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Train Gate System. A one-directional railway track crosses a road A gate at the crossing may be lowered or raised under computer control A short distance from the crossing a sensor detects entering trains A short distance from the crossing a sensor detects leaving trains.
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Train Gate System • A one-directional railway track crosses a road • A gate at the crossing may be lowered or raised under computer control • A short distance from the crossing a sensor detects entering trains • A short distance from the crossing a sensor detects leaving trains.
Physical Requirements • The gate must be closed whenever there are trains in the area • The gate must be kept open when there are no trains in the area
Timing Requirements • The arriving trains have an average inter-arrival period, avgP • The gate takes z time units to close (or open).
Simulation Outputs • Trace of events • Performance measures • Number of trains serviced • Worst reaction time • Worst response time • Number of deadlines missed: • Gate opening/closing • Communication timeouts
Train Control • A physical safety requirement of the system is that the gate is closed whenever there are trains in the area • The physical liveness requirement is to keep the gate open if there are no trains in the area • The controller C controls the gate with the openg (og) and closeg (cg) commands.
Timeouts • Activity timeouts • Communications timeout
Activity Timeouts • The Gate takes a maximum of z time units to close or to open • The controller process normally waits for the Gate to open or close • If the Gate takes longer than the maximum allocated time, the controller flags a timeout for the gate and triggers an alarm
Communication Timeouts • The real-time systems uses synchronous communications • In the normal case, one of the processes, either the sender or the receiver, will wait for the other to establish the communication • A communication timer object will interrupt a process attempting to communicate, on timeout.
