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CSCE 3612 ch6-1 - Processes and operating systems Multiple...

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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Processes and operating systems Multiple tasks and multiple processes. Specifications of process timing. Preemptive real-time operating systems. Processes and UML.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Reactive systems Respond to external events. Engine controller. Seat belt monitor. Requires real-time response. System architecture. Program implementation. May require a chain reaction among  multiple processors.
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Tasks and processes A task is a functional  description of a  connected set of  operations. (Task can also mean  a collection of  processes.) A process is a  unique  execution  of a program. Several copies of a  program may run  simultaneously or at  different times. A process has its own  state: registers; memory. The operating system  manages processes. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Why multiple processes? Multiple tasks means multiple processes. Processes help with timing complexity: multiple rates multimedia automotive asynchronous input user interfaces communication systems
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Multi-rate systems Tasks may be synchronous or  asynchronous. Synchronous tasks may recur at different  rates. Processes run at different rates based on  computational needs of the tasks.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Example: engine control Tasks: spark control crankshaft sensing fuel/air mixture oxygen sensor Kalman filter engine controller
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Typical rates in engine controllers Variable Full range time (ms) Update period (ms) Engine spark timing 300 2 Throttle 40 2 Air flow 30 4 Battery voltage 80 4 Fuel flow 250 10 Recycled exhaust gas 500 25 Status switches 100 20 Air temperature Seconds 400 Barometric pressure Seconds 1000 Spark (dwell) 10 1 Fuel adjustment 80 8 Carburetor 500 25 Mode actuators 100 100 © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Real-time systems Perform a computation to conform to external  timing constraints. Deadline frequency: Periodic . Aperiodic . Deadline type: Hard : failure to meet deadline causes system failure. Soft : failure to meet deadline causes degraded  response.
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