This document provides an introduction to embedded computing and ARM processors. It discusses embedding computers in devices, characteristics of embedded applications, and why microprocessors are used. Challenges in embedded system design and performance are covered. The document introduces Unified Modeling Language (UML) for system design, including structural and behavioral description elements. It then provides an example specification for a model train controller system, covering requirements, components, message formatting, and class descriptions.

1. Introduction to
Embedded Computing and
ARM Processors
T.Ramprakash
AP/ECE
Ramco Institute of Technology
Academic Year 2016-17 (Odd Sem)

2. Complex Systems and Microprocessors
• Embedding Computers
• Characteristics of Embedded computing
application
• Why use microprocessors?
• Challenges in embedded computing system
design
• Performance of embedded computing systems

3. Embedding Computers
• It is any device that includes a programmable
computer but is not itself intended to be a
general purpose computer
• Whirlwind – 1940’s (aircraft simulator)
• Levels of Microprocessors based on their word
size
• Application of Microprocessors

4. BMW 850i Brake and Stability control system
• ASC +T (Automatic Stability control system)

5. Characteristics of Embedded computing application
• Complex Algorithms
• User Interface
• Realtime
• Multirate
• Manufacturing Cost
• Power and Energy

6. Why Use Microprocessors?
• Flexible
• Efficient
• Highly optimized
• Programmability
• Realtime
• Low power and low cost

7. Challenges in Embedded computing system design
• Hardware
• Deadlines
• Power Consumption
• Upgradeability

8. Performance of Embedded Computing Design
• CPU
• Platform
• Program
• Task
• Multiprocessor

9. FORMALISMS FOR SYSTEM DESIGN

10. FORMALISMS FOR SYSTEM DESIGN
• UML – Unified Modeling Language
• successive refinement and progressively adding
detail to the design
• Many graphical elements in UML diagram
• UML design emphasis on
– Design is described as number of interacting objects
rather than a few large monolithic blocks of code
– Objects will correspond to real pieces of S/W and H/W

11. FORMALISMS FOR SYSTEM DESIGN
• Structural Description
• Behavioral Description

12. Structural Description

13. An object in UML notation
d1: Display
pixels: array[] of pixels
elements
menu_items
object name
class name
attributes

14. A Class in UML notation
Display
pixels
elements
menu_items
mouse_click()
draw_box
operations
class name
Attributes

15. Relationships between objects and
classes
• Association: objects communicate but one
does not own the other.
• Aggregation: a complex object is made of
several smaller objects.
• Composition: aggregation in which owner
does not allow access to its components.
• Generalization: define one class in terms of
another.

16. Class derivation
– Derived class inherits attributes, operations of
base class.
Derived_class
Base_class
UML
generalization

17. Class derivation example
Display
pixels
elements
menu_items
pixel()
set_pixel()
mouse_click()
draw_box
BW_display Color_map_display
base
class
derived class

18. Multiple inheritance
Speaker Display
Multimedia_display
base classes
derived class

19. Behavioral Description

20. State Machine
a b
state state name
transition

21. Types of events
• Signal: asynchronous event.
• Call: synchronized communication.
• Timer: activated by time.

22. Signal event
<<signal>>
mouse_click
leftorright: button
x, y: position
declaration
a
b
mouse_click(x,y,button)
event description

23. Call event
c d
draw_box(10,5,3,2,blue)

24. Time out event
e f
tm(time-value)

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

26. Model Train Controller

27. Model Train setup
console
power
supply
rcvr motor
ECC address headercommand
Message

28. Requirements
• Console can control 8 trains on 1 track.
• Throttle has at least 63 levels.
• Inertia control adjusts responsiveness with at
least 8 levels.
• Emergency stop button.
• Error detection scheme on messages.

29. Requirement Form
name Model train controller
purpose Control speed of 8 model trains.
inputs Throttle, inertia, emergency stop,
train number
outputs Train control signals
functions Set engine speed. inertia; emergency
stop
performance Can update train speed at least 10
times/sec
manufacturing cost $50
power 10W (wall powered)
Size/Weight console comfortable for 2 hands

30. DCC
• Digital Command Control
• National Model Railroad Association
• Defines way in which model trains, controllers
communicate
• Standard S-9.1, DCC Electrical Standard.
• Standard S-9.2, DCC Communication Standard

31. DCC Electrical Standard
• Voltage moves around the power supply
voltage; adds no DC component.
time
logic 1 logic 0
58 ms >= 100 ms

32. DCC Communication Standard
• Basic packet format: PSA(sD)+E
• P: preamble = 1111111111.
• S: packet start bit = 0.
• A: Address data byte.
• s: data byte start bit.
• D: data byte (data payload).
• E: packet End bit = 1.

33. DCC Packet Types
• Baseline packet: minimum packet that must
be accepted by all DCC implementations.
– Address data byte gives receiver address.
– Instruction data byte gives basic instruction.
– Error correction data byte gives ECC

34. Specification
• Conceptual Specification
• Detailed Specification

35. Conceptual Specification
• Before we create a detailed specification, we
will make an initial, simplified specification.
command name parameters
set-speed speed
(positive/negative)
set-inertia inertia-value (non-
negative)
estop none

36. Message classes
command
set-inertia
value: unsigned-
integer
set-speed
value: integer
estop

37. Typical control sequence
:console :receiver
1..n: command

38. Console system classes
console
panel formatter transmitter
Knob* sender*
1
1
1
11
1
1
1
1
1

39. Console system classes
• Panel: describes analog knobs and interface
hardware.
• Formatter: turns knob settings into bit
streams.
• Transmitter: sends data on track.

40. Train system classes
train set
train
receiver controller
motor
interface
detector*
pulser*
1
1..t
1
1
1 1
1 1
1
1
1
1

41. Train class roles
• Receiver: digitizes signal from track.
• Controller: interprets received commands and
makes control decisions.
• Motor interface: generates signals required by
motor.

42. Detailed Specification
• Refining for more detailed specification
• Not complete specification, but will add detail
to the classes and major decisions in the
specification.

43. Console physical object classes
knobs*
train-knob: integer
speed-knob: integer
inertia-knob: unsigned-
integer
emergency-stop: boolean
Set-knobs()
pulser*
pulse-width: unsigned-integer
direction: boolean
sender*
send-bit()
detector*
read-bit() : integer

44. Train Speed Control
• Motor controlled by pulse width modulation:
V
+
-
duty
cycle

45. Panel and motor interface classes
panel
train-number() : integer
speed() : integer
inertia() : integer
estop() : boolean
new-settings()
motor-interface
speed: integer
panel class defines the controls.
new-settings() behavior reads the controls
motor-interface class defines the motor speed
held as state

46. Transmitter and receiver classes
transmitter
send-speed(adrs: integer,
speed: integer)
send-inertia(adrs: integer,
val: integer)
set-estop(adrs: integer)
receiver
current: command
new: boolean
read-cmd()
new-cmd() : boolean
rcv-type(msg-type:
command)
rcv-speed(val: integer)
rcv-inertia(val:integer)
Transmitter class has one behavior for each
type of message sent.
 Receiver function provides methods to
 Detect a new message;
 Determine its type;
 Read its parameters (estop has no
parameters).

47. Formatter class
formatter
current-train: integer
current-speed[ntrains]: integer
current-inertia[ntrains]:
unsigned-integer
current-estop[ntrains]: boolean
send-command()
panel-active() : boolean
operate()
 Formatter class holds state for each train, setting for current train.
 The operate() operation performs the basic formatting task.

48. Control input sequence diagramchangeinspeed/
inertia/estop
changein
trainnumber
:knobs :panel :formatter :transmitter
change in
control
settings
read panel
panel settings
panel-active
send-command
send-speed,
send-inertia.
send-estop
read panel
panel settings
read panel
panel settings
change in
train
number
set-knobs
new-settings

49. Formatter operate behavior
idle
update-panel()
send-command()
panel-active() new train number
other

50. Panel-active behavior
panel*:read-train()
current-train = train-knob
update-screen
changed = true
T
panel*:read-speed() current-speed = throttle
changed = true
T
F
...
F
...

51. Controller class
controller
current-train: integer
current-speed[ntrains]: integer
current-direction[ntrains]: boolean
current-inertia[ntrains]:
unsigned-integer
operate()
issue-command()

52. Controller operate behavior
issue-command()
receive-command()
wait for a
command
from receiver

53. Sequence diagram for set-speed
command
:receiver :controller :motor-interface :pulser*
new-cmd
cmd-type
rcv-speed set-speed set-pulse
set-pulse
set-pulse
set-pulse
set-pulse

54. Refined command classes
command
type: 3-bits
address: 3-bits
parity: 1-bit
set-inertia
type=001
value: 3-bits
set-speed
type=010
value: 7-bits
estop
type=000

55. Summary
• Separate specification and programming.
– Small mistakes are easier to fix in the spec.
– Big mistakes in programming cost a lot of time.
• You can’t completely separate specification
and architecture.
– Make a few tasteful assumptions.

56. Reference
• Wayne Wolf, “Computers as Components -
Principles of Embedded Computer System
Design”, Morgan Kaufmann, 2nd Edition,
2008.
• Marilyn Wolf, “Computers as Components -
Principles of Embedded Computing System
Design”, Third Edition “Morgan Kaufmann
Publisher,2012.