralized control that necessitates the design of a state machine. As the microwave oven is an embedded system, the design approach benefits from starting with a systems engineering perspective of the total hardware/software system before the software modeling and design.

The problem is described in Section 19.1. Section 19.2 describes structural modeling of the microwave oven embedded system, in which the system and software context block definition diagrams are developed. Section 19.3 describes the use case model for the microwave oven system. Section 19.4 describes how the object and class structuring criteria are applied to this system. Section 19.5 describes the design of the state machines for controlling the microwave oven. Section 19.6 describes how dynamic interaction modeling is used to develop sequence diagrams from the use cases. Section 19.7 describes the design modeling for the microwave oven software system, which is designed as a concurrent component-based software architecture based on architectural structure and communication patterns. Section 19.8 describes the performance analysis of the real-time design. Section 19.9 describes the design of components, interfaces, and connectors of the component-based software architecture. Section 19.10 describes detailed software design and Section 19.11 describes system deployment.

PROBLEM DESCRIPTION

The microwave oven has input buttons for selecting Cooking Time, Start, Minute Plus, Time of Day, and Cancel, as well as a numeric keypad. It also has a display to show the cooking time left and time of day. In addition, the oven has a microwave heating element for cooking the food, a door sensor to sense when the door is open, and a weight sensor to detect if there is an item in the oven. Cooking is only permitted when the door is closed and when there is something in the oven. The oven has several actuators. Besides the heating element, there are light, beeper, and turntable actuators.