COMP3221/9221: Microprocessors and Embedded Systems COMP3221: Microprocessors and Embedded Systems Lecture 31: Embedded Systems cs3221

COMP3221/9221: Microprocessors and Embedded Systems

COMP3221: Microprocessors and Embedded Systems

Lecture 31: Embedded Systems

http://www.cse.unsw.edu.au/~cs3221

Lecturer: Hui Wu

Session 2, 2005


Overview

• What is an embedded system?

• Characteristics of embedded systems

• Embedded system requirements


Embedded Systems

An embedded system

• is a combination of hardware and software to perform a specific function;

• is part of a larger system;

• works in a reactive and time-constrained environment.

Characteristics of Embedded Systems• Application specific

An embedded system performs a single or fixed set of functions;

All functions are known a priori before the system design begins.

The fixed functionality provides opportunities for design optimization.

Application specific processor design can be a significant component of some embedded systems

Advantages

Customization yields lower area, power, cost and higher performance.

Disadvantages

Higher hardware/software development overhead, resulting in longer time-to-market.

• Strict design constraints

performance, timing, power, area, cost, reliability etc.

Characteristics of Embedded Systems (Cont.)

• Multiple heterogeneous processing units

General processor, ASIC (Application Specific Integrated Circuit) , ASIP (Application Specific Instruction set Processor), DSP (Digital Signal Processing processor) etc.

• Reactive

Embedded systems constantly interact with their environment, taking in data from sensors and/or other input devices and making appropriate responses.

• Real-time

Embedded systems interact with their environments in a timely manner.

• Parallel and distributed computing

Many embedded systems use parallel/distributed architecture where multiple processing units are tightly or loosely coupled.


Examples of Embedded Systems

• Consumer electronics, e.g., cellular phones, personal digital assistants, interactive game boxes, cameras, camcorders, ....

• Consumer products, e.g., washers, microwave ovens, ...

• Automobiles (anti-lock braking, engine control, ...)

• Industrial process controllers & avionics/defence applications

• Computer/Communication products, e.g., printers, FAX machines, ...


Traditional Embedded Systems Design: Major Procedures

• Modelling

Specifying the behaviours of the target embedded system.

• Hardware-software partitioning

Partitioning the specifications into either hardware components or software components.

Hardware components are implemented in co-processors.

Software components run on custom hardware or a general microprocessor.

• Hardware design and software design

Hardware design includes co-processor design, interfaces etc.

Software design includes interrupt handlers, task scheduler etc.


Traditional Embedded Systems Design: Major Procedures (Cont.)

Modelling

Hardware-software partitioning

Hardware design Software design


Problems with Traditional Embedded Systems Design

• The precise information (execution time etc) about each task is not available at the partitioning stage.

• Designers have to use estimated values in partitioning, leading to bad partitioning and therefore bad design.

• How to solve this problem?

Use hardware-software co-design.


What Is Hardware-Software Co-design?

• The hardware/software designs proceed in parallel, with feedbacks and interactions occurring between the two as the design progresses.

• An multi-objective function of cost, area, power etc is used to find an optimal design.


Goals of Embedded System Design

• Reduce time-to-market.

• Produce an optimal design which minimize the multi-objective function of cost, area, power etc.

New design methodology and CAD tools for automating embedded system design are needed.

CAD today addresses synthesis problems at a purely hardware level:

efficient techniques for data-path and control synthesis down to silicon.


Disciplines Involved in Embedded System Design

• Application domain (Signal processing, process control, machine control, robot, ...).

• Software engineering

How to build a correct and reliable embedded system?

Software reuse?

• Programming Languages and Compilers

How to reduce the execution time of each task?

How to reduce the power consumption of processors and memory?


• Operating Systems

How to schedule tasks such that all timing constraints are satisfied?

How to schedule tasks such that the processor power consumption is minimized?

• VLSI (computer aided) design

How to minimize the area and maximize the performance for a co-processor?

How to minimize the power consumption of a co-processor?

Disciplines Involved in Embedded System Design (Cont.)


• Parallel/Distributed systems

Many embedded systems use parallel/distributed architecture where the multiple processors are tightly coupled or loosely coupled. Many issues exist.

Task scheduling;

Resources sharing etc.

• Real-time systems (Hard & soft real time systems)

How to specify and satisfy timing requirements?

How to share resource such that timing constraints are still satisfied?

Disciplines Involved in Embedded System Design (Cont.)


Embedded System Requirements

• Functional requirements

• Timing requirements

• Dependability requirements

Functional Requirements

• Data collection

Sensors

AD converters

Signal conditioning etc

• Direct digital control

Actuators

• Man-machine interface

Informs the operator of the current state of the controlled object

Assists the operator in controlling the system.


Timing Requirements

• Tasks Release times and deadlines

• Minimal task distance

• Maximal task distance

• Task Periods

• Minimal error detection latency

• Minimal latency jitter etc.

Timing constraints are often imposed on tasks. Typical timing constraints include:

• Release time: A task cannot be executed before its release time.

• Deadline: A task is required to finish by its deadline.

• Minimal distance: The distance between two tasks is required to be greater than a specified value.

The distance is defined to be the difference of the start time of the other task completed later and the completion time of the task completed earlier.

• Maximal distance: The distance between two tasks is required to be less than a specified value.

Timing Requirements (Cont.)


• Period: A periodic task must be executed periodically. For example, if the period of a task is 5, it must be executed and completed every 5 time units.

…

0 2 5 7 10 12

T1 T1 T1

Figure 1: A periodic task T1 has a period of 5 and a worst-case execution time of 2.



• Hard Timing constraints: Miss of any hard timing constraints may cause catastrophes e.g., control systems for aircraft/space probes/nuclear reactors.

• Soft timing constraints: The violation of soft timing constraints only causes performance degradation. e.g., game box.

• Embedded systems may contain both hard and soft timing constraints.

• Task scheduler is responsible for satisfying all timing constraints.


Consider an embedded system with a single processor and a set of 3 tasks T1, T2 and T3 with the following attributes:

• T1 is a periodic task with a period of 4 and a worst-case execution time of 2;

• T2 is a periodic task with a period of 5 and a worst-case execution time of 2;

• T3 is a non-periodic task with a release time of 0, a deadline of 20 and a worst-case execution of 2.

T1 T2 T1T1 T1

0 2 4 6 8 10 12 14 16 18 20

T1T2 T2 T3 T2


Dependability Requirements

• Reliability

Number of failures per hour or Mean-Time-To-Failure (MTTF) in hours.

• Safety

critical failure modes

certification

• Maintainability

Mean-Time-To-Repair (MTTR).

• Availability

A = MTTF / (MTTF + MTTR)

• Security

Major Components in Embedded Systems

• Microprocessors/microcontrollers, co-processors, DSP cores, ASICs, ASIPs, FPGAs (Field Programmable Gate Arrays), memory (RAM, ROM, FLASH, EEPROM) and buses.

• Data acquisition and processing

• Communication

• System logic and control

• Interfaces

• Auxiliary units

display

storage

monitoring and protection

test and diagnosis.

— From LSI Logic web Page

Courtesy: R. Gupta, UC Irvine

Example Embedded System (I): DVD

— From Siemens web page

Courtesy: R. Gupta, UC Irvine

Example Embedded System (II): Dryer


Reading Material

1. Chapter 1 in Embedded Systems Design: An Introduction to Processes, Tools, and Techniques by Arnold S. Berger.

2. S. Edwards, L. Lavagno, E. Lee, A. Sangiovanni-VincentelliDesign of Embedded Systems: Formal Methods, Validation and Synthsis. Proceedings of the IEEE, vol. 85 (no.3) , March 1997, p366-290.

Documents

COMP3221/9221: Microprocessors and Embedded Systems COMP3221: Microprocessors and Embedded Systems Lecture 31: Embedded Systems cs3221