Embedded Systems: Principles and Practice

1
Embedded Systems Principles and Practice

• Christopher Alix
• Prairie City Computing, Inc.
• ECE 420
• April 9, 2007

2
Traditional Definition

• A dedicated computer (a combination of hardware
  and software) that serves a specific purpose, and
  which is completely encapsulated within another
  device.

3
Traditional Definition

• NOT general-purpose computers, which arent
  dedicated to a specific task.

• NOT devices which dont employ software at all
  (but which are becoming increasingly rare). Even
  something as simple as a digital clock is
  generally easier and cheaper to implement with a
  combination of hardware/software than as a
  hardware-only device.

4
Embedded Systems are Everywhere
5
Design Considerations
Common issues in many embedded system designs

• Form factor (size, shape, weight)
• Power (battery life, heat dissipation)
• Environment (shock, vibration, temperature,
  moisture, RF)

• Reliability
• User Interface
• Non-User Interface
• (or even )

6
Revised Definition

• Handheld appliances like cellular phone handsets,
  MP3 players, PDAs, calculators, game consoles,
  DVD players, etc. arent embedded in anything,
  but most engineers lump them in with ES because
  they share so many of the hardware and software
  constraints, components, tools, techniques and
  engineering skills relevant to traditional ES
  design.
• Given predictions that cellular handset sales
  will reach a billion units per year by 2009, the
  handheld device industry is essentially driving
  most of the innovation in the ES design world.

7
Software or Hardware? (Both!)

• Software for simple or high-reliability systems
  is often read-only firmware
• Most systems now use flash memory, enabling
  in-the-field software updates
• No externally-visible difference between hardware
  and software, so designers draw the line based
  on the specifics of the features to be
  implemented.

8
Software or Hardware? In Practice...

• Well-defined, fundamental, repetitive and/or
  performance-sensitive tasks are generally
  implemented in hardware.
• Complex, non-performance-sensitive, and/or
  likely-to-change tasks are generally implemented
  in software.

9
Hardware Architecture Processors

• Wide range of processor choices 4-, 8-, 16-,
  32-, even 64-bit Floating-point or integer math
• Specialized on-chip peripherals General Purpose
  Input/Output (GPIO) Comparators, amplifiers,
  LED drivers A/D and D/A conversion Digital
  Signal Processing Interfaces I2C, USB, and in
  between

10
Hardware Architecture FPGAs and CPLDs

• Field Programmable Gate Array
• Complex Programmable Logic Device
• Grab Bag of useful hardware on a single chip,
  often with flexible I/O
• Reconfigures itself on power-up
• Often used as a front end to reduce CPU
  processing demands or pin count

Xilinx (www.xilinx.com), Altera (www.altera.com)
11
Hardware Architecture FPGAs (continued)

• Powerful design tools generate FPGA code using
  software-like functional descriptions (VHDL,
  Verilog)
• Designs can be extensively simulated
• Programmable (FPGA) designs can be easily
  converted to hard coded ASIC (Application
  Specific Integrated Circuit) designs for lower
  cost at high volume

12
Hardware Architecture SoC

• System-on-a-Chip Use an FPGA/ASIC to implement
  the CPU, too
• Many standard CPU architectures are available as
  intellectual property--ready-to-use VHDL or
  Verilog code
• Core IP also available for complicated I/O
  tasks (IEEE1394, Ethernet, etc.)
• True single-chip solution for some systems

13
Software Architecture OS or No-OS?

• Very simple systems may run a single, main loop
  style program that does everything.
• Most systems have at least a low-level monitor
  program (like the BIOS in a PC) that handles
  power-on initialization and common
  hardware-related tasks.
• More complex systems may use an embedded OS like
  VxWorks or OS/9, or even an embedded variant of
  Linux or Windows.

14
Software Architecture Realtime

• Most embedded systems have tasks that must be
  performed reliably at a specific rate. (e.g.,
  capture a new audio sample every 22ms, or open a
  fuel injector within 10ms of a TDC indication).
• Embedded OSs and software use various techniques
  to satisfy this need for realtime performance.
• Realtime only means consistent--it doesnt mean
  fast. Many realtime systems are far slower
  than the average desktop PC, but you dont want
  your engine to die when you stick a CD in your CD
  player.

15
Development Process (Not ES-specific)

• Often done within the constraints of a
  structured design methodology as part of a Total
  Quality System (IEEE, ISO, 6s, etc.)
• Specification
• Design
• Development
• Verification against Design
• Validation against Specification

16
Specification

• Defining essential requirements of the final
  product, regardless of implementation
• Generally market-driven
• Look and feel and external interfaces
• Regulatory compliance requirements

17
Design

• Determining a specific solution that meets the
  overall project requirements
• Hardware and software considerations are closely
  related, so an understanding of both worlds is
  essential
• Multitude of constraints put a high price tag on
  overengineering

18
Design (System)

• Selection of hardware and software architectures
• Allocation of feature set between hardware and
  software
• Segmentation of system to enable parallel design
  (e.g., hardware, software, packaging)

19
Design (Hardware) Component Selection

• Low Volume Products (Cs, Ks) Minimum
  availability issues Some parts out of
  contention Can utilize distributor stock
  Parts finder services
• High Volume Products (Ms) Production
  limits/allocation Multiple sourcing
  requirements
• All Products Long-term availability and
  upgrade paths Regulatory changes (RoHS)

20
Design (Hardware) Circuit Design

• EDA (Electronic Design Automation) Tools
• Schematic capture (OrCAD, EAGLE, etc.)
• Circuit simulation where necessary (SPICE)
• Prototyping of new concepts
• Often incremental (borrowing circuits or portions
  of circuits from earlier products)
• Reference designs are a key resource
• Design-for-testability (DFT) and debugging tools

21
Design (Hardware) PCB Design

• Most non-trivial ES use high-density
  surface-mount components on multilayer PC boards
• 4-, 6-, 8-layer boards are common
• Dedicated power and ground layers simplify layout
  and improve RF characteristics
• More complicated than you might think!
• Surface-mount technology (SMT) offers high
  density and facilitates automated assemblybut
  are difficult or impossible to tweak later, so
  require extra care during the design process.

22
Design (Hardware) Physical Design

• Packaging
• RF shielding (radiation and susceptibility)
  Metallized enclosures Bonding of PCB to
  enclosure Connector shielding Shape and
  placement of openings
• Reliability shake and bake testing Drop
  testing

23
Design (Hardware) Regulatory Compliance

• US FCC (RF shielding), UL (safety) FDA,
  DOT, FAA, FRA, et al.
• International CSA (Canada), CE (Europe), GS,
  Europe CE mark
• Risk analysis (root-cause, fault-tree, etc.) is
  often required as a part of regulatory
  submissions
• Less innovative products are generally easier to
  gain regulatory approval for, for better or for
  worse.

24
Design (Software)

• Typically 101 (or higher) ratio of software
  engineers to hardware engineers on many ES
  projects
• Selection of development and debugging tools, in
  concert with hardware debugging support
• Software is key to debugging the hardware, and
  vice versa--groups must work closely together
• User interface design is important to the quality
  and usability of the resulting product

25
Development

• Hardware and software development is done in
  parallel, so agreement on standards and protocols
  is critical to keep the project moving forward
• Development often involves multiple groups and
  vendors, both in- and out-of-house
• A clear specification and design helps keep all
  the relevant parties moving in the same direction
• An extra hour of design time saves many hours of
  development time in virtually every case

26
Development (Hardware)

• PCB Fabrication and assembly generally outsourced
• High level of automation
• Most large-scale CM (Contract Manufacturing) is
  done overseas good communication is key to
  success
• Testability must be designed in (test coupons on
  PC boards, test jigs and fixtures, special
  provision for debugging very-high-speed signals,
  etc.)

27
Development (Software)

• Software makes the hardware work (or not work)
• Open-source tools common in ES world
• Debugging environments vary widely based on the
  capabilities of the hardware
• Software is easier to change than hardware, but
  quality is equally important

28
Verification

• Does the implementation match the design?
• Hardware and software test plans are essential
• Automated testing is valuable
• Regression testing is important as changes are
  made
• Good development processes offer traceability

29
Validation

• Does the product satisfy the requirements?
• If the design process was done right, validation
  should be a formality
• Product and Project Managers need to keep the
  fundamental requirements in mind during all
  phases of the project to ensure a positive
  outcome

30
Closing Comments

• Embedded Systems development is a large and
  growing part of both the EE and software worlds
• Managers and lead engineers in ES projects need a
  solid understanding of hardware and software
• Outsourcing is prevalent in every aspect of ES
  work
• Successful outcomes demand motivated, skilled and
  competent leaders with a broad set of skills

31
Embedded Systems Principles and Practice

• Christopher Alix
• Prairie City Computing, Inc.
• ECE 420
• April 9, 2007