1 / 29

Real-Time Systems

Real-Time Systems. time dependent control oriented driven by events rather than data. Control Flow Diagram. extension to data flow diagram to represent control flow rather than data flow

wirt
Download Presentation

Real-Time Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Real-Time Systems • time dependent • control oriented • driven by events rather than data

  2. Control Flow Diagram • extension to data flow diagram to represent control flow rather than data flow • contains same processes as the data flow diagram but instead of showing data flow, it diagrams control flow • diagram the events that cause the various process to be activated

  3. Control Flow Diagram (2) • together with the CSPEC (control specification) show • how software behaves when the event or control signal is sensed • which processes are invoked as a consequence of the occurrence of the event

  4. Control Flow Diagram (3) control item window into CSPEC

  5. Drawing a Control Flow Diagram • draw the data flow diagram and remove all of the data flow arrows • add control items and windows into CSPEC where needed

  6. A Data Flow Process Bubble current temperature status check temperature safe point temperature

  7. PSPEC for check temperature If current temperature> safe temperature then set status to “true”; else set status to “false”; end if;

  8. Control Flow Diagram for check temperature above safepoint check temperature

  9. Data Flow for Copier op commands and data copy status displays copy info produce user displays read op input manage copying reload reqs. problem indicator problem type reload status perform problem diagnosis reload paper

  10. Copier Events • start/stop • paper feed (jammed, empty, etc.) • finished

  11. Control Flow for Copier start/stop paper feed status alarm read op input manage copying produce user displays finished perform problem diagnosis reload paper full

  12. Determining Events • list all sensors that are read by software • list all interrupt conditions • list all switches activated by operator • list all data conditions • look at noun-verb combinations reviewing control items as possible CSPEC I/Os • identify states, how each state is reached, & define transitions between states

  13. Microwave Oven Events • Half Power -- user pressed • Full Power -- user pressed • Timer -- user set • Door open -- switch not closed • Door Closed -- switch is closed • Start -- user pressed • Timeout -- timer has finished

  14. Control Flow Diagram and CSPEC • event that flows from the outside world into | (CSPEC) implies the CSPEC will activate one or more processes in the CFD • A control item that emanates from a process and flows into | (CSPEC) implies control and activation of some other process or outside entity

  15. Events • events occur at discrete points in time and cause an instantaneous change in the state of a process • can occur asynchronously (any point in time) or synchronously (at clocked intervals)

  16. State Transition Diagrams • graphical representation of the events and the stimuli that cause transition from one event to another • above each transition list the input/output that cause/result from the stimuli and event.

  17. State Transition Diagrams possible state possible transition between states

  18. State Transition Matrix • uses a tabular rather than graphical form • all possible states identify the rows • all stimuli identify the columns • at intersection next possible state is listed • add column at end of matrix for outputs

  19. ON HOOK/QUIET BUSY DIAL BUSY NUMBER/ BUSY TONE DISTIN. DIAL TONE ON HOOK/QUIET DIAL 9/ DISTINCTIVE DIAL TONE DIAL IDLE NUMBER/ RING BACK TONE OFF HOOK/DIAL TONE CALLED PARTY OFF HOOK/ CONNECTED IDLE DIAL TONE DIAL IDLE NUMBER/ RING BACK TONE RINGING ON HOOK/QUIET DIAL BUSY NUMBER/ BUSY TONE BUSY ON HOOK/QUIET ON HOOK/QUIET

  20. The state diagram depends on the range of facilities on the CD player. Idle Door open Idle Off button Off button On button Ready Open door Door closed Off button Disk Door open Ready to play Door closed Off button Off button Door Close Play button End of play Track selector Disk playing Track selector Play button Track selection

  21. Microwave Oven Events • Half Power -- user pressed • Full Power -- user pressed • Timer -- user set • Door open -- switch not closed • Door Closed -- switch is closed • Start -- user pressed • Timeout -- timer has finished

  22. Full power on Full Power Timer Timer Full Power Idle Set time Timed operation Cooking complete Timeout Half Power Door closed Half Power Start Timer Half power on Door open Operation enabled Door open Idle Door closed Operation disabled

More Related