Estimation of Worst-Case Execution Time WCET of code is of crucial importance since it can be used to determine the needed computation resources. This paper studies the WCET of PL programs which specify cyclic computing applications. The structure of a PL program di ers very much from that of a sequential program. A PL program contains declarative information of the data to be operated on and declarative information of the periodic processes. The WCET of a PL program is de ned as WCET for each

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... eriod of the cyclic application. The processes of a cyclic application may run in di erent execution modes depending on the context. Not every combination of modes is feasible. Two methods are provided to calculate the WCET of a PL program while taking the infeasibility constraints into account. One method uses Integer Linear Programming technique and the other uses heuristic search-based technique. Timing analysis for multiple-period PL programs is also studied in the paper. The calculated WCET can be used to validate the timing constraints of the system or to help to decide the sampling rates of the system.