Train Gate System

1
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.

2
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

3
Timing Requirements

• The arriving trains have an average inter-arrival
  period, avgP
• The gate takes z time units to close (or open).

4
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

5
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.

6
Timeouts

• Activity timeouts
• Communications timeout

7
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

8
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.

9
Sequence Diagram for Train Arrival
10
Main Class Diagram
11
Train Gate SystemCommunication Diagram
12
Entry Sensor
13
Revised Entry sensor
14
Exit Sensor
15
Revised Exit Sensor
16
Monitor
17
Revised Monitor
18
Controller Process
19
Revised Controller Process
20
Gate Process
21
Revised Gate