RealTime Bounded Buffer Problem

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Real-Time Bounded Buffer Problem

• The buffer is an intermediate storage of N slots.
  A data item can be stored in each slot
• The producer process inserts data items into the
  buffer, in the first available empty slot
• The consumer removes data items from the full
  slots

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Timed Producer Consumer
System Interconnection Diagram
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Channels in the Bounded Buffer

• There are three CRSM machines, one for the
  producer, one for the consumer, and one for the
  buffer
• There are two channels defined
• Deposit, from the producer to the buffer
• Remove, from the buffer to the consumer

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Communication Between The Producer and the Buffer

• In the producer, if the Deposit I/O does not
  occur on time, the producer changes to state P2,
  an error
• The Deposit I/O may occur if
• The producer is in state P1
• The Buffer is in state B1
• The guard, full lt n
• If this communication occurs, the two transitions
  occur simultaneously

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Communication Between The Producer and the Buffer
(2)

• If the communication from the producer to the
  buffer takes place, the buffer receives the data
  item in its next available slot
• Bufin data

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Communication Between The Buffer and the Consumer

• The Remove I/O may occur if
• The Consumer is in state C1
• The guard, full gt 0, is true
• The Buffer is in state B1

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Timed Bounded Buffer

• In the Buffer, the internal computation
  transitions has time constraint 2,3, which
  means the initial transition from state B0 to
  state B1 can take any time between 2 and 3 time
  units
• The Deposit and Remove transitions could occur at
  any time after entering state B1 provided the
  relevant guard evaluates to true.

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Time Constraints in Consumer and Producer

• The Consumer can execute a Remove sometime in the
  interval 8,10 after entering state C1.
• The Producer can perform a Deposit I/O only in
  the interval 7,12 after entering P1.

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Timeout in Producer-Consumer

• At relative time 12, a timeout occurs and the
  transition is taken to state P2, with the
  current time stored in variable now.
• A message is then sent on channel Error to an
  error-logging machine, and producer starts the
  cycle again.

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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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Physical Requirements

• The gate must be closed whenever there are trains
  in the area (safety requirement)
• The gate must be kept open when there are no
  trains in the area (liveness requirement)

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Timing Requirements

• The maximum allowed time (period) from the
  instance the train enters the approach zone and
  the instance the gate completes closing must be 8
  time units
• The maximum allowed period after a correct signal
  is received by the controller and the instance
  the corresponding command is sent to the gate is
  1.2 time units

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Timing Requirements

• The period from the instance the train leaves the
  gate to the instance the gate is raised should
  not be greater than 1.75 time units, if there are
  no more trains in the area.

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Timing Workload

• The arriving trains have an average inter-arrival
  period, tr_arr
• The gate takes z time units to close (or open)
• There is a communication delay in the
  communication of the controller and the gate.

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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

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Train Gate System CRSMCommunication Diagram
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Train-Gate SystemUML_RT Collaboration Diagram
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Timeouts

• Activity timeouts
• Communications timeout

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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

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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.

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Sequence Diagram for Train Arrival
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Main Class Diagram
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Entry Sensor
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Exit Sensor
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Monitor
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Controller Process
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Gate Process