Examples of embedded and real-time systems

1. Examples of embedded and real-time systems • Digital watch - Video game • Space craft - Airbag system • Digital still camera - Cell phone An embedded system is a computer whose end function is not to be a computer. For example, a microwave oven contains a computer, but obviously it's end function is to heat up food. A television contains a computer, but it's end function is to display audio and video. A Real-Time System responds in a (timely) predictable way to unpredictable external stimuli arrivals. In short, a Real-Time System has to fulfill under extreme load conditions: • timeliness: meet deadlines, it is required that the application has to finish certain tasks within the time boundaries it has to respect. • simultaneity or simultaneous processing: more than one event may happen simultaneously, all deadlines should be met. • predictability: the real-time system has to react to all possible events in a predictable way. • dependability or trustworthiness: it is necessary that the real-time system environment can rely on it

2. Embedded system components Software Memory FPGA/ ASIC A/D conversion CPU D/A conversion Actuators Sensors User interface Aux system (power cooling, etc Diagnostic port Electromechanical Backup and safety External environment

3. Embedded systems- Example Digital watch • Requirements • Presentation of date and time with accuracy to the nearest second • Measurement of the length of an event to the nearest 100th of a second • Audible sound at certain time periods • Not much processing power is required to do this

4. Digital watch • Typical digital watch is an 8-bit processor • Usually has its own on-chip ROM • May not require any RAM at all if sufficient registers are on-chip • Processor, memory, counters, real-time clock all on one chip

5. Digital watch • Other hardware • Inputs (buttons on the watch) • Outputs (LCD and speaker) • Designer’s goals: • Reasonably reliable product • Extraordinarily low production cost • Support product line architecture • Low cost versions can eliminate stopwatch buttons or the speaker • Would limit functionality but may not change software at all • Development cost can be higher • Amortized over thousands or millions of units

6. Video game player • Nintendo games and Play station games are examples of embedded systems • Very powerful machines • Relatively inexpensive compared to PCs • Big challenges - high processing power and low production cost

7. Video game player • Develop cost is usually not an issue • Custom processors if necessary • Special demands of video games • Production cost must be low (approx $100) • Shift costs if possible • Move memory and other peripherals from the main circuit board to the game cartridges • Decreases cost of unit and increases cost of each game

8. Video game player • 64-bit processor ends up having only a few MB of memory • Enough to boot the system to a state where it can access memory on the game cartridge

9. Mars Explorer • Unmanned spacecraft landing on Mars to collect and analyze the surface • System built with 20 year old technology • 34 million mile journey • Functioned correctly for over 5 years • Reliability was the most important requirement in this system

10. Mars Explorer • Failure points had to be understood and planned for • Redundant circuitry • Extra functionality • Extra processors • Special memory diagnostics • Hardware timers to reset system if it hangs

11. Sensors and Actuators Sensor: A device that measures or detects a real-world condition, such as motion, heat or light and converts the condition into an analog or digital representation. An optical sensor detects the intensity or brightness of light, or the intensity of red, green and blue for color systems. Actuator: A mechanism that causes a device to be turned on or off, adjusted or moved. The motor and mechanism that moves the head assembly on a disk drive or an arm of a robot is called an actuator.

12. ECU ACC WS driver WS passen. passenger detection ROS SAT SAT SAT SAT SAT SAT SAT driver detection BS BS BS BS BS Airbag System: Possible Sensors(Including Crash Severity and Occupant Detection) SAT = satellite with serial communication interface ECU = central airbag control unit (including accelerometers) ROS = roll over sensing unit WS = weight sensor BS = buckle switch

13. Kneebag Kneebag TB TB TB TB Interactionbag Airbag 2stage Airbag 2stage PBP PBP PBP PBP PBP Headbag Headbag Headbag Headbag Emergency Equipment Airbag System: Possible Actuators(Including Crash Severity and Occupant Detection) ECU TB = Thorax bag - The thorax bag is inflated within 12 thousands of a second; four times faster than a frontal airbag. The bag is inflated at a certain crash threshold PBP = pyrotechnical buckle pretensioner with load limiter - Seat belt buckle pretensioners employing explosive pyrotechnic gas generators as the power source ECU = central airbag control unit Near future airbag systems >> 10 actuator outputs

14. Automotive Seat Occupancy Detection DSP-based Embedded system (Processes Information) Seat w/ Fiber Sensing Technology • Airbag Deployment Decisions • (fire airbag? which airbags? • how much to inflate?, etc.)

15. A Generic embedded system • Processor • Just enough to get the job done • Register width is important • General purpose 32- bit and 64- bit • Embedded processors 8- and 16-bit • Memory • ROM (executable program) • RAM (data to manipulate) • Register width drives amount of memory

16. A Generic embedded system cont… • Development cost • Dependent of product • High volume products can stand for a higher development cost • Smaller volume is more sensitive to development cost • Number of units • Expected life time • Drives design decisions

17. A Generic embedded system • Reliability • Children's toys do not always have to work right • Space shuttle is a different story • Air France flight recorders located in Atlantic‎ - MOSCOW: Signals from the flight data recorders of the Air France jet that crashed into the Atlantic killing all 228 people on board have been located, ... • Beacons on the recorders send an electronic impulse every second for at least 30 days. The signal can be picked up from two kilometres away. French vessels involved in the search operation include a nuclear submarine with advanced sonar equipment and a research ship equipped with mini submarines.

18. Common design requirements

19. Functional requirements • Functional requirements describe the type of processing the system will perform  • Data Collection requirements • Sensoring requirements • Signal conditioning requirements • Alarm monitoring requirements • Direct Digital Control requirements • Actuator control requirements • Man-Machine Interaction requirements (Informing the operator of the current state of a controlled object for example

20. Temporal requirements • Embedded systems have many tasks to perform, each having its own deadline • Temporal requirements define the stringency in which these time-based tasks must complete • Minimal latency jitter • Minimal Error-detection latency • Temporal requirements can be very tight (for example control-loops ) or less stringent (for example response time in a user interface)

21. Dependability requirements • Reliability • considered at the system rather than the individual component level (emergent) • three dimensions to consider • Hardware reliability; probability of a hardware component failing • Software reliability; probability that a software component will produce an incorrect result • Operator reliability; how likely that the operator of a system will make an error

22. Dependability requirements cont… • Metrics used to determine system reliability • Probability of failure on demand; likelihood that the system will fail when a service request is made • Rate of failure occurrence; frequency of occurrence with which unexpected behavior is likely to occur • Mean Time to Failure; the average time between observed system failures.

23. Dependability requirements cont… • Safety: critical failure modes and what types of certification are required for the system • Maintainability: constraints on the system such as type of Mean Time to Repair (MTTR) • Availability:the probability that the system is available for use at a given time. • Security: unacceptable system behavior

24. Embedded processor alternatives Low cost Higher Off the shelf general Flexibility Purpose processor Off the shelf DSP, MCU Low power Embedded Core Processors DSP, MCU Higher speed Faster Time to market Hardwired Integrated Circuit (ASIC)

25. Embedded programming languages • C has become the language of embedded programmers • Advantages of C • Small • Easy to learn • Wide compiler support • Large body of experience • Processor independent

26. Embedded programming languages • C gives embedded programmers large degree of direct hardware control without sacrificing the benefits of a HLL • Produces relatively compact efficient code for a wide variety of processors • C++ and Ada are also good • Minimum assembly required (mostly)

27. Trends in embedded systems • Increasing code size • Migration to higher level language from assembly • As applications become more and more complex, programmers are transitioning to higher level languages for productivity reasons

28. Trends in embedded systems • Increasing reuse of pre-designed components • these include DSP chips as well as other microprocessors and microcontrollers • Migration to a core-based design • Systems becoming more complex and heterogeneous • There are more ASIC-based designs with high speed as well as high integration • Larger microprocessors are used with 32-bit processors becoming the norm