This chapter describes a concise case study of a real-time embedded system, namely a Pump Control System. Of particular interest are several periodic activities necessitating the design of periodic tasks, in addition to examples of task design with temporal and control clustering. There is also a need for a state machine that is designed with three separate orthogonal regions in order to separate three different but interrelated control concerns. This is one of the shorter case studies in which the details of dynamic interaction modeling (covered in detail in other case studies) are left as an exercise for the reader. The end product of dynamic interaction modeling is an integrated communication diagram, which is used to transition into design modeling.

The problem description is given in Section 22.1. Section 22.2 describes the structural modeling, and Section 22.3 describes the use case model. Section 22.4 describes the object and class structuring. Section 22.5 describes the state machine model. Section 22.6 describes the integrated interaction model, which is an outcome of dynamic interaction modeling. Section 22.7 describes the design modeling, which consists of the distributed software design and distributed software deployment. This is followed by the design of the concurrent task architecture and detailed software design.

PROBLEM DESCRIPTION

A Pump Control System for a mineral mine has several pumps situated underground, which are used to pump out water that has collected at the bottom of the mine. Each pump has an engine, which is controlled automatically by the system. The system uses Boolean high- and low-level water sensors, in addition to an analog methane sensor, to monitor the environment inside the mineral mine. Detection of the high water level causes the system to pump water out of the mine until the low water level is detected. For safety reasons, the system must switch off the pump when the level of methane in the atmosphere exceeds a preset safety limit. Once the pump has been switched off, five minutes must elapse before it can be switched on again. For each pump, status information on the methane and water level sensors, as well as the pump engine, is sent to a central server. Human operators can view the status of the various pumps.