Technologies - Embedded System Design - Lecture Slides, Slides of Computer Science

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Outline

• Embedded systems overview

– What are they?

• Design challenge – optimizing design metrics

• Technologies

– Processor technologies

– IC technologies

– Design technologies

Embedded systems overview

• Computing systems are everywhere

• Most of us think of “desktop” computers

– PC’s

– Laptops

– Mainframes

– Servers

• But there’s another type of computing system

– Far more common...

A “short list” of embedded systems

And the list goes on and on

Anti-lock brakes Auto-focus cameras Automatic teller machines Automatic toll systems Automatic transmission Avionic systems Battery chargers Camcorders Cell phones Cell-phone base stations Cordless phones Cruise control Curbside check-in systems Digital cameras Disk drives Electronic card readers Electronic instruments Electronic toys/games Factory control Fax machines Fingerprint identifiers Home security systems Life-support systems Medical testing systems

Modems MPEG decoders Network cards Network switches/routers On-board navigation Pagers Photocopiers Point-of-sale systems Portable video games Printers Satellite phones Scanners Smart ovens/dishwashers Speech recognizers Stereo systems Teleconferencing systems Televisions Temperature controllers Theft tracking systems TV set-top boxes VCR’s, DVD players Video game consoles Video phones Washers and dryers

Some common characteristics of

embedded systems

• Single-functioned
  • Executes a single program, or has a custom hardware

for a single function.

• Tightly-constrained
  • Low cost, low power, small, fast, etc.
• Reactive and real-time
  • Continually reacts to changes in the system’s

environment

• Must compute certain results in real-time without

delay

Design challenge – optimizing design

metrics

• Obvious design goal:
  • Construct an implementation with desired

functionality

• Key design challenge:
  • Simultaneously optimize numerous design metrics
• Design metric
  • A measurable feature of a system’s

implementation

• Optimizing design metrics is a key challenge

Design challenge – optimizing

design metrics

• Common metrics

– Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost

– NRE cost (Non-Recurring Engineering cost): The one-time

monetary cost of designing the system

– Size: the physical space required by the system

– Performance: the execution time or throughput of the system

– Power: the amount of power consumed by the system

– Flexibility: the ability to change the functionality of the system without incurring heavy

NRE cost

Design metric competition --

improving one may worsen others

• Expertise with both software and

hardware is needed to optimize

design metrics

• Not just a hardware or software

expert, as is common

• A designer must be comfortable with

various technologies in order to

choose the best for a given

application and constraints

Performance Size

Power

NRE cost

Microcontroller

CCD preprocessor Pixel coprocessor A2D

D2A

JPEG codec

DMA controller

Memory controller ISA bus interface UART LCD ctrl

Display ctrl

Multiplier/Accum

Digital camera chip

lens

CCD

Hardware

Software

Time-to-market: a demanding

design metric

• Time required to develop a product

to the point it can be sold to

customers

• Market window
  • Period during which the product

would have highest sales

• Average time-to-market constraint is

about 8 months

• Delays can be costly

Revenues ($)

Time (months)

Losses due to delayed market entry

(cont.)

• Area = 1/2 * base * height
  • On-time = 1/2 * 2W * W
  • Delayed = 1/2 * (W-D+W)*(W-D)
• Percentage revenue loss = (D(3W-

D)/2W^2 )*100%

• Try some examples

On-time Delayed entry entry

Peak revenue

Peak revenue from

delayed entry

Market rise Market fall

W 2W

Time

D

On-time

Delayed

Revenues ($)

• Lifetime 2W=52 wks, delay D=4 wks
• (4(326 –4)/2*26^2) = 22%
• Lifetime 2W=52 wks, delay D=10 wks
• (10(326 –10)/2*26^2) = 50%
• Delays are costly!

NRE and unit cost metrics

• Costs:
  • Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost
  • NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system
  • total cost = NRE cost + unit cost * # of units
  • per-product cost = total cost / # of units

= (NRE cost / # of units) + unit cost

• Example

• NRE=$2000, unit=$
• For 10 units
  • total cost = $2000 + 10*$100 = $
  • per-product cost = $2000/10 + $100 = $

Amortizing NRE cost over the units results in an additional $200 per unit

The performance design metric

• Widely-used measure of system, widely-

abused

• Clock frequency, instructions per second – not good measures?
• Digital camera example – a user cares about how fast it processes images, not clock

speed or instructions per second

• Latency (response time)

• Time between task start and end
• e.g., Camera’s A and B process images in 0.25 seconds

• Throughput

• Tasks per second, e.g. Camera A processes 4 images per second
• Throughput can be more than latency seems to imply due to concurrency, e.g. Camera B

may process 8 images per second (by capturing a new image while previous image is

being stored).

• Speedup of B over A = B’s performance / A’s

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Three key embedded system

technologies

• Processor technology

• IC technology

• Design technology

Processor technology

• Processors vary in their customization for the problem at hand

total = 0

for i = 1 to N loop

total += M[i]

end loop

General-purpose

processor

Single-purpose

processor

Application-specific

processor

Desired

functionality

General-purpose processors

• Programmable device used in a variety of applications
  • Also known as “microprocessor”
• Features
  • Program memory
  • General datapath with large register file and general ALU
• User benefits
  • Low time-to-market and NRE costs
  • High flexibility
• “Pentium” the most well-known, but there are

hundreds of others

IR PC

Register file

General ALU

Controller Datapath

Program memory

Assembly code

for:

total = 0

for i =1 to …

Control logic and State register

Data memory