The Design And Implement Of QNX-Based Real-time Muti-channel Digital Synchronized Log (Record Unit)

The Multi-channel Digital Synchronized Log (MDSL) is a hi-tech product developed by Institute of Image & Graphics, Sichuan University, which is used mainly for recording synchronously the radar data and the dialogue between pilots and the control tower for airdrome and airline companies. The voice and radar data in MDSL is an important testimony in the analysis of aero accident, so the reliability of recording and the synchronization of voice data and radar data reordered are the first requirement for the MDSL system. The system is a typical real time system. In the former version of MDSL system, the record-unit is based on DOS that is not real time OS, so to enhance the reliability of system in all rates of input data flow we redeveloped the system based on the QNX, which is an excellent real time OS.Analyzing the system's requirement is one of the important part of my task, which is also key to design and coding. A good analyzing can reduce the bug of the design and reduce the cost of code-correcting for ambiguous requirement. I finished the analyzing of the requirement of the MDSL system by the SART (Structured Analysis for Real Time) successfully, that ensured the design and coding effective.Additionally, the design and coding of the record-unit subsystem are also my primary tasks. I designed and implemented the record-unit subsystem with mutil-thread by the method of Structured Design. The most difficult task of the design is to arrange the privilege of all task to ensure the system's response to external real-time event timely, to avoid the deadlock, to decrease the priority inversion and to enhance the ability of fault-tolerance.This Paper introduced briefly the requirement of the MDSL system analyzed by SART and the design of the record-unit subsystem. At the end of the paper, we analyze the real time schedulability of the recorder-unit subsystem by the RMA (Rate-Monotonic Analysis). We proved that the system is schedulable and the time requirement can be met by the RMA analysis and the practical testing.