Embedded systems structure

Embedded Systems Structure
Amr Ali Abdel-Naby
Embedded Systems Developer

+2-012-3600-207

Embedded Systems Structure

Amr Ali AbdelNaby@2010


Outline
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Composition of Embedded Systems
Processor
System Bus
Memory Devices
Peripherals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Part I: Embedded Systems
Structure

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•
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Composition of Embedded Systems
Processor
System Bus
Memory Devices
Peripherals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


What is an Embedded System?
• A system composed of HW + SW to perform a
dedicated function.
• On average, a human being meets 100s of
embedded systems daily

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Embedded System Components
Application SW

SW

Operating System

Device Drivers

H
W

Processor

Amr Ali Abdel-Naby@2010

Memory
Devices
Embedded Systems Structure

I/O Devices


Part I: Embedded Systems
Structure
•
•
•
•
•

Composition of Embedded Systems

Processor
System Bus
Memory Devices
Peripherals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


The Processor
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The core of a digital system
AKA CPU
Performs arithmetic, control, data, and I/O operations
A small IC that embeds everything a CPU needs is
called a microprocessor.
• Nowadays, this IC is called a SOC

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


The Processor Structure
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Registers
ALU: Arithmetic Logic Unit
CU: Control Unit
Internal Bus

Registers

Internal Bus

ALU

Amr Ali Abdel-Naby@2010

Embedded Systems Structure

CU


Registers
• Temporal storage inside the CPU
o

Flip-flops + latches

• General purpose register
o

Carry out program or data processing

• Control register
o
o

Controls the program or the processor
Program Counter (PC), …

• Status/flag register
o

Shows the current state of the processor

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


ALU
• Arithmetic operations
o

+, -, …

• Logical operators
o

AND, OR, …

• Writes operation results to the status register or the
flag register
o

Carry occurrence, overflow occurrence, …

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


CU
• Controls the internal data flow to decode and
execute an instruction
Program Counter

Memory Device

Instruction Register
Instruction Decoder
Control Signal Generator
Amr Ali Abdel-Naby@2010

Embedded Systems Structure

Instruction


Processor Bus

• A bus is a path that connects the various devices of
a system
• Internal bus
o

Between registers and ALU

• External bus
o
o
o
o

Between I/O devices, memories, and CPU
Data bus: transfers data
Address bus: transfers address information
Control bus: transfers control signals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Pipeline
• Continuous and parallel streaming of instructions to
the CPU
CPU
W/O
Pipeli
ne

CPU
+
Pipeli
ne

Fetch 1

Execute 1

Fetch 1

Execute 1
Fetch 2

Fetch 2

Execute 2
Fetch 3

Amr Ali Abdel-Naby@2010

Execute 2

Execute 3

Embedded Systems Structure

Fetch 3

Execute 3


Various Processors
• i386
o
o

Long history
PCs

• ARM
o
o

Simple
Cell phones and PDAs

• PowerPC
o

Networking capabilities

• M68K
o

Network devices and portable terminals

• MIPS
o

High speed network devices

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


MCU, MPU, and SoC
• System on Chip (SoC)
o
o
o

Several semiconductors integrated into a single chip
Modern CPUs are in SoC forms
The whole system is integrated on a single chip
 SW + HW

• MCU, MPU
o

Another naming of an SoC
 Depends on vendor

Amr Ali Abdel-Naby@2010

Embedded Systems Structure

Program
• A list of acceptable processor instructions
• Designed to achieve a specific result

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Machine Code and Assembly
Language
• Machine code
o
o
o

1’s and 0’s only
Understood by processor only
Inconvenient to write a program with

• Mnemonic code
o

Machine code converted to symbols understood by
programmers

• Assembly language
o

Mnemonic code + pseudo instructions to improve programs

readability

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


C/Cs of Assembly Language
• Pros
Better readability and understanding compared to machine
code
o Easier to debug and maintain compared to machine code
o

• Cons

Knowledge of processor internal structure and HW is
necessary
o Different assembly for different processors
o

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Assembler and Assemble
• Assembler
o

A program that converts assembly language into machine
code

• Assemble
o

The process of converting assembly language into machine
code

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Instruction
• Instruction = Op Code + Operand
o
o

Op Code is an action taken by a processor
Operand is the target the Op Code should take action to

ADD A,B,C
Op Code: ADD
Operands: A, B, C
Symantec: Add register B and register C and put result in register
A

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Types of Processors
• Complex Instruction Set
Computers (CISC)
o
o
o
o

1960s
Memory referencing
operations
Complicated
Low performance

Amr Ali Abdel-Naby@2010

• Reduced Instruction Set
Computers (RISC)
o
o
o
o

1950s
Load/Store
Simple
High performance

Embedded Systems Structure


Part I: Embedded Systems
Structure
•
•
•
•
•

Composition of Embedded Systems
Processor
System Bus
Memory Devices
Peripherals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


System Bus Architectures
• Von-Neumann

CPU

• Harvard

CPU
Instruction/Data
Memory

Instruction
Memory

Data Memory

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Part I: Embedded Systems
Structure
•
•
•
•
•

Composition of Embedded Systems
Processor
System Bus
Memory Devices
Peripherals

Amr Ali Abdel-Naby@2010

Embedded Systems Structure


Types of Memories
Types

Volatile
Memory

NonVolatile
Memory

Speed

Cost

Use

SRAM

Several ns, Fast

High

Cache

DRAM

Tens of ns

Low

Main memory

EEPROM

Tens of ns

High

Small size data or
program storage

NAND

Tens of ns

Low

Data Storage

NOR

Tens of ns

High

Program and Data
Storage

Flash

Amr Ali Abdel-Naby@2010

Embedded Systems Structure

C/Cs

Read and WRITE
with block units,
High Capacity