Flexible Embedded Control Systems : Design and Implementation

Embedded control system design is a complex and error prone task, and there is a great need for better development tools. Today most real-time control systems are static systems, designed in an ad-hoc fashion. A more interactive way of working would give shorter development times, reduced costs for testing, and safer, more robust systems. This thesis presents an interactive prototyping tool called Pålsjö and a controller description language called PAL. Pålsjö allows the user to interactively configure a system. Control systems are defined using block diagrams and blocks may be added and replaced on-line. The static nature of most embedded control systems makes them very sensitive to changes in the hardware or software configuration. There is rarely any interaction between the control loops and the underlying real-time kernel or operating system. From a control engineering perspective, the system executes in open loop. In this thesis, the possibility of using feedback in the scheduling of real-time tasks is explored. This is called feedback scheduling. An algorithm for selecting sampling rates based on the linear quadratic cost is presented. The dependence of the cost function on the sampling interval is investigated. The influence on the control performance from the interaction between the control tasks running concurrently in the real-time kernel is studied. A simulation toolbox for this is presented in the thesis. Designing flexible control systems is much simplified given the proper language support. Therefore the PAL language concept is extended into a new proposed language Friend, which is designed to support the development of flexible embedded control systems through the use of contracts