The calculation results of the embedded real-time system correctness depends not only on the logical system, and the results also spent time, the system must ensure in response to external events in a predictable period of time. Worst Execution Time (the worst case execution time (Case) is the maximum execution time of the program in the process of running. It plays a very important role in the research of real time scheduling, task priority arbitration, resource conflict arbitration; inter task communication and hardware / software partitioning. This paper focuses on the specific hardware platform (ARM7TDMI processor), the worst case Garfield system MP3 decoding program execution time (WCET) were evaluated on the MP3 decoding program optimization and give objective evaluation, but also provide important basis for the division of hardware and software of MP3 module. The worst case execution time (WCET) calculation is mainly related to two aspects: the high level analysis (Analysis High-Level) and the underlying modeling (Modeling Low-Level). High level analysis is to analyze the program structure in a high level language, find out the sequence of instructions in the worst case, while the bottom is built hardware model in assembly environment, the worst case has a known sequence of instructions execution time. The complexity of the WCET calculation limits the size of the analyzed program and the accuracy of the calculation. This paper introduces an effective method to calculate the worst-case execution time (WCET), and develops a path analysis tool CRYINGCAT. The path analysis tools to get the instruction execution time from the bottom of the model, the anti mark flow graph analysis control extracted from the top (Control Flow Graph), and then use the containing control execution time information flow diagram to establish the integer linear programming model, and finally through the worst case solving integer linear programming model to obtain the execution time of the program (WCET). Prior informed system program in the worst case execution time (Worst-Case Execution, Time, WCET) is the design and verification of real-time scheduling and schedulability analysis of the premise, but also to determine whether the periodic tasks meet their performance goals, in order to find the basis system performance bottleneck. This paper summarizes the analysis methods of WCET program, describes the definition and composition of WCET analysis, summarize the program flow fact analysis method, and points out the research program flow fact analysis and WCET analysis of the existing problems.
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