In this paper we are primarily concerned with embedded real-time systems such as mobile phones or personal communication devices. Today personal communication devices are more than voice call terminals. Mobile phones serve as platforms for a variety of mobile applications including text and picture messaging as well as personal information management, including data synchronization with remote servers and desktop computers. Mobile phones host a range of communication-centered applications most of which have real-time constraints. During a voice call speech data must be processed in a timely fashion to avoid jitter. During a GPRS session lower layer packets arrive every 10 ms. These are just few examples of system requirements that lead to tight software performance constraints.