1. ACOE433 – Advanced Embedded Systems
Dr. Konstantinos Tatas

2. Introduction to Embedded Systems
Unit 1
Introduction to Embedded Systems

3. Microprocessors for Embedded systems
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...

4. Embedded systems overview
Embedded computing systems
Computing systems embedded within electronic devices
Hard to define. Nearly any computing system other than a desktop computer
Billions of units produced yearly, versus millions of desktop units
Perhaps 50 per household and per automobile
Computers are in here...
and here...
and even here...
Lots more of these, though they cost a lot less each.

5. A “short list” of embedded systems
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
And the list goes on and on

6. Definitions Broad definition: Narrow definition:
Any computer system that is not a general-purpose computer
That would include robots, and all portable devices
Narrow definition:
A computer system (software and hardware) that interacts with its physical environment, mainly without human intervention
That would exclude printers, modems, portable devices such as dvd and mp3 players, etc.

7. Some common characteristics of embedded systems
Single-functioned
Executes a single program, repeatedly
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

8. Considerations in embedded system design
An embedded system receives input from its environment through sensors, processes this input and acts upon its environment through actuators
Besides the usual software and hardware design issues the embedded system designer must consider the properties of the sensors and actuators and the environment itself
The ultimate test of an embedded systems are the laws of physics

9. An embedded system example – Digital camera
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
Single-functioned -- always a digital camera
Tightly-constrained -- Low cost, low power, small, fast
Reactive and real-time -- only to a small extent

10. 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

11. Design challenge – optimizing design metrics
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 released and sold to customers
Maintainability: the ability to modify the system after its initial release
Correctness, safety, many more

12. Design Economics (1)
The selling price of an IC Stotal=Ctotal/(1-m), Ctotal is manufacturing cost for a single IC, m desired profit margin
Costs for produce an IC
Non-recurring engineering costs (NREs)
Recurring engineering costs
Fixed costs

13. Design Economics (2) Non-recurring engineering costs (NREs)
Engineering design cost
Prototype manufacturing cost
Recurring costs
Process
Package
Test

14. 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=$100
For 10 units
total cost = $ *$100 = $3000
per-product cost = $2000/10 + $100 = $300
Amortizing NRE cost over the units results in an additional $200 per unit

15. NRE and unit cost metrics
Compare technologies by costs -- best depends on quantity
Technology A: NRE=$2,000, unit=$100
Technology B: NRE=$30,000, unit=$30
Technology C: NRE=$100,000, unit=$2
But, must also consider time-to-market

16. Summary Embedded systems are everywhere
Key challenge: optimization of design metrics
Design metrics compete with one another
A unified view of hardware and software is necessary to improve productivity
Three key technologies
Processor: general-purpose, application-specific, single- purpose
IC: Full-custom, semi-custom, PLD
Design: Compilation/synthesis, libraries/IP, test/verification

17. Embedded System Classification
Dr. Konstantinos Tatas

18. What is real-time? Is there any other kind?
A real-time computer system is a computer system where the correctness of the system behavior depends not only on the logical results of the computations, but also on the physical time when these results are produced.
By system behavior we mean the sequence of outputs in time of a system.

19. Real-time means reactive
A real-time computer system must react to stimuli from its environment
The instant when a result must be produced is called a deadline.
If a result has utility even after the deadline has passed, the deadline is classified as soft, otherwise it is firm.
If severe consequences could result if a firm deadline is missed, the deadline is called hard.
Example: Consider a traffic signal at a road before a railway crossing. If the traffic signal does not change to red before the train arrives, an accident could result.

20. Classification of Embedded Systems
Real-time vs NonReal-Time
Hard deadline
Failsafe
Fail-operational
Soft deadline
Firm deadline
Centralized vs Distributed

21. Fail-Safe hard-deadline RT systems
If a safe state can be identified and quickly reached upon the occurrence of a failure, then we call the system fail-safe.
Failsafeness is a characteristic of the controlled object, not the computer system.
In case a failure is detected in a railway signaling system, it is possible to set all signals to red and thus stop all the trains in order to bring the system to a safe state.
In failsafe applications the computer system must have a high error-detection coverage.
Often a watchdog, is required to monitor the operation of the computer system and put it in safe state.

22. Fail-Operational hard-deadline RT systems
In fail-operational applications, threre is no safe state
a flight control system aboard an airplane.
The computer system must remain operational and provide a minimal level of service even in the case of a failure to avoid a catastrophe

23. Guaranteed response systems
a design that operates correctly even in the case of a peak load and fault scenario is a system with a guaranteed response.
The probability of failure of a perfect system with guaranteed response is reduced to the probability that the assumptions about the peak load and the number and types of faults do not hold in reality.
This probability is called assumption coverage [Pow95].
Guaranteed response systems require careful planning and extensive analysis during the design phase.

24. Best-effort systems
If an analytic response guarantee cannot be given, we speak of a best-effort design.
Best-effort systems do not require a rigorous specification of the load- and fault-hypothesis.
The design proceeds according to best effort
the sufficiency of the design is established during the test and integration phases.
It is difficult to establish that a best-effort design operates correctly in a rare-event scenario.
Many non safety-critical real-time systems are designed as best-effort systems.

25. Embedded System Requirements and Specifications
Unit 2
Embedded System Requirements and Specifications

26. Embedded System Requirements
Essentially turning a concept into a product
Asking potential customers, understanding their needs
determining the best feature and price point
Sales and marketing usually responsible
R&D engineers should contribute

27. Embedded System Requirements
Functional: describe each function of the system
Input:
Output:
Processing:
Non-functional: system properties not related to its function
Power Consumption
Cost
Time-to-market
Reliability
Portability
Maintainability
Security

28. Requirements should be
Concise:
Brief yet complete and unambiguous
Structured:
Requirements should be numbered
Black-box view:
Not concerned with implementation
Verifiable:
Able to check if they are met by the implementation

29. Example: Digital Camera Requirements Draft
Functional:
R1. Image capture
Input: Light from lens
Output: Pixels corresponding to light at 10.2 Mpixels
R2. Image compression
Input: Pixels of uncompressed image
Output: Pixels of compressed image (compression ratio: 4:1)
R3. Image Display
Input: Pixels of compressed image
Output: Pixels of display on 4x3 inch LCD display
R3.1 Zoom Image display
Input: Pixels of compressed image, zoom area, zoom ratio
Output: Pixels of display at
R4. Image transfer
Output: USB stream of pixels of compressed image

30. Example: Digital Camera Requirements Draft
Non-Functional:
R5. Cost: 150€
R6. Weight: 800 g
R7. Power consumption (number of photographs away from mains)
R8. Security

31. UML diagrams (1/2)
Structural Modeling Diagrams Structure diagrams define the static architecture of a model. 
Package diagrams are used to divide the model into logical containers, or 'packages', and describe the interactions between them at a high level.
Class or Structural diagrams  define the basic building blocks of a model: the types, classes and general materials used to construct a full model.
Object diagrams show how instances of structural elements are related and used at run-time
Composite Structure diagrams provide a means of layering an element's structure and focusing on inner detail, construction and relationships
Component diagrams are used to model higher level or more complex structures, usually built up from one or more classes, and providing a well defined interface
Deployment diagrams show the physical disposition of significant artifacts within a real-world setting.

32. UML diagrams (2/2)
Behavioral Modeling Diagrams Behavior diagrams capture the varieties of interaction and instantaneous states within a model as it 'executes' over time
Use Case diagrams  are used to model user/system interactions. They define behavior, requirements and constraints in the form of scripts or scenarios.
Activity diagrams  have a wide number of uses, from defining basic program flow, to capturing the decision points and actions within any generalized process.
State Machine diagrams are essential to understanding the instant to instant condition, or "run state" of a model when it executes.
Communication diagrams show the network, and sequence, of messages or communications between objects at run-time, during a collaboration instance.
Sequence diagrams  are closely related to communication diagrams and show the sequence of messages passed between objects using a vertical timeline.
Timing diagrams fuse sequence and state diagrams to provide a view of an object's state over time, and messages which modify that state.
Interaction Overview diagrams fuse activity and sequence diagrams to allow interaction fragments to be easily combined with decision points and flows.

33. Sequence Diagram

34. State machines
transition a b
state
state name

35. Example state machine start finish input/output region found got menu
region = menu/
which_menu(i)
mouse_click(x,y,button)/
find_region(region)
call_menu(I)
region
found
got menu
item
called
menu item
region = drawing/
find_object(objid)
highlight(objid)
object
highlighted
found
object

36. Sequence diagram Shows sequence of operations over time.
Relates behaviors of multiple objects.

37. Sequence diagram example
m: Mouse
d1: Display
u: Menu
mouse_click(x,y,button)
which_menu(x,y,i)
time
call_menu(i)

38. Design example 1: Alarm Clock
Source: Wayne Wolf, “Computers as Components: Principles of Embedded Computing System Design”, Second edition, Morgan Kaufmann, 2008

39. Functional Requirements
Name: Alarm clock.
Purpose: A 24-h digital clock with a single alarm
Inputs: Six push buttons
set time
set alarm
Hour
minute
alarm on
alarm off.
Outputs:
Four-digit, clock-style output.
PM indicator light.
Alarm ready light.
Buzzer.
Functions Default mode: The display shows the current time. PM light is on from noon to midnight.
Hour and minute buttons are used to advance time and alarm, respectively. Pressing one of these buttons increments the hour/minute once.
Depress set time button: This button is held down while hour/minute buttons are pressed to set time. New time is automatically shown on display.
Depress set alarm button:While this button is held down, display shifts to current alarm setting; depressing hour/ minute buttons sets alarm value in a manner similar to setting time.
Alarm on: puts clock in alarm-on state, causes clock to turn on buzzer when current time reaches alarm time, turns on alarm ready light.
Alarm off: turns off buzzer, takes clock out of alarm-on state, turns off alarm ready light.

40. Non-functional Requirements
Performance: Displays hours and minutes but not seconds. Should be accurate within the accuracy of a typical microprocessor clock signal. (Excessive accuracy may unreasonably drive up the cost of generating an accurate clock.)
Manufacturing cost: Consumer product range. Cost will be dominated by the microprocessor system, not the buttons or display.
Power: Powered by AC through a standard power supply.
Physical size and weight: Small enough to fit on a nightstand with

41. Update time FSM
update-time is activated once per second and must update the seconds clock.
If it has counted 60 s, it must then update the displayed time;
when it does so, it must roll over between digits and keep track of AM-to- PM and PM-to-AM transitions.
It sends the updated time to the display object.
It also checks if the time has reached the alarm time to activate the buzzer

42. Unit 4 Embedded System Implementation Platforms

43. Implementation Platform
The hardware on which the embedded computing system will execute the software
Could be a combination of platforms
Hardware platforms:
General Purpose Processors
RISC
CISC
Application-Specific Processors
Microcontrollers
Digital Signal Processors
ASIPs
Hardware Accelerators
GPUs
FPGAs
Custom ICs

44. General-purpose processors
Datapath IR PC
Register
file
General
ALU
Controller
Program memory
Assembly code for:
total = 0
for i =1 to …
Control
logic and State register
Data
memory
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

45. Single-purpose processors
Datapath
Controller
Control logic
State register
Data
memory
index
total +
Digital circuit designed to execute exactly one program
a.k.a. coprocessor, accelerator or peripheral
Features
Contains only the components needed to execute a single program
No program memory
Benefits
Fast
Low power
Small size

46. Application-specific processors
Datapath IR PC
Registers
Custom
ALU
Controller
Program memory
Assembly code for:
total = 0
for i =1 to …
Control
logic and State register
Data
memory
Programmable processor optimized for a particular class of applications having common characteristics
Compromise between general-purpose and single-purpose processors
Features
Program memory
Optimized datapath
Special functional units
Benefits
Some flexibility, good performance, size and power

47. General Purpose Processors
High Flexibility
General Instruction Set
Good for all applications, optimized for none
Low development time
Programming in high-level language
Low/Medium Processing Power
Medium Cost
High Power Consumption

48. Application-Specific Processors: Microcontrollers
Medium Flexibility
ISA optimized for control applications
Low processing power
Not suitable for data intensive applications
Low power consumption
Low cost
Low development time

49. Application-Specific Processors: DSPs
Medium Flexibility
ISA optimized for optimized for fast execution of numerical algorithms necessary for analyzing signals
Medium/High processing power
Low/Medium power consumption
Medium cost
Low development time

50. Comparison of CMOS design methods/ Implementation Platforms
NRE
Unit Cost
Power Dissipation
Complexity of Implementation
Time-to-Market
Performance
Flexibility
μProcessor/DSP
low
medium
high
PLA
FPGA
Custom Design
Very high

51. Loop unrolling for (i=0; i<64; i++)
A technique for reducing the loop overhead
The overhead decreases as the unrolling factor increases at the expense of code size
Doesn’t work with zero overhead looping hardware DSPs
for (i=0; i<64; i++) {
sum +=*(data++); }
for (i=0; i<64/4; i++) {
sum +=*(data++); }

52. Loop Unrolling example
Unroll the following loop by a factor of 2, 4, and eight
for (i=0; i<64; i++) {
a[i] = b[i] + c[i+1]; }
ACOE343 - Embedded Real-Time Processor Systems - Frederick University

53. Loop Reordering Transformations
Change the relative order of execution of the iterations of a loop nest or nests.
Expose parallelism and improve memory locality.

54. Loop Reordering Transformations (1)
Loop Interchange
enable vectorization by interchanging an inner, dependent loop with an outer, independent loop;
improve vectorization by moving the independent loop with the largest range into the innermost position;
improve parallel performance by moving an independent loop outwards in a loop nest to increase the granularity of each iteration and reduce the number of barrier synchronizations;
reduce stride, ideally to stride 1; and
increase the number of loop- invariant expressions in the inner loop.

55. Loop Reordering Transformations (2)
Loop Reversal
Reversal changes the direction in which the loop traverses its iteration range.
It is often used in conjunction with other iteration space reordering transformations because it changes the dependence vectors