Introduction to embedded systems

Introduction to Embedded Systems

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Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems

Course Objective
After completing this course, you will answer:
What is an embedded systems?
What is an embedded hardware?
What is embedded software?
What are the embedded systems development tools?

Course Notes
Set your cell phone to vibrate.
I assume you know computer architecture.
Ask any time.

Course References
Embedded Systems Architecture 2 nd Edition, Tammy Noergaard
Introduction to Real-Time Operating Systems, by David Kalinsky
http://en.wikipedia.org/

Course Outline
Introduction
Embedded Hardware
Embedded Software
Embedded Development Tools

What is a Computer System?
A programmable machine that executes a sequence of operations to perform certain functions.
A computer system consists of:
Hardware
Software
Examples include:
Servers
PCs
Embedded systems
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Software Hardware

Hardware
The physical component of a computer system.
HW is:
Harder to develop
Customized to a specific application
Of better performance in high-speed systems
Examples include:
Processor
Memories
IOs

Software
The non-physical part of a computer system.
SW is:
Highly configurable
Faster to develop
Easier to update
Cheaper to develop
Of limited performance by the HW it runs on
Examples include:
Applications
Operating systems

What is a General Purpose System?
A computer system that can do many functionalities depending on:
Available hardware
Installed programs
Examples include:
PCs
Servers

What is an Embedded System?
A special purpose computer system that can perform a single or few functionalities.
Functionalities are done by dedicated HW and SW with limited resources.
On average, a person interacts with 100s of embedded systems on daily basis.
Embedded systems are of high diversity.

Embedded Systems Examples Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems

Characteristics of Embedded Systems - Dependability
Reliability
Maintainability
Availability
Safety
Security

Characteristics of Embedded Systems - Efficiency
Energy
Code size
Run-time
Weight
Cost

Characteristics of Embedded Systems - Dedication
Dedicated user interface
No mouse, no screen, no keyboard…
Dedicated towards an application
Knowledge at design time can be used to minimize resources and maximize robustness

Characteristics of Embedded Systems – Meeting Real-Time Constraints
React to stimuli within a time interval dictated by the system specs
Right answers arriving too early or too late are wrong.
An embedded system can be a:
Hard real-time system
Firm real-time system
Soft real-time system

Characteristics of Embedded Systems – Connection to a Physical Environment
Through sensors and actuators
Hybrid systems
Analog, digital, mechanical…
Typically, embedded systems are reactive.

Embedded Versus General Purpose Systems
Embedded
Few applications
A part of a bigger system
Not programmed by end users
Harder to develop
General Purpose
Board class of application
Standalone or integrated in parallel with other systems
End users programmable
Easier to develop

Embedded Systems Architecture Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Device Drivers Operating Systems Middleware Application SoC Memories Peripherals

Exercise 1: Characterize an Embedded System
Goal: Identify embedded systems characteristics
Each group of 2 persons should:
Pick an embedded system
Identify its characteristics
Time: 15 minutes

Course Outline
Introduction
Embedded Hardware
Embedded Software

CPU, Processor, and SoC Amr Ali Abdel-Naby@2011 Introduction to STM32 STM32 SoC

Central Processing Unit
AKA CPU
Core of most of digital systems
Performs arithmetic, control, data, and IO operations

CPU Structure
Registers
Internal bus
Address
Data
Control
CU: Control Unit
ALU: Arithmetic and Logic Unit
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems CU Registers ALU Internal Bus

Registers
Temporal storage inside the CPU
Flip-flops and latches
A register can be:
A general purpose register
Carry out program or data processing
A control register
Controls the program or the CPU
A status/flag register
Shows the current state of the CPU

ALU
Carries on:
Arithmetic operations
+, -, …
Logic operations
AND, OR, SHIFT…
Operates and stores results in general registers
Stores operation status in flag/status registers
Carry occurrence, overflow occurrence…

CU
Controls the internal flow to fetch, decode, and execute an instruction
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Instruction Program Counter Memory Device Instruction Register Instruction Decoder Control Signal Generator

Pipelining
Continuous and parallel streaming of instruction to the CPU
A method of achieving higher execution speed at same clock speed
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems With pipelining, same number of instructions executes in less time. F D E F D E F D E F D E F D E F D E

Types of CPUs
CISC
Complex Instruction Set
Introduced in 1960s
Memory referencing operations
100s of assembly instructions
Complex in design
Simple compilers
Targets code size
RISC
Reduced Instruction Set
Introduced in 1950s
Load/store architecture
Around 40 assembly instructions per CPU
Simple in design
Complex compilers
Targets performance

Processor
In addition to the CPU, it may have:
Cache memories
Memory management unit
Memory protection unit
System Bus

Cache Memories
System performance is lowered
due to slow bus and memory
regardless of the CPU speed.
Improved performance by using
a high speed memory to store
frequently accessed
instructions/data.
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Bus (66 MHz) Bus (66 MHz) CPU (400 MHz) Memory Device (10 MHz) CPU + Cache (400 MHz) Memory Device (10 MHz)

Read Operation with a Cache
Cache hit
A requested instruction/data is in cache
Cache performance is high when cache hit rate is high
Cache miss
A requested instruction/data is not in cache
Cache performance is low when cache miss rate is high
Line fill
Retrieving instruction/data from external memory to cache incase of cache miss
Cache retrieves a group of instructions/data

Write Operation with a Cache
Write through
A CPU writing to a certain address writes to both external memory and caches.
Write back
A CPU writing to a certain address writes to caches only and postpones writing to external memories to a later time.

Memory Management Unit
AKA MMU
It is used for address translation from virtual address to physical address.
It provides memory protection functions as well.
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems VA PA CPU Memory Device MMU

System Bus
Connects the processor to the external memories.
There are 2 famous bus architectures:
Von-Neumann
Harvard
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems CPU Instruction/Data Memories CPU Instruction Memory Data Memory

System on Chip
Due to advancements in silicon technologies, it is possible to add more functionalities to the processor on chip.
A processor tends to be a complete system on chip.
In addition to the processor, it may have:
Co-processors
Memories
Direct Memory Access
Internal IO devices
IO controllers
Interrupt controller
Peripherals Bus

Co-Processor
A processor that supplements the functions of the primary processor.
Extensions include:
Floating point operations
Graphics
Digital signal processors
Encryption processors

Memories
They are used to store instructions and data.
They can be divided into:
Volatile memory
When power is off, contents are lost.
Non-volatile memory
When power is off, consents are preserved.

Volatile Memories Versus Non-Volatile Memories Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems

Direct Memory Access
A coprocessor that allows data transfers without the interference of the processor.
A key player in for HW concurrency.
It can move data between:
Memories
A memory and IO device
The speed is limited by the speed of the slowest device in the transfer.
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems CPU DMA Memory IO Device

IO Devices
They exchange information with the processor.
They include digital and non-digital signals.
Only digital signals are interfaced directly to the CPU.
Not all IO devices can be integrated on the chip.

Internal IO Devices
They can be integrated on chip because they
Are physically silicon devices
Have small size
Examples include:
Memories
ADCs
RTCs
IO controllers

External IO Devices
Devices can’t be integrated on chip because they:
Are physically non silicon devices
Have large size that is not easily integrated on chip
Have a bus interface that is different from that is used internally
Examples include:
LCD
Keypad
Speakers
Mic

IO Controllers
They are used to interface the off-chip IO devices to the chip.
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems CPU Signals Device Signals CPU IO Device IO Control

IO Address Allocation
This is necessary to control the IO devices.
There are 2 types:
IO mapped IO
Exclusive address space for the IO devices
Widely used in PC world
Memory mapped IO
IO devices and memories share same address space
Widely used in embedded systems

Memory Mapped IOs versus IO Mapped IOs
IO Mapped
x86…
Exclusive IO region
Different instructions to access IO
Processor has a single pin that separates the IO from memory.
Memory Mapped
ARM, PPC, MIPS, x86..
A memory region
Same instruction to access memory and IO
External address decoder decodes the address and decides whether to select a memory or a device.
IO region must be non-cacheable and all IO variables must be declared as volatile.

IO Management
Polling
A program continuously checks the IO device
Interrupt
If an IO device needs processor attention, it interrupts the processor.
A key player for multi-tasking and real-time
DMA

Interrupt Controller
Extends interrupt signals of the processors
Offloads the CPU by doing some of interrupt processing
Extra level of interrupt control
Maps the interrupt signal to the processor interrupt signal
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems CPU IO Device Interrupt Control

Interrupt Processing Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Interrupt Control

On Chip Bus
Connects the components of the SoC

Types of the SoC
Application specific integrated circuit (ASIC)
Programmable HW
FGPAs
CPLDs
Application specific instruction set processors (ASIPs)
DSPs
Media processors

Implementation Tradeoff Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems

Embedded Boards
PCBs that can be used to run an embedded SW on top of it.
It has:
SoC’s
Memories
IOs
A development board can be an evaluation board or a solution board.

Embedded Boards cont’d
Evaluation boards
Boards that has a controller and all possible IOs that the controller can connect to.
Used by controller manufacturers to test their own chip.
Design houses use them to develop their products’ prototypes.
Solutions boards
Used in actual product
Subset or a tuned version of the evaluation board

Exercise 2: Identify Your Embedded System Hardware
Goal: Identify embedded systems hardware
Identify the embedded hardware for the example in exercise 1
Time: 15 minutes

Course Outline
Introduction
Embedded Hardware
Embedded Software

Program
A SW that the hardware understands and runs to achieve a specific result.
A program is written in 1 or more programming languages.
A program may compose or can be a mix of:
Application
Middleware
Operating system
Device Driver
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems Device Drivers Operating Systems Middleware Application

Programming Languages in Embedded Systems
They can be:
Low level
Assembly
Machine code
High level
C/C++
Java
Ada

Machine Code and Assembly Programming
Machine code is
1’s and 0’s only
Understood by processor only
Inconvenient to write a program with
Mnemonic code
Machine code converted to symbols understood by programmers
Assembly language mnemonic code + pseudo instructions to improve programs readability

Assembly Instructions
Instruction consists of mnemonic (opcode) and operands
Opcode is an action taken by a processor
Operands is the target the opcode should take an action for/on
ADD A, B, C
Opcode: ADD
Operands: A, B, and C
Symantec: register A = register B + register C

Pros and Cons of Assembly Language
Pros
Readable and understandable compared to machine code
Easier to debug and maintain compared to machine code
Cons
Knowledge of HW and processor internals is necessary
Processor specific
Limited capabilities

C/C++ Programming
Processor independent
Flexible
Easier to write
Assembly can be inlined in C/C++
Greater productivity

Bootloader
The first program that should run when the system starts.
Initial code written in assembly and then switches to C/C++.
Initializes the HW for proper SW operation and jumps to the first program to run on the system.

Device Drivers
Pieces of SW that interface directly to/abstracts the HW devices.
A device driver is divided into 2 layers:
Low level: HW dependent
High level: OS dependent
Device drivers are installed during bootloading or when a device is used for the 1 st time in the system or whenever the device is plugged.
Amr Ali Abdel-Naby@2011 Introduction to Embedded Systems HLD Operating Systems Middleware Application LLD

Operating System
A SW that manages HW and SW system resources.
It provide HW abstraction as well.
Windows and Unix can be used in embedded systems.
Another class of OSs called RTOS fits more in embedded systems.

Middleware
AKA libraries
Pieces of SW that solve a generic problem are gathered to form a middleware.
Examples:
GUI libraries
Video/Audio Decoders
USB stack
TCP/IP stacks

Application
Pieces of SW that:
Interface to the user
Tunes the middleware
Uses the OS and device drivers
To solve a specific problem

Embedded SW Application Form
There are several different types of SW architecture in use:
Endless loop
Cyclic execution
Interrupt controlled system
Cooperative multi-tasking
Preemptive multitasking

The Endless Loop
No tasks
Polled device I/O only
Often, performance too slow
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems DO FOREVER Request Input Device make a Measurement Wait for the Measurement to be ready Fetch the Value of the Measurement Process the Value of the Measurement IF Value is Reasonable THEN Prepare new Result using Value ELSE Result will be an Error Report Request Output Device deliver the Result Wait for the Result to be output Confirm that output is OK END DO

Basic Cyclic Executive
Endless loop of tasks
Tasks as independent as possible
Separate application issues.
Little interaction
Tasks share information easily.
Write/Read shared data
Time of complete loop determines real-time.
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems

Time-Driven Cyclic Executive
More precise timing
Timer interrupt determines real-time.
Sharing data OK
Polled device I/O only (except timer)

Multi-Rate Cyclic Executive
Some tasks need higher rate.
Integer multiple of base rate
Major cycle/Minor cycle(s)
Sharing data OK
Polled device I/O only (except timer)

Limitation of Cyclic Executives
Too low rate: Miss transient occurrences
Too high rate: Waste CPU power
Prefer interrupt-driven I/O
Timing of task executions imprecise
Data-dependent loops
SW maintenance nightmare

Caution Adding Interrupts
Interrupt service routine (ISR)
May need to pass data to task it is interrupting
Possible result: Inconsistent data
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems HW I/P Device ISR Shared Data Area SW using Data from ISR Old New

Multi-Rate Executive with Interrupts
ISRs write to one set of buffers.
Tasks use data from another set of buffers.
At each clock tick, data are copied.
Not a weekend “Garage” project
Sharing data among tasks, OK
Polled and interrupt-driven device I/O
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems HW I/P Device ISR Shared Data Area Task Data Buffers DI Copy data from ISR buffers to task buffers EI

Faster Response: Preemptive Scheduling
All previous schedulers: Non-Preemptive
Preemptive Scheduling == Task switches can take place at any point/time
Tasks can be switched in mid-execution.
Preemptive scheduler is very complex.
Polled and interrupt-driven device I/O are OK.
ISR data not delayed by a tick  Task can respond at once
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems Task 1 Task 2 Task 3 HW I/P Device ISR Task 3

Preemptive Scheduling Issues
Which task can preempt which task?
Answer is in priority.
Sharing data, Not OK
OS provide safe mechanism for passing data between ISRs/Tasks.
Amr Ali Abdel-Naby@ 2009 Real-Time Operating Systems Shared Data Area Task 1 Task 1 cont’d Task 2 with higher priority

An Intertask Communication Catalog
Data Transfer: Destructive reading, non-destructive writing
Message queues
Direct message passing
Indirect message passing
Mailboxes
Pipes
Data Transfer: Destructive writing, non-destructive reading
RTOS-protected globals: notepad registers, environment variables, …
Shared data area protected by a mutual exclusion mechanism.

An Intertask Communication Catalog cont’d
-ve synchronization == mutual exclusion
Semaphores
Mutexes
+ve synchronization
Event flags
Condition variables
Signals

Exercise 3: Identify Your Embedded System Software
Goal: Identify embedded systems hardware
Identify the embedded software for the example in exercise 1
Time: 15 minutes

Course Outline
Introduction
Embedded Hardware
Embedded Software

Depending on your business, you may need different set of tools.
Integrated Device Manufacturer (IDM)
Original Equipment Manufacturer (OEM)
Embedded SW design house
I will try to focus on the most commonly used tools.

Assembler
A SW program that converts source code written in assembly language into machine language.
Examples include:
GNU assembler

Compiler
A SW program that converts source code written in a high level programming language into another programming language.
C/C++  Assembly or Machine language
Compilation can be:
Native: Compiler and generated executables run on the same processor.
Cross: Compiler runs on a processor and the generated executables runs on a different processor.
Examples include:
ARMCC
GCC

Linker and Locator
A linker is a SW program that links the compilation and assemble operations’ outputs into a single executable.
A locator is a SW program that can change the memory map of the linker output.
It is common these days to see a combined linker-locator tool.
Examples include:
GCC

Simulator
A SW program that imitates a real thing, state of affairs, or processes.
Simulation is an approximation of the real time system.
A simulator is used when:
The real platform is not available.
It is dangerous to test on real system directly.
Examples include:
Proteus

Debugger
A SW program + HW device that interfaces my PC to my embedded HW.
It can be used to:
Set breakpoints
Dump memories
Trace execution
Watch variables
The HW can be
In circuit debugger
Debug agent SW on bard

Flash Loader
A SW program + HW device that interfaces my PC to my embedded HW.
It can be used to:
Erase ROM/Flash
Read ROM/Flash
Program ROM/Flash
Watch variables

Profiler
A SW program that gathers information about a program during execution.
Profiler is used to know which areas of code to optimize speed and memory.

Integrated Development Environment
A SW program that provides a comprehensive facilities for programmers.
It includes:
Assemblers
Compilers
Linkers
Debuggers
Simulators
Profilers
Text editors

Schematic Capture/Circuit Design Tool
A SW program that allows the circuit designer to enter his circuit design into CAD tools.
It is used for:
Design simulation
Design sketching
Examples include:
OrCAD
KiCAD

PCB Layout Design Tool
A SW program that allows the transformation of the circuit schematic capture into PCB layout that cab printed on a circuit board.

Oscilloscope
A HW Device that allows observation of constantly varying voltages.
It observes the exact wave shape across time.

Exercise 4: Identify Your Embedded System Development Tools
Goal: Identify embedded systems development tools
Identify the embedded system development tools for the example in exercise 1
Time: 15 minutes

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Introduction to embedded systems

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Introduction to embedded systems — Presentation Transcript