Embedded Systems

1
Embedded Systems

• Introduction
• Chapter 1

2
Embedded Systems Design

• What is an Embedded System?
• Easiest answer is to compare them to a something
  that youre familiar with a PC

3
Tasks Performed

• PC
• A general purpose computer designed to perform an
  infinite number of tasks
• Can do many of these simultaneously
• If you can program it, a PC can perform it
• Software-centric system
• Easily reconfigured (reprogrammed) to perform
  various tasks

• Embedded System
• Designed to perform a specific task
• Does only one or a few thing(s)
• Task-centric system
• Hardware/Software system
• Changing the task generally means scrapping the
  entire system

4
Availability of Processors

• PC
• Built around a couple of architectures
• Intel
• Motorola
• Sun
• General purpose Complex Instruction Set Computer
  (CISC)
• Many special features
• Large instruction word

• Embedded System
• Hundreds of architectures available
• Quite often the developer will buy the design
  and build their own chips as part of their system
  
• FPGA
• ASIC
• Limited, Reduced Instruction Set Computer (RISC)
• Microcontroller
• Small instruction word

5
Cost

• PC
• The consumer/user is willing to pay for useful
  features
• Speed
• Memory
• Device support
• Cost is no object almost

• Embedded System
• Consumer/user only sees and pays for the end
  product
• Saving pennies per system can lead to millions of
  dollars in the developers pocket
• Consumer/user does not want to pay for the
  embedded processor

6
Timing Constraints

• PC
• Time is relative
• Pre-emptive system
• Sure Id like my job done now but if you have
  something more important to do then I can wait
• Non-Real-Time System

• Embedded System
• Time is of the essence
• Time-critical
• Task must complete in the allotted time or
  something really bad may happen
• Time-sensitive
• Now would be good but real soon is OK toobut not
  too long
• Real-Time System

7
Operating System

• PC
• Full featured OS
• Multi-tasking
• Pre-emptive scheduler
• File management
• Device management
• Basically 3 (now 2?)
• Windows
• Linux
• Mac OS

• Embedded System
• Minimal features
• Multi-tasking
• Priority based scheduling
• Interrupt driven
• If youre lucky and can afford it you can have a
  Real Time Operating System (RTOS)
• Various RTOSs available
• VxWorks (WindRiver)
• MicroC/OS (mucous)
• BREW (Qualcomm)
• Often there is no OS at all!

8
Implications of Failure

• PC
• Software failures, while annoying, are generally
  not catastrophic
• Thats why the reset button is on the front

• Embedded System
• Software failures may doom the entire system
• Think Mars rover
• The reset button is anything but conveniently
  placed
• Many systems must be designed to bring themselves
  back out of a coma

9
Power Usage

• PC
• In general, we dont ever think about it (except
  perhaps when we get our electricity bill)
• Power means heat
• Ever see the heat sink on a Pentium?
• We leave it turned on all the time

• Embedded System
• Batteries
• Get expensive
• Recharging can be inconvenient
• Thus, we worry about power consumption
• All features use power, including software
• Heat dissipation is often impossible
• System must sleep whenever possible to conserve
  power

10
Environmental Conditions

• PC
• Sits in the comfort of our office
• Harshest environmental issue is spilt coffee

• Embedded System
• Application specific
• Dust
• Smoke
• Heat
• Cold
• Humidity
• Altitude
• Gravity or lack thereof
• Vibration
• This is the stuff that can make embedded systems
  very expensive

11
Resources

• PC
• Multiple I/O devices
• Keyboard
• Mouse
• Monitor
• RW CD/DVD
• Speakers
• Printer
• Disc drives
• etc.
• Theres lots of stuff attached to the processor
  via various buses

• Embedded System
• A couple of buttons that handle multiple features
• Press once to set time
• Press twice to display month
• etc.
• Very few resources to manage
• Handled via a small number of I/O pins on the
  microcontroller

12
Code Space

• PC
• Programs reside on a disc until summoned into RAM
  by the OS
• Programs can be BIG
• Once there, the OS can swap them in and out as
  necessary
• Boots from ROM BIOS then hands off to disc-based
  OS
• Code can be changed at any time (with the
  exception of the boot ROM which is
  quasi-permanent)

• Embedded System
• There is no disc!
• Code resides in ROM and may even run from there
• RAM is generally limited and used for data
• Size is a limiting factor
• Interrupt based system (maybe)
• Boot code must initialize the system as well as
  perform POST (Power On Self Test) to ensure
  system integrity
• Code modification is difficult

13
Development Tools

• PC
• Rich set of tools
• Editors
• Compilers
• Debuggers
• Profilers
• Memory managers
• Device drivers
• etc.

• Embedded Systems
• Limited tools
• Often the microcontroller is selected based on
  available toolsets
• Since the system is primarily hardware, debugging
  is difficult
• ROM emulator acts as a hardware IDE of sorts
• Debugging circuitry is often built into the
  hardware
• Costs money in production but saves money in
  development/life cycle

14
Required Skills

• PC
• Software development
• Algorithm level programming
• Limited hardware understanding
• Underlying architecture (assembly language)

• Embedded Systems
• Software development
• Bit twiddling programming
• Extensive hardware understanding
• ASIC interfaces
• Communication protocols

15
Where To?

• Class will be in two parts (interleaved)
• theory utilizing the text book and other
  assigned readings
• practice utilizing the Parallax Basic Stamp
  development kits (which I will provide)

16
Next

• No class May 28, 2007 (Memorial Day)
• Read