Embedded Systems Design: A Unified Hardware/Software IntroductionHardware/Software Introduction
Chapter 1: IntroductionChapter 1: Introduction
1
Outline
Embedded systems overviewy What are they?
Design challenge optimizing design metricsg g p g g Technologies
Processor technologies IC technologies Design technologies
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Embedded systems overviewy
Embedded computing systemsp g y Computing systems embedded within larger
products
Computers are in here...
and here...
Difficult to give a precise definition, though any computing system other than a desktop computer can be qualified as an embedded
and even here...
p qcomputing system
Lots more of these, though they cost a lot less each.
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Embedded systems overviewy
The trends of disappearing computerpp g p Laptops Personal Computers Mainframes Servers
But theres another type of computing system Far more common...
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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A short list of embedded systemsyAnti-lock brakesAuto-focus camerasAutomatic teller machines
ModemsMPEG decodersNetwork cards
Automatic toll systemsAutomatic transmissionAvionic systemsBattery chargersCamcordersCell phonesC ll h b t ti
Network switches/routersOn-board navigationPagersPhotocopiersPoint-of-sale systemsPortable video gamesP i tCell-phone base stations
Cordless phonesCruise controlCurbside check-in systemsDigital camerasDisk drivesElectronic card readers
PrintersSatellite phonesScannersSmart ovens/dishwashersSpeech recognizersStereo systemsTeleconferencing systemsElectronic card readers
Electronic instrumentsElectronic toys/gamesFactory controlFax machinesFingerprint identifiersHome security systems
Teleconferencing systemsTelevisionsTemperature controllersTheft tracking systemsTV set-top boxesVCRs, DVD playersVideo game consoles
And the list goes on and on
Life-support systemsMedical testing systems
Video phonesWashers and dryers
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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g
Some common characteristics of embedded systemssystems
Single-functionedg Executes a single program, repeatedly
Tightly-constrainedg y Low cost, low power, small, fast, etc.
Reactive and real-time Continually reacts to changes in the systems environment Some must compute certain results in real-time without delay
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An embedded system example -- a digital cameray p g
Digital camera chip
CCD preprocessor Pixel coprocessorA2D
D2A
g p
lens
CCD (Charge Coupled Device)
MicrocontrollerJPEG codec
DMA controller Display ctrl
Multiplier/Accum
Memory controller ISA bus interface UART LCD ctrl
Single-functioned as always is a digital camera, tightly-constrained to be low cost, low power, small, and fast, and to some extend is real-time
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small, and fast, and to some extend is real time
Design challenge optimizing design metricsg g p g g
Obvious design goal:g g Construct an implementation with desired functionality
Key design challenge:y g g Simultaneously optimize numerous design metrics
Design metric A measurable feature of a systems implementation Optimizing design metrics is a key challenge
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Design challenge optimizing design metricsg g p g g
Common metrics Unit cost: the monetary cost of manufacturing each copy of the system, excluding
NRE cost
NRE cost (Non Recurring Engineering cost): Th ti t t 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
Fl ibili Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Design challenge optimizing design metricsg g p g g
Common metrics (continued)( ) Time-to-prototype: the time needed to build a working version of the system Time-to-market: the time required to develop a system to the point that it can be
l d d ld released and sold to customers
Maintainability: the ability to modify the system after its initial release Correctness safety many moreCorrectness, safety, many more
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Design metric competition -- improving one may worsen othersworsen others
Expertise with both software Powerand hardware is needed to optimize design metrics
A designer must be comfortable with SizePerformance
gvarious technologies in order to choose the best for a given application and set of constraintsNRE cost
Software
Hardware
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Time-to-market: a demanding design metricg g
Time required to develop a product to the point it can be sold to customers
Market window Market window Period during which the product
would have highest sales
R
e
v
e
n
u
e
s
(
$
)
Average time-to-market constraint is about 8 months
Time (months)
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Losses due to delayed market entryy y
Simplified revenue model Product life = 2W, peak at W Time of market entry defines a
Peak revenue
Peak revenue from
(
$
) Time of market entry defines a triangle, representing market penetration
Triangle area equals revenue
delayed entry
Market rise Market fall
On-time
Delayed
R
e
v
e
n
u
e
s
(
Triangle area equals revenue Loss
The difference between the on-i d d l d i l
W 2WD
Delayed
time and delayed triangle areasOn-time Delayedentry entry
Time
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Losses due to delayed market entry (cont.)y y ( )
Area = 1/2 * base * heightArea 1/2 base height On-time = 1/2 * 2W * W Delayed = 1/2 * (W-D+W)*(W-D)
Peak revenue
Peak revenue from
(
$
)
Percentage revenue loss = (D(3W-D)/2W2)*100%
Try some examples
delayed entry
Market rise Market fall
On-time
Delayed
R
e
v
e
n
u
e
s
(
Try some examples
W 2WD
Delayed
Lifetime 2W=52 wks, delay D=4 wks (4*(3*26 4)/2*26^2) = 22%
Lifetime 2W=52 wks delay D=10 wksOn-time Delayedentry entry
Time Lifetime 2W=52 wks, delay D=10 wks (10*(3*26 10)/2*26^2) = 50% Delays are costly!
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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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 systemthe system Total cost : NRE cost plus the unit cost * # of units per-product cost = total cost / # of units
= (NRE cost / # of units) + unit cost( ) Example
NRE=$2000, unit=$100 For 10 units
total cost = $2000 + 10*$100 = $3000 per-product cost = $2000/10 + $100 = $300
Amortizing NRE cost over the units results in an dditi l $200 it
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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additional $200 per unit
NRE and unit cost metrics
Compare technologies by costs -- best depends on quantityp g y p q y Technology A: NRE=$2,000, unit=$100 Technology B: NRE=$30,000, unit=$30
Technology C: NRE=$100 000 unit=$2
$160,000
$200,000ABC
$160
$200ABC
0
0
)
o
s
t
Technology C: NRE=$100,000, unit=$2
$40,000
$80,000
$120,000
$40
$80
$120
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p
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$00 800 1600 2400
$00 800 1600 2400
Number of units (volume)Number of units (volume)
But must also consider time-to-marketEmbedded Systems Design: A Unified Hardware/Software
Introduction, (c) 2000 Vahid/Givargis16
But, must also consider time to market
The performance design metricp g
Widely-used (abused) measure of system performance 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 secondLatency (response time) Latency (response time)
Time between task start and end e.g., Cameras A and B process images in 0.25 seconds
Th h t Throughput Tasks per second, e.g. Camera A processes 4 images per second Throughput is not always the inverse of Latency due to concurrency, e.g. Camera B may
process 8 images per second (by capturing a new image while previous image is being process 8 images per second (by capturing a new image while previous image is being stored).
Speedup of B over A = Bs performance / As performance Throughput speedup = 8/4 = 2
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Throughput speedup 8/4 2
Three key embedded system technologiesy y g
Three key technologies for embedded systemsy g y Processor technology IC technology Design technology
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Processor technologygy
The architecture of the computation engine used to implement a t f ti litsystems functionality
Processor does not have to be programmable and does not generally mean a general-purpose processorg p p p
Application-specific Single-purpose (hardware)General-purpose (software)
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Processor technologygy
Processors vary in their customization for the problem at hand
total = 0for i = 1 to N loop
total += M[i]end loop
Desired functionality
General-purpose processor
Single-purpose processor
Application-specific processor
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General-purpose processorsp p p
Programmable devices also known as microprocessor (software) are used in a DatapathControllermicroprocessor (software) are used in a variety of applications
FeaturesRegister
file
p
Control logic and
State register
Program memory General datapath with large register file and
general ALUIR PC
GeneralALU
User benefits Low time-to-market and NRE costs High flexibility
Program memory
Assembly code for:
Datamemory
g ytotal = 0for i =1 to
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Single-purpose processorsg p p p
Digital circuit (hardware) designed to execute DatapathControllerexactly one program a.k.a. coprocessor, accelerator or peripheral
Features
DatapathController
Control logic
State
index
total Features
Contains only the components needed to execute a single programN
State register
Data
+
No program memory Benefits
Fast
memory
Low power Small size
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Application-specific processorspp p p
Programmable processor optimized for a DatapathControllerparticular class of applications having common characteristics Compromise between general-purpose and single-
Registers
Custom
Control logic and
State register
Compromise between general purpose and singlepurpose processors
FeaturesP
IR PCALU
Program memoryData
memory Program memory Optimized datapath Special functional units
Program memory
Assembly code for:
memory
Benefits Some flexibility, good performance, size and power
total = 0for i =1 to
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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IC technologygy
The manner in which a digital implementation (gate-level) is g p (g )mapped onto an Integrated Circuit (IC) ICs consist of numerous layers (perhaps 10 or more) and for
different IC technologies these layers are built at different stage
Integrated Circuit
source drainchanneloxidegate
Silicon substrate
IC package
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Silicon substrate
IC technologygy
Three types of IC technologiesyp g Full-custom/VLSI Semi-custom ASIC (gate array and standard cell) PLD (Programmable Logic Device)
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Full-custom/VLSI
All layers are optimized for a particular implementationy p p p Placing transistors Sizing transistors Routing wires
Benefits Excellent performance, small size, low power
Drawbacks High NRE cost (e.g., $300k), long time-to-market
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Semi-custom
Lower layers are fully or partially builty y p y Designers are left with routing of wires and maybe placing some
blocks Benefits
Good performance, good size, less NRE cost than a full-custom implementation (perhaps $10k to $100k)implementation (perhaps $10k to $100k)
DrawbacksStill require weeks to months to develop Still require weeks to months to develop
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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PLD (Programmable Logic Device)( g g )
All layers already existy y Designers can purchase an IC Connections on the IC are either created or destroyed to
implement desired functionality Field-Programmable Gate Array (FPGA) very popular
B fit Benefits Low NRE costs, almost instant IC availability
Drawbacks Drawbacks Bigger, expensive (perhaps $30 per unit), power hungry, slower
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Independence of processor and IC technologiesp p g
Basic tradeoff General vs. custom With respect to processor technology or IC technology The two technologies are independentThe two technologies are independent
General-purpose
processorASIP
Single-purpose
processorGeneral, Customized, processor processorproviding improved: providing improved:
Power efficiencyPerformance
Size
FlexibilityMaintainability
NRE cost
Semi-customPLD Full-custom
SizeCost (high volume)Time- to-prototype
Time-to-marketCost (low volume)
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Semi customPLD Full custom
The co-design ladderg
In the past: Sequential program code (e.g., C, VHDL) Hardware and software design
technologies were very different Recent maturation of synthesis Assembly instructions
Register transfers
Compilers(1960's,1970's)
Behavioral synthesis(1990's)
RT synthesisyenables a unified view of hardware and software
Hardware/software codesign
y
Machine instructions
Assemblers, linkers(1950's, 1960's)
RT synthesis(1980's, 1990's)
Logic synthesis(1970's, 1980's)
Logic equations / FSM's
Hardware/software codesign
Implementation
Machine instructions ( , )
Microprocessor plus program VLSI, ASIC, or PLD
Logic gates
bits: software implementation: hardware
The choice of hardware versus software for a particular function is simply a tradeoff among various design metrics, like performance, power, size, NRE cost, and especially flexibility; there is no fundamental difference
between what hardware or software can implement
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between what hardware or software can implement.
Moores law
The most important trend in embedded systems p y Predicted in 1965 by Intel co-founder Gordon MooreIC transistor capacity has doubled roughly every 18 months for
the past several decades10,000
1,000
10010
10 1
Logic transistors per chip
(in millions)
0.1
0.01
0.001
Note: logarithmic scale
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Graphical illustration of Moores lawp
1981 1984 1987 1990 1993 1996 1999 2002
10,000transistors
150,000,000transistors
Leading edgechip in 1981
Leading edgechip in 2002
Something that doubles frequently grows more quickly than most people realize!most people realize! A 2002 chip can hold about 15,000 1981 chips inside itself
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Design productivity increaseg p y
100,000
10,000
1,000
100
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Exponentially increased over the past few decades
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Design productivity gapg p y g p
While designer productivity has grown at an impressive rate over the past decades, the rate of improvement has not kept pace with chip capacity
10,000
1,000
10010
Logic transistors per chip
100,000
10,000
1000100 ProductivityGap10
10.1
0.01
chip(in millions)
100
101
0.1
y(K) Trans./Staff-Mo.IC capacity
productivity
0.001 0.01
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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Design productivity gapg p y g p
1981 leading edge chip required 100 designer months 10,000 transistors / 100 transistors/month
2002 leading edge chip requires 30,000 designer months 150,000,000 / 5000 transistors/month, ,
Designer cost increase from $1M to $300M10,000 100,0001,000
100101
0 1
Logic transistors per chip
(in millions)
10,0001000100101
Productivity(K) Trans./Staff-Mo.IC capacity
Gap
0.10.01
0.001
10.10.01
productivity
Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis
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The mythical man-monthy
The situation is even worse than the productivity gap indicates In theory, adding designers to team reduces project completion time In reality, productivity per designer decreases due to complexities of team management and
communication I th ft it k th thi l th (B k 1975) In the software community, known as the mythical man-month (Brooks 1975)
At some point, can actually lengthen project completion time! (Too many cooks)
60000 15Team
1M t i t 1 d i 5000 nt
h
)
2000030000400005000060000
2419
16 15 1618
23
Months until completion
1M transistors, 1 designer=5000 trans/month
Each additional designer reduces for 100 trans/month
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(
T
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s
.
/
m
o
10 20 30 400
1000020000 43
Individual
p
Number of designers
So 2 designers produce 4900 trans/month each
T
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m
P
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Number of designers
Summaryy
Embedded systems are everywhere Key challenge: optimization of design metrics
Design metrics compete with one anotherTh k t h l i Three key technologies Processor: general-purpose, application-specific, single-purpose IC: Full-custom, semi-custom, PLD Design: Compilation/synthesis, libraries/IP, test/verification
A unified view of hardware and software is necessary to improve productivityproductivity
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