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.

Sequence Diagram for Train Arrival

Main Class Diagram

Train Gate SystemCommunication Diagram

Entry Sensor

Revised Entry sensor

Exit Sensor

Revised Exit Sensor

Monitor

Revised Monitor

Controller Process

Revised Controller Process

Gate Process

Revised Gate