Software implementation techniques for HW/SW embedded systems

Our focus is the software implementation of control-oriented systems. Such a task is one of the least automated portions of the contemporary codesign process. In systems that must respond to external events, often several asynchronous tasks are implemented on the same processor. We are studying such systems because they often utilize a dynamic multi-rate scheduling technique using a multitasking real-time kernel. Based upon the MCSE functional model as a specification input, we propose a set of transformation rules that one can apply to the functional structure to reduce the complexity of the software design prior to implementation. We further show that after such optimizations, the microprocessor interrupt system can often be used as an efficient priority-based scheduler, thereby removing the need for a real-time kernel. The resulting implementation is described using a software implementation diagram from which it is easy to prove the timing constraints are satisfied. We use a simplified control system to illustrate our approach and to show a smooth incremental codesign path with a better integration of software estimates into the partitioning decision.