Real Time Embedded Systems

1. CPE-746-JUST-Fall 2006 Quadan & Sawalha Real Time Embedded Systems Done by: Lara Quadan & Lina Sawalha Supervised by: Dr. Lo�ai Tawalbeh Computer Engineering Department Jordan University of Science and Technology

2. CPE-746-JUST-Fall 2006- Quadan & Sawalha Introduction Computer is entering all facets of life from home electronics to production of different products and material. Many of the computers are embedded and thus �hidden� for the user. So it is necessary to know about the control and characteristics of embedded real-time systems to implement reliable ones.

3. CPE-746-JUST-Fall 2006- Quadan & Sawalha Real-time Systems A real-time system is one in which the correctness of the computations not only depends on their logical correctness, but also on the time at which the result is produced. In other words, a late answer is a wrong answer. A real-time system consists of tasks under deadline constrains. Real-time systems maybe distributed systems, consisting of components that are physically distributed. These systems consists of multiple processing units and communication links.

4. CPE-746-JUST-Fall 2006- Quadan & Sawalha Functional Requirements Data Collection Sensors Signals Alarm Direct Digital Control Actuators Man-machine interaction

5. CPE-746-JUST-Fall 2006- Quadan & Sawalha Temporal Requirements Tasks may have deadline Minimal latency jitter Minimal error detection latency Timing requirements due to tight software control loops. Human interface timing requirements

6. CPE-746-JUST-Fall 2006- Quadan & Sawalha Application Areas Customer electronics: Cameras Camcorders Customer products: Dish washers Microwave ovens Cars: Anti-lock braking Engine control Drive-by-wire Planes: Stability Jet engine Fly-by-wire Military: Weapons Satellites Industrial process controllers Computer/Communication products: Peripherals Fax machines Protection & security systems : Intruder Alarm Smoke/Gas detection Robotics

7. CPE-746-JUST-Fall 2006- Quadan & Sawalha Control Theory A control system is an interconnection of components forming a system configuration that will provide a desired system response. Types of control : � Open-loop control: a system that utilizes a device to control the process without feedback. Thus the output has no effect upon the signal to the process. � Closed-loop control: A system that uses a measurement of the system output through sensors and compares it with the desired output (called feedback system).

8. CPE-746-JUST-Fall 2006- Quadan & Sawalha Embedded digital controlled systems When a digital controller (microprocessor/Microcontroller) is used in the embedded system to control the plant or process an analog/digital converter (A/D) is required as well as digital/analog converter (D/A) to interface the input/output controller digital signals with the analog signals from the other component in the system. it is very important to consider the timing for the real-time digital controlled system.

9. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cruise Control Regulate the speed of a car by adjusting the throttle: Input by the driver ? sets a speed and car maintains it. Measures the speed through device connected to the driver shaft. Hard real-time: driver shaft revolution event. Soft real-time: driver inputs, throttle adjustments.

10. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. Disturbances: road surface and grade, wind and obstacles. Input by the driver ? sets a speed and car maintains it. If the driver give a brake command to the car the cruise control system will be interrupted and the car speed will slow down or be stopped.

11. CPE-746-JUST-Fall 2006- Quadan & Sawalha Other car embedded systems

12. CPE-746-JUST-Fall 2006- Quadan & Sawalha Autopilot Objective function: to control the direction and speed of the plane. Outputs: actual direction and speed of the plane Control inputs: path markings and speed. Disturbances: wind, obstacles. subsystems: power system, engines, steering system, braking system, . . .

13. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont.

14. CPE-746-JUST-Fall 2006- Quadan & Sawalha Robot Vacuum cleaner

15. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. Operating environment: closed indoor environments such as rooms. Controlling System � Human : turn on and off the robot � Computer: Sensors: stairs and wall detection (IR sensors). Controls: robot location through controlling the robot speed and steering to follow the walls. Actuators: motors and wheels.

16. CPE-746-JUST-Fall 2006- Quadan & Sawalha Hard Disk Drive Control

17. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. For DVD system?

18. CPE-746-JUST-Fall 2006- Quadan & Sawalha Wireless Sensor Network Embedded System

19. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. Collection of sensor nodes in a field. Each node collects data and send it to a sink. The sink aggregates the data and send it to a main processing unit. Each sensor node can manipulate data using its own embedded microcontroller (microprocessor), transceiver and communication model.

20. CPE-746-JUST-Fall 2006- Quadan & Sawalha Keck Astronomical Telescope World largest telescope The main objective is to collect and focus starlight using a large concave mirror. The shape of the mirror determines the quality of the observed image. The diameter of the mirror is 10 m. The mirror is a mosaic of 36 hexagonal small mirrors. The 36 segments must be aligned so that the resulting mirror has the desired shape

21. CPE-746-JUST-Fall 2006- Quadan & Sawalha Behind each segment are three actuators applying forces at three points on the segment affecting its orientation. In the gap between every two adjacent segments a capacitor type sensors measuring the local displacement between segments. These displacements should be controlled to give the desired shape and direction for the mirror.

22. CPE-746-JUST-Fall 2006- Quadan & Sawalha Auto-washing machines

23. CPE-746-JUST-Fall 2006- Quadan & Sawalha Classifications of RT systems Hard vs. Soft systems Fail-safe vs. Fail operational Guaranteed-response vs. Best-effort Resource-adequate vs. Resource-inadequate Event-triggered vs. Time-triggered

24. CPE-746-JUST-Fall 2006- Quadan & Sawalha Hard vs. Soft Real Time Systems Hard RTS A RTS where the tasks have to be performed not only correctly but also on time. i.e. a catastrophic system failure can occur if the system is not responding on time. E.g., the aircraft turbulence (instability in the atmosphere) controller should respond on time, if not there will be a definite disaster. Other examples control systems for space probes and nuclear reactors. refresh rates for video, or DRAM. collision alert.

25. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. Soft RTS A RTS where the tasks have to be performed as fast as possible, but the tasks need not be finished within deadlines. I.e. It may go beyond specified deadlines without catastrophic failures (For example, if the video game is not responding on time, it�s only a delay where the user may not want to wait, but even then nothing awful is going to happen).

26. CPE-746-JUST-Fall 2006- Quadan & Sawalha Cont. Another e.g.: Laser printer: rated by pages-per-minute, but can take differing times to print a page (depending on the "complexity" of the page) without harming the machine or the customer. Task execution may also be timed-out: display updates, connection establishment. Other examples of Soft real time systems: videoconferencing stock price quotation systems airline reservation systems automatic teller

27. CPE-746-JUST-Fall 2006- Quadan & Sawalha Characteristics of RTS Response time: - hard real-time applications, milliseconds or less, preclude direct human intervention during normal operation and in critical situations. - Soft real-time and on-line systems are often in the order of seconds. Peak-load performance: - hard real-time system: the peak-load scenario must be well-defined, guaranteed to meet the specified deadlines in all situations.- soft-real time system, the average performance is important, and a degraded operation in a rarely occurring peak load case is tolerated Control of Pace: A hard real-time system must remain synchronous with all the state of the environment in all cases. This is in contrast to an on-line system, which can exercise some control over the environment in case it cannot process the offered load. Safety: Hard real-time systems are often safety critical. Size of Data files: Hard real-time systems have small data files and real-time databases. Temporal accuracy is often the concern here. Soft real time systems has larger databases so long-term integrity of large data files is the key issues.

28. CPE-746-JUST-Fall 2006- Quadan & Sawalha Characteristics of RTS Redundancy Type: If an error occurs in a soft real-time system, the computation is rolled back to a previously established checkpoint to initiate a recovery action. In hard real-time systems, recovery is of limited use.

29. CPE-746-JUST-Fall 2006- Quadan & Sawalha Common Misconceptions Misconceptions about Real-Time Systems [Stankovic'88] faster hardware implies all deadlines will be met real-time computing is merely fast computing RT systems are low-level coding done using ad-hoc methods. Fast is relative. More important that system is �fast enough", deterministic and predictable. Worst-case response times of interest rather than average-case. Scheduling theory, software design, formal methods and RTOS are changing things. It is important to note that hard versus soft real-time does not necessarily relate to the length of time available.

30. CPE-746-JUST-Fall 2006- Quadan & Sawalha Real Time terminologies Synchronous: events occur at predictable times in the flow-of-control. Asynchronous: interrupts Multitasking: The process of scheduling and switching the CPU between several tasks, a single CPU switches its attention between several sequential tasks. Multiple is like foreground/background with multiple backgrounds. Multitasking maximizes the utilization of the CPU and also provides for modular constructions of applications. Task: A task is called a Thread, is a simple program which thinks it has the CPU all to itself. Each task typically is an infinite loop that can be in any one of the three states: RUNNING, READY (-TO-RUN), BLOCKED. Resource: A resource is any entity used by a task. A resource can thus be an I/O device, such as a printer, a keyboard, or a display, or a variable, a structure, or an array.

31. CPE-746-JUST-Fall 2006- Quadan & Sawalha Real Time terminologies Shared Resource: A shared resource is a resource that can be used by more than one task. Each task should gain exclusive access to the shared resource to prevent data corruption. This is called Mutual Exclusion. For e.g., a global variable can be used by many tasks, or printer which could be shared by "n" users. Critical Section of Code: Also called Critical Region, is code that needs to be treated indivisibly; once the section of code starts executing, it must not be interrupted. To ensure this, interrupts are typically disabled before the critical code is executed and enable when the critical code is finished. Reentrancy: A reentrant function can be used by more than one task without fear of data corruption. a reentrant function can be interrupted at any time and resumed at a later time without loss of data. Reentrant functions either use local variables (i.e. CPU registers or variables on the stack) or protect data when global variables are used.

32. CPE-746-JUST-Fall 2006- Quadan & Sawalha Operating System Real-time operating systems must provide support for: Guaranteeing real-time constraints. Supporting fault tolerance and distribution. Time constraint resource allocations and scheduling. Time constraint end-to-end communications.

33. CPE-746-JUST-Fall 2006- Quadan & Sawalha Real Time Operating System (RTOS) Fundamental requirements for an RTOS The OS behavior must be predictable The OS must be multithreaded and preemptive. The OS must support thread priority. The OS must support predictable thread synchronization mechanisms. Additional Requirements: The maximum time that device drivers use to process an interrupt, and specific IRQ information relating to those device drivers, must be known. The interrupt latency (the time from interrupt to task run) must be predictable and compatible with application requirements

34. CPE-746-JUST-Fall 2006- Quadan & Sawalha Kernel Is the core program of the Operating System, and determines its behavior Is responsible for System Resources and for �context switch�. Also responsible for task scheduling. In RTOS since the size of the kernel is small, its also referred to as Micro Kernel. Kernel types Microkernel - scheduler Kernel - a microkernel with intertask synchronization Executive - a kernel that includes privatized memory blocks, I/O services, and other complex issues. Most commercial realtime kernels are in this category. Operating system - an executive that also provides generalized user interface, security, file management system, etc.

35. CPE-746-JUST-Fall 2006- Quadan & Sawalha RTOS Three groups Small, fast, proprietary kernels Real-time extensions to commercial operating systems Research operating systems Small, fast, proprietary kernels homegrown commercial offerings: QNX, PDOS, pSOS, VCOS, VRTX32, VxWorks To reduce the run-time overheads incurred by the kernel and to make the system fast, the kernel has a small size responds to external interrupts quickly minimizes intervals during which interrupts are disabled provides fixed or variable sized partitions for memory management as well as the ability to lock code and data in memory provides special sequential files that can accumulate data at a fast rate

36. CPE-746-JUST-Fall 2006- Quadan & Sawalha RTOS To deal with timing constraints, the kernel provides bounded execution time for most primitives maintains a real-time clock provides primitives to delay processing by a fixed amount of time and to suspend/resume execution Also, the kernel performs multitasking and intertask communication and synchronization via standard primitives such as mailboxes, events, signals, and semaphores. For complex embedded systems, these kernels are inadequate as they are designed to be fast rather than to be predictable in every aspect.

37. CPE-746-JUST-Fall 2006- Quadan & Sawalha Examples of RTOS Open source: eCos Fiasco (L4 clone) [1] FreeRTOS Linux as of kernel version 2.6.18 Phoenix-RTOS Nut/OS [2] Prex RTAI RTEMS RTLinux SHaRK [3] TRON Project Xenomai [4] Proprietary: Ardence RTX - BeOS ChorusOS - DNIX DSOS - embOS (Segger) ITRON LynxOS - MicroC/OS-II MQX RTOS [5] - Nucleus OS-9 - OSE OSEK/VDX - OSEKtime PDOS - Phar Lap ETS PikeOS - Portos pSOS - QNX RMX - RSX-11 RT-11 - RTOS-UH RTXC - Salvo RTOS [6] SINTRAN III - Symbian OS ThreadX - VRTX VxWorks - Windows CE �nOS - UNIX-RTR

38. CPE-746-JUST-Fall 2006- Quadan & Sawalha RTLinux Real-Time Linux (now part of FSMLabs Inc.) that is suitable for Real-Time applications. Its view is that the application system can be split into two parts Real-time Non real-time With this approach, it splits the applications to run on either the Linux kernel, or a real-time kernel!

39. CPE-746-JUST-Fall 2006- Quadan & Sawalha RTLinux Between the real and non-real parts communication is performed through FIFOs called RT-FIFOs. These FIFOs are: Locked to memory in kernel space. FIFOs appear as devices to Linux user processes. Reads and writes are non-blocking and atomic.

40. CPE-746-JUST-Fall 2006- Quadan & Sawalha RTLinux RTLinux eliminates the problem of the kernel blocking interrupts by replacing HW interrupts by SW emulated interrupts. Thus, the RT kernel intersects all interrupts! If an interrupt is to let a RT task execute, then the RT kernel pre-empts any general application and runs the RT task. Flags are used to emulate interrupt disabling.

41. CPE-746-JUST-Fall 2006- Quadan & Sawalha VxWorks Monolithic Kernel Reduced run-time overhead, but increased kernel size compared to Microkernel designs Supports Real-Time POSIX standards Common in industry Mars missions Honda ASIMO robot Switches MRI scanners Car engine control systems

42. CPE-746-JUST-Fall 2006- Quadan & Sawalha Software vs. Hardware Hardware Fast Power-efficient Used for performance and security Software Flexible Reusable

43. CPE-746-JUST-Fall 2006- Quadan & Sawalha Examples on Software Subsystems The software components of an embedded system can be diverse. Software running on a microprocessor core. Written in a �High level language� Cooperative multi-tasking software running on one or more DSP processors Largely written in Assembly code due to a lack of high quality compilers An RTOS kernel running on the microprocessor core and/or DSP core Control Processes running on a microcontroller User interface modules running on the microprocessor Devise drivers for interface protocols e.g. TCP/IP, ATM

44. CPE-746-JUST-Fall 2006- Quadan & Sawalha Software Languages Specifying machine code concisely Sequential semantics: Perform this operation Change system state Raising abstraction: symbols, expressions, control-flow, functions, objects, templates, garbage collection. C/C++/Java Real Time Operating Systems: Adds concurrency, timing control

45. CPE-746-JUST-Fall 2006- Quadan & Sawalha Hardware Subsystems Microprocessor cores DSP cores Field Programmable Gate Arrays (FPGAs) Application specific integrated circuits (ASICs) standard cell/synthesized deigns custom ICS Memory RAM, ROM, PROM, ... Conten addressable memory (CAM) Specialized DRAMs, multi-bank memories, System Bus structures & interfaces I/O interfaces Others

46. CPE-746-JUST-Fall 2006- Quadan & Sawalha Hardware languages Specifying connected gates concisely Originally targeted at simulation Discrete event semantics skip idle portions Mixture of structural and procedural modeling Hardware Languages: Verilog Structural and procedural modeling Four-valued vectors Gate and transistor primitives Less flexible, succinct VHDL Structural and procedural modeling Few built-in types; Powerful type system Fewer built-in features for hardware modeling More flexible, verbose SystemC 1.0, Cynlib: �VHDL/Verilog in C++�

47. CPE-746-JUST-Fall 2006- Quadan & Sawalha Hardware/Software Codesign Most systems and mixed between hardware and software. Traditional Design SW and HW partitioning is decided at an early stage, and designs proceed separately from then onward. CAD today addresses synthesis problems at a purely hardware level: efficient techniques for data-path and control synthesis down to silicon. ECS use diverse (commodity) components uP, DSP cores, network and bus interfaces, etc. "New fangled" Codesign A flexible design strategy, wherein the HW/SW designs proceed in parallel, with feedback and interaction occurring between the two as the design progresses. Final HW/SW partition/allocation is made after evaluating trade-offs and performance of options.

48. CPE-746-JUST-Fall 2006- Quadan & Sawalha Examples of mixed hardware-software embedded systems Embedded controllers for reactive real-time applications are implemented as mixed software-hardware systems. These controllers utilize Micro-processors, Micro-controllers and Digital Signal Processors but are neither used nor perceived as computers. Generally, software is used for features and flexibility, while hardware is used for performance. Some examples of applications of embedded controllers are: Consumer Electronics: microwave ovens, cameras, compact disk players. Telecommunications: telephone switches, cellular phones. Automotive: engine controllers, anti-lock brake controllers. Plant Control: robots, plant monitors.

49. CPE-746-JUST-Fall 2006- Quadan & Sawalha Embedded System Design Modelling the system to be designed, and experimenting with algorithms involved; Refining (or �partitioning�) the function to be implemented into smaller, interacting pieces; HW-SW partitioning: Allocating elements in the refined model to either (1) HW units, or (2) SW running on custom hardware or a general microprocessor. Scheduling the times at which the functions are executed. This is important when several modules in the partition share a single hardware unit. Mapping (Implementing) a functional description into (1) software that runs on a processor or (2) a collection of custom, semi-custom, or commodity HW.

50. CPE-746-JUST-Fall 2006- Quadan & Sawalha Kopetz, H. , Real-Time Systems: Design Principles for Distributed Embedded Applications. Calton Pu, 1B: RTE Concepts and Examples A Framework for Hardware-Software Co-Design of Embedded Systems, University of California, Berkeley. http://www.ics.uci.edu/~rgupta/ics212/w2002/models.pdf http://www.ics.uci.edu/~rgupta/ics212/w2002/intro.pdf http://www.cs.unb.ca/courses/cs4405/lectures/real-time.pdf http://www.ece.cmu.edu/~koopman/des_s99/real_time/#introduction http://en.wikipedia.org/wiki/ http://www.ics.uci.edu/~rgupta/iec/introduction/ References