Real Time Embedded Systems Done by Lara Quadan

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 CPE-746 -JUST-Fall 2006 Quadan & Sawalha

Introduction n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Real-time Systems n n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

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

Application Areas n n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha n n n Computer/Communication products: ¨ Peripherals ¨ Fax machines Protection & security systems : ¨ Intruder Alarm ¨ Smoke/Gas detection Robotics

Control Theory n n 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). CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Embedded digital controlled systems n 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. n it is very important to consider the timing for the real-time digital controlled system. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Cruise Control n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

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

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

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

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

Cont. n Operating environment: closed indoor environments such as rooms. n 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. n n CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Hard Disk Drive Control n n n The disk rotates at a speed between 1800 and 7200 rpm. The head flies above the disk at a distance of less than 100 nm. Position accuracy is 1 micro meter. Move the head from track a to track b within 50 ms. Motor to actuate the arm to the desired location on the disk. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

Wireless Sensor Network Embedded System Sensor nodes scattered in a sensor field CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

Keck Astronomical Telescope n n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

n n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Auto-washing machines § The user will select the required washing program. § A set of sensor will monitor the washing process variables such as water level, temperature, and the rotation speed. Where the embedded controller will keep these values agree with the selected washing program. through out the washing time. 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Hard vs. Soft Real Time Systems n 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 n control systems for space probes and nuclear reactors. n refresh rates for video, or DRAM. n collision alert. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Cont. n 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). 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: n videoconferencing n stock price quotation systems n airline reservation systems n automatic teller 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. n 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 n 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. n Safety: Hard real-time systems are often safety critical. n 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 CPE-746 -JUST-Fall & Sawalha files is the 2006 key. Quadan issues. n

Characteristics of RTS n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

Real Time terminologies n n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Real Time terminologies n n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Operating System n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Real Time Operating System (RTOS) n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

n 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 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

RTOS n n Three groups ¨ Small, fast, proprietary kernels ¨ Real-time extensions to commercial operating systems ¨ Research operating systems Small, fast, proprietary kernels ¨ homegrown ¨ commercial offerings: n QNX, PDOS, p. SOS, VCOS, VRTX 32, Vx. Works ¨ To reduce the run-time overheads incurred by the kernel and to make the system fast, the kernel n has a small size n responds to external interrupts quickly n minimizes intervals during which interrupts are disabled n provides fixed or variable sized partitions for memory n management as well as the ability to lock code and data in memory n provides special sequential files that can accumulate data at a fast rate CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

RTOS To deal with timing constraints, the kernel n provides bounded execution time for most primitives n maintains a real-time clock n provides primitives to delay processing by a fixed amount of time and to suspend/resume execution ¨ Also, the kernel n 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. ¨ CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Examples of RTOS n Open source: ¨ e. Cos ¨ Fiasco (L 4 clone) [1] ¨ Free. RTOS ¨ Linux as of kernel version 2. 6. 18 ¨ Phoenix-RTOS ¨ Nut/OS [2] ¨ Prex ¨ RTAI ¨ RTEMS ¨ RTLinux ¨ SHa. RK [3] ¨ TRON Project ¨ Xenomai [4] CPE-746 -JUST-Fall 2006 - Quadan & Sawalha n Proprietary: ¨ ¨ ¨ ¨ ¨ Ardence RTX Chorus. OS DSOS ITRON Lynx. OS MQX RTOS [5] OS-9 OSEK/VDX PDOS Pike. OS p. SOS RMX RT-11 RTXC SINTRAN III Thread. X Vx. Works µn. OS - Be. OS - DNIX - emb. OS (Segger) - Micro. C/OS-II - Nucleus - OSEKtime - Phar Lap ETS - Portos - QNX - RSX-11 - RTOS-UH - Salvo RTOS [6] - Symbian OS - VRTX - Windows CE - UNIX-RTR

RTLinux n n 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! CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

RTLinux n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

RTLinux n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Vx. Works n n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

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

Examples on Software Subsystems n The software components of an embedded system can be diverse. ¨ Software running on a microprocessor core. n Written in a “High level language” ¨ Cooperative multi-tasking software running on one or more DSP processors n Largely written in Assembly code due compilers to a lack of high quality 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 ¨ CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Software Languages n n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Hardware Subsystems n n n n n 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 CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Hardware languages n n n Specifying connected gates concisely Originally targeted at simulation Discrete event semantics skip idle portions Mixture of structural and procedural modeling Hardware Languages: ¨ Verilog n Structural and procedural modeling n Four-valued vectors n Gate and transistor primitives n Less flexible, succinct ¨ VHDL n Structural and procedural modeling n Few built-in types; Powerful type system n Fewer built-in features for hardware modeling n More flexible, verbose ¨ System. C 1. 0, Cynlib: “VHDL/Verilog in C++” CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Hardware/Software Codesign n n 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 ¨ u. P, 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Examples of mixed hardwaresoftware embedded systems n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

Embedded System Design n n 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. CPE-746 -JUST-Fall 2006 - Quadan & Sawalha

References n n n n n Kopetz, H. , Real-Time Systems: Design Principles for Distributed Embedded Applications. Calton Pu, 1 B: RTE Concepts and Examples A Framework for Hardware-Software Co-Design of Embedded Systems, University of California, Berkeley. http: //www. ics. uci. edu/~rgupta/ics 212/w 2002/models. pdf http: //www. ics. uci. edu/~rgupta/ics 212/w 2002/intro. pdf http: //www. cs. unb. ca/courses/cs 4405/lectures/real-time. pdf http: //www. ece. cmu. edu/~koopman/des_s 99/real_time/#introduction http: //en. wikipedia. org/wiki/ http: //www. ics. uci. edu/~rgupta/iec/introduction/ CPE-746 -JUST-Fall 2006 - Quadan & Sawalha