Specification and Verification of Task-Level Time Constraints in Event-B

R177-time systems rely on components that have time constraints to be met. Specification and verification of time constraints is a critical issue of developing such systems. Event-B is a formalism for system modeling and analysis with advantages of mechanized proof and refinement scheme. But it does not directly support the modeling of timing properties. There have been some researches that introduce time concepts to the Event-B language or construct patterns facilitating the specification of timing properties. However, these are mainly concerned with the logical relations between events without the consideration of task-level time constraints. In this paper we identify some task-level time constraints, i.e., coincidence, exclusion and precedence, in real-time systems. For each constraint, we build its pattern from abstract to concrete. Such patterns can be integrated with existing Event-B models smoothly without the adjustment of the Event-B language. Our patterns can potentially be applicable to a wide range of modeling safety critical real-time systems. Furthermore, our work provides a reference for the formal specification of some other task-level time constraints.