Design And Implementation Of Improved Ground Railway Signal Safety Computer Software

Rail signal is traditionally designed to follow the superposition principle to implement the entire system, different control functions use different subsystems, resulting complex structure, a number of devices, reliability and availability reducing, and hardware performance wasting. So it’s very necessary to find methods to reduce the number of rail signal equipments.In this paper, temporal and spatial isolation methods are used to integrate ground railway signal safety computer software. Isolating in time and space (memory) between subsystems to implement the functions of several devices in a single device. This integration method does not change the logical structure of train control systems, subsystems still logically independent, but only physically integrated into a single device.In time isolation, a two-level scheduling structure is used. In the lower layer time-slice isolating approach is used to make subsystems can not interfere with each other; in the upper layer real-time scheduling algorithm is used internal subsystems to improve system efficiency. RM algorithm is used in the upper layer because its theory is very mature and implementation is simple. In the lower layer, isolation parameters need to ensure that each subsystem allocated enough time to perform its functions, which requires calculation. In the first step running time of every task need to be measured. Choose path of software at first, and then calculate input of every path based on Relaxation Iteration Method, time functions provided by VxWorks are used to measure running time of every path, and choose the worst one as allocated time. In the second step, calculate isolation parameters according to the measurements.In memory isolation, a two-level scheduling structure is also used. In the lower layer MMU is used to set independent address space for each subsystem, making subsystems can only see its own address space thus they can not interfere with each other; in the upper layer improved dynamic memory allocation algorithms within subsystem is used to improve system efficiency and reduce fragmentation. System memory allocation strategy is modified to make different approach for big chunks and small ones. Original allocation and release method is still used for big chunks, while a method based on buffers is used for small chunks.Finally, based on a simplified CTCS-3train control system ground equipment features, a experimental verification is taken on simplified RBC, TSRS, TCC. Time and memory isolation are implemented using methods above. And a third party monitor is added to ensure subsystems normally switching. The integrated software successfully got the right outputs in every testing situation, proved the correctness and effectiveness of the whole approach of this article.