Embedded Systems

Introduction 09/10

Embedded Systems 16-5147

Alan Holloway – contact: a.f.holloway@shu.ac.uk– Room 9323 Furnival

• 12 × 1 Hour Lectures • 12 × 2 Hour Labs (staffed for 1 Hours)• 100% Coursework

– formative series of lab tutorials (10%)– 5 × Homework questions ( 2% each ) – major assignment (80%)

Resources

• All course information can be found at www.aholloway.co.uk follow link for this unit– Lecture notes– Sample programs– Reading list– Software (available free)

What is an embedded system?

• An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions

•Washing machine runs programs•Open water valve•Heat water•Start spin•etc etc….

•Do we need a PC running windows Vista to do this ?

Will I ever need to use one?

• Over 4 billion 8-bit microcontrollers were sold in 2006 alone

• the world's population is estimated to be about 6.756 billion

• Average car contains >50 microcontrollers• Electrical, electronic, control, robotics,

computer engineer - Yes you will

Embedded Systems

• Microprocessor Systems• Microcontrollers• ARM7 core Processor Family

– specifically NXP LPC2368 microcontroller– Many others are available 8051, PIC, AVR etc

• C Programming will be used throughout– ARM Realview MDK - 'C' compiler & other tools– u-Vision Integrated Development Environment

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Microprocessor system

• CPU• Memory – ROM and RAM• Input – various• Output - various

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Bus system

• Devices connect to microprocessor via bus system (often called the memory bus)

• A devices connected to bus must be tri-state devices– only one device is activated at a time

• Consists of 3 bus types– Address bus– Data bus– Control bus

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clock

address bus

data bus

chip enable signals

readwrite

uP ROM I/ORAM

CE CECE

OE WR OE OEWR

Additional devices

Microprocessor System Structure

ad

address decoder

reset

Bus operations

• Read • Write• Each read/write operation is made up of a

number of clock cycles or T states• Each machine instruction is made up of one or

more read and/or write operations• This is why we shouldn't compare

microprocessors simply based on clock speed

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Address Bus• Unidirectional and generated by microprocessor• Number of address lines determines number of address

locations • Addressable locations = 2^a where a is the number of

address lines

ROM

RAM

I/O

0000H

E000H

3FFFH

E00FH

7FFFH

FFFFH

6000H

MemoryAddress

Totalmemory space

d bits

2a - 1

01

Memory Map :A memory map shows the position of devices within the whole of the addressable area

memory addresses

Data Bus

• Bi-directional• Usually matches the word length of the

microprocessor • Usually a multiple of 8 • We talk of 8-bit, 16-bit , 32-bit and 64-bit

processors which refers to the normal word length of the microprocessor

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Control bus

• Consists of potentially many signals. Typically:-– Read– Write– Could be single signal - Read/notWrite line– Interrupt control– Bus control signals for DMA (Direct Memory

Access)

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Microprocessr

• CPU – Central Processing Unit– ALU – Arithmetic Control Unit– Registers– Control Unit

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Microprocessor Registers

• General purpose registers• Accumulator – used in conjunction with ALU –

often found on 8-bit microprocessors• Status or Flag Register – indicate result of last

instruction executed• Program counter(PC) or Instruction Pointer• Stack Pointer (SP)• Special registers – Instruction and memory

address register

The Fetch – Execute cycle• Fetch

– memory read cycle– place in instruction register and decode

• Execute– may involve additional read and/or write cycles

• Often the whole Fetch-Execute cycle is carried out through a pipeline operation involving several stages.– 5 stages are often used (IF, ID, RR, EX, WB)– The Pentium 4 has 20 stages– The ARM 7 has 3 stages

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Pipeline - Natural assembly line• Example

– Alan (A) Barry (B) & Chris (C) each have a load of clothes

• Washer takes 30 mins

• Dryer takes 30 mins

• Ironing takes 30 mins

A B C

Sequential - non pipelined

30 30 30 30 30 30 30 30 30

A

B

C

7pm 11.30pm

Total for 3 Loads is 4.5 Hours

Pipelined

• Total for 3 loads pipelines 2.5 hours

30 30 30 30 30 30 30 30 30

A

B

C

7pm 11.30pm

Pipelines

• Does not speed up 1 task - increases overall throughput

• Multiple tasks operate simultaneously using separate resources

• Limited by speed of slowest resource

ARM7 Pipeline• The pipeline has hardware-independent stages that execute one

instruction while decoding a second and fetching a third. The pipeline speeds up the throughput ofCPU instructions so effectively that most ARM instructions can be executed in a single cycle.

• The pipeline works most efficiently on linear code.

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CPU operation

• On reset – PC is loaded with a value, typically 0• Fetch – execute cycle

– Fetch instruction • memory read cycle using PC (program counter)• place in instruction register and decode• increment PC ready for next fetch

– Execute instruction• often involves additional read and/or write cycles to read

operands and possibly write back results• could modify PC – causes flow of program execution to

change

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CPU Architecture

• Two basic types– Von Neumann

• One memory space for instructions and data• Therefore one single memory bus structure

– Harvard• Separate instruction and data spaces• Therefore separate memory buses – parallel operation

and therefore faster operation• Can have different address and data bus widths

optimised for each bus

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Basic microprocessor system

• Von Neumann Architecture

Reset

Oscillator

Clock

Memory (Instructions & Data) and Input/Output

Read

Write

Address

Data

Microprocessor

Power on & manual reset

D0-dy

A0-Ax

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Harvard Architecture

Program Memory

Data Memory & I/O

Read

Write

Address

Data

Microprocessor

d0-dn

Address

Read

Instruction

I0-Iw

A0-AxA0-Ay

Microcontroller

• A microcontroller is the integration of – microprocessor– memory

• ROM types – commonly flash PROM• RAM – Static ram

– peripherals• parallel input and output(digital I/O)• Timers and Counters• Serial input and output (UART, USART, SPI etc.) • Analogue to digital converters• PWM, CAPCOM registers, DACs etc.etc.

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What is an Embedded Computer System• Special purpose computer – usually with one

specific task or application.• Usually embedded in a device which often

has other electronic and mechanical parts• Usually optimised for the specific task• Has the usual basic computer components –

CPU, memory, inputs & outputs

Examples• consumer appliances

– tv's, mp3 players, dvd's, washing machines etc.

• automotive applications– engine management, anti-lock braking

• computer peripherals– hard disk controllers, routers, switches

• medical equipment– scanners, blood analysers

• telecoms– mobile phones

• aerospace – satellite control systems, avionics

Some Characteristics

• Very simple to very complex applications • Often single application

– but concurrent operation• Could be real-time (hard and soft)• Program is normally stored in ROM – called

firmware – flash ROM commonly• Could be critical applications • Interfacing with other devices via peripherals• Require a range of development tools –

hardware and software• May use operating system (RTOS)

Constraints

• Physical size• Weight• Power usage• Performance – throughput and/or response

time• Cost

Resulting in -

• limited space• limited processing power

– 8-bit processor• limited memory RAM & ROM

– only Ks of memory not Ms• schemes to limit power consumption

– low power modes– sleep– standby

• determinism – needed for RT guarantee

Microprocessor vs Microcontroller vs Soc vs FPGA

• uP – General purpose– external memory and peripherals– connected by a memory bus

• uC– uP integrated with memory and peripheral

interfaces– families of uC all with same uP but varying

amounts and types of memory and interfaces.

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Microcontroller (µC) vs. Microprocessor (µP)• µC intended as a single chip solution, µP requires

external support chips (memory, peripheral interfaces etc.)

• µC has on-chip non-volatile memory for program storage, µP does not.

• µC has more interface functions on-chip (serial interfaces,Analog-to-Digital conversion, timers, etc.) than µP

• General purpose µPs are typically higher performance (clock speed, data width, instruction set, cache) than µCs

• However the division between some µPs and some µCs becoming increasingly blurred.

FPGA/PLD• A field-programmable gate array is a semiconductor device

containing programmable logic components called "logic blocks", and programmable interconnects. Logic blocks can be programmed to perform the function of basic logic gates such as AND, and XOR, or more complex combinational functions such as decoders or simple mathematical functions. In most FPGAs, the logic blocks also include memory elements, which may be simple flip-flops or more complete blocks of memory

Microprocessor vs Microcontroller vs SoC vs FPGA

• SoC – System on a chip• FPGA – Field

Programmable Gate Array

Microcontroller-based System-on-a-Chip

Core

Rest of FPGA contains standard

logic