SE 746-NT Embedded Software Systems Development Robert Oshana Lecture 14 For more information, plea

2. Real-Time Embedded Systems Design Process

3. Agenda Monitoring and control systems Control systems Data acquisition systems State machines

4. Monitoring and control systems Important class of real-time systems Continuously check sensors and take actions depending on sensor values Monitoring systems examine sensors and report their results Control systems take sensor values and control hardware actuators

5. Burglar alarm system A system is required to monitor sensors on doors and windows to detect the presence of intruders in a building When a sensor indicates a break-in, the system switches on lights around the area and calls police automatically The system should include provision for operation without a mains power supply

6. Burglar alarm system Sensors Movement detectors, window sensors, door sensors. 50 window sensors, 30 door sensors and 200 movement detectors Voltage drop sensor Actions When an intruder is detected, police are called automatically. Lights are switched on in rooms with active sensors. An audible alarm is switched on. The system switches automatically to backup power when a voltage drop is detected.

7. The R-T system design process 1. Identify stimuli and associated responses 2. Define the timing constraints associated with each stimulus and response 3. Allocate system functions to concurrent processes 4. Design algorithms for stimulus processing and response generation 5. Design a scheduling system which ensures that processes will always be scheduled to meet their deadlines

8. Stimuli to be processed Power failure Generated aperiodically by a circuit monitor. When received, the system must switch to backup power within 50 ms Intruder alarm Stimulus generated by system sensors. Response is to call the police, switch on building lights and the audible alarm

9. Timing requirements

10. Process architecture

11. Building_monitor proces1

12. Building_monitor process 2

13. Control systems A burglar alarm system is primarily a monitoring system It collects data from sensors but no real-time actuator control Control systems are similar but, in response to sensor values, the system sends control signals to actuators An example of a monitoring and control system is a system which monitors temperature and switches heaters on and off

14. A temperature control system

15. Data acquisition systems Collect data from sensors for subsequent processing and analysis Data collection processes and processing processes may have different periods and deadlines. Data collection may be faster than processing e.g. collecting information about an explosion Circular or ring buffers are a mechanism for smoothing speed differences

16. Reactor data collection A system collects data from a set of sensors monitoring the neutron flux from a nuclear reactor Flux data is placed in a ring buffer for later processing The ring buffer is itself implemented as a concurrent process so that the collection and processing processes may be synchronized

17. Reactor flux monitoring

18. A ring buffer

19. Mutual exclusion Producer processes collect data and add it to the buffer Consumer processes take data from the buffer and make elements available Producer and consumer processes must be mutually excluded from accessing the same element The buffer must stop producer processes adding information to a full buffer and consumer processes trying to take information from an empty buffer

20. Java implementation of a ring buffer 1

21. Java implementation of a ring buffer 2

24. Finite state machines

25. Finite State Machines(FSMs) Widely used specification technique Used to specify system behavior in response to events Both output and next state can be determined solely on the basis of understanding the current state and the event that caused the transition H/W engineers have been using FSM for years

31. State Machines Models how a system responds differently to events over time

33. States

35. Finite State Machines State the memory of previous events Events inputs to a system Actions output in some form mechanical, electrical or software event

36. Finite State Machines State the memory of previous events Events inputs to a system Actions output in some form mechanical, electrical or software event

37. Coke Machine Events coin insertion Actions coke delivery coins returned State the memory of how much money has been deposited

38. FSM Diagram

39. FSM

40. ScenarioQuarters Only, 75 cents Customer enter quarter Customer enter quarter Customer enter quarter Coke Machine deliver coke

41. Enumerate Events & Actions

43. State Transition Table

48. Transition Table State E1 E2 A B B C A/coin return C A/coke A/coin return

51. Telephone System FSMLocal 4-digit exchange

55. From the article “Embedded State Machine Implementation” Martin Gomez Embedded systems programming

56. Embedded state machines Many embedded software applications are natural candidates for mechanization as a state machine Program that must sequence a series of actions, or handle inputs differently depending on what mode its in Soft key interfaces to comm protocols

57. State machines An algorithm that can be in one of a small number of states Mealey Output a function of present state and output Moore Function only of state

58. Example state machine

59. State machine approach Learn what the user wants Sketch the state transition diagram Code the skeleton of the state machine, without filling in the details of the transition actions Make sure the transitions work properly Flesh out the transition details Test

60. Another example Program that controls the retraction and extension of an airplane’s landing gear Hardware Nose gear Left main gear Right main gear Hydraulically actuated

61. What does the user want? “don’t retract the landing gear if the airplane is on the ground” Is it ok to retract the landing gear the instant the airplane leaves the ground? Use a white board or sequence enumeration! <event that caused transition>/<output as a result of the transition>

62. First implementation – only does what the user asked for

63. Some things to keep in mind Computers are very fast compared to mechanical hardware – you may have to wait Mechanical engineer may not know as much about computers! What happens if parts break?

64. A better implementation

65. Implementation

69. RaisingGear() function

70. Testing Test plan almost writes itself Avoid hidden states Number of transitions is measure of systems complexity Use print statement to output current state Be careful when connecting to actual hardware