REAL-TIME SYSTEMS DESIGN AND ANALYSIS phần 6

được quy định sử dụng như là một bắt buộc cho hệ thống có kiến trúc đã được xác định chung được sử dụng để trích dẫn những điều mà các môi trường hoạt động hoặc phát triển để cung cấp khả năng được chỉ định Không nên dùng cho sử dụng | PROCEDURAL-ORIENTED DESIGN 241 Figure Context diagram evolution from context diagram to level 0 DFD to level 1 DFD and finally to a P-SPEC which is suitable for coding Laplante03b . DFD 0 Ax Ay Az 40b-ms Interrupt Temperature Other . 10-msi Physical Data Interrupt Diagnostics 40a-ms Interrupt Attitude Data 1000-ms Interrupt True Acceleration Velocity and Position Information Temperature Other Physical Data Diagnostics Information Torque Gyros Diagnostics Information Store and Transmit Data 3 Process Acceleromete Data Figure Level 0 DFD for the inertial measurement system. The dashed arcs represent control flow in the system. Attitude Data Display Information True Acceleration Velocity and Position Diagnostics Information Information _ Torquing Pulses gx gy gz 242 5 SOFTWARE SYSTEM DESIGN Validate Data Compute Pulses Output Pulses Check that data are within acceptable range If valid_data TRUE compute pulses as follows. Output torquing pulses as follows. Figure P-SPECs for DFD 1 Torque gyros. interface flow in the DFD. Data structure diagrams are also used to describe information about logical relationships in complex data structures. Data Dictionaries A data dictionary is a repository of data about data that describes every data entity in the system. This dictionary is an essential component of the structured design and includes entries for data flows control flows data stores data elements control elements. Each entry is identified by name range rate units and so forth. The dictionary is organized alphabetically for ease of use. Other than that there is no standard format but every design element should have an entry in it. Most CASE tools provide the data dictionary feature. For example each entry might be organized to contain the following information Entry type data flow data store terminator process Name PROCEDURAL-ORIENTED DESIGN 243 DFD 2 Process Accelerometer Data Temperature Other Physical Data True Acceleration .