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金仲达教授

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Pads LabChapter 1Embedded Computing金仲达教授清华大学资讯工程学系(Slides are taken from the textbook are embedded in embedded computing system designDesign design and Unified Modeling Language (UML)
Example: model train
Embedded system: any device that computer but is not computer.
Take advantage of application to optimize the design:
dont need all the bells and whistles.
digital assistant (PDA).
Printer.Cell phone.
Automobile: engine, brakes, dash, etc.
appliances.PC keyboard (scans keys).Early history
Late 1940s: MIT Whirlwind computer for real-time operations; Originally designed to control an aircraft simulator.
HP-35 calculator used several chips to in used engine controllers starting in 1970s.
Control fuelair mixture, engine timing, etc.
Multiple modes of operations: warm-up, hill climbing.
Provides lower emissions, better fuel efficiency.
Microprocessor varieties
includes IO devices, on-board memory.
Digital signal processor (DSP): microprocessor optimized for digital signal processing.
Application examples
Simple control: front panel of microwave oven, etc.
Canon EOS3has three
32-bit RISC CPU runs autofocus and eye control systems.
Analog TV: channel selection, etc.
Digital TV: programmable CPUs hardwired logic.
Automotive embedded automobile may have 100 mPs:4-bit checks seat belt;
run dashboard devices;
1632-bit microprocessor controls engine.
Anti-lock brake system (ABS): pumps brakes to reduce skidding.
Automatic stability control (ASCT): controls engine to improve stability.
ABS was introduced first> ASCT needs to interface to existing ABS module.
of embedded run sophisticated algo. or multiple algo.
Cell phone, laser printer.Often provide sophisticated user interfaces.
Real-time operation.Must finish operations by deadlines.
Hard real time: missing deadline causes failure.
Soft real time: missing deadline results in degraded performance.
Many systems are multi-rate: must handle operations at widely varying rates.
Low manufacturing cost.Many embedded systems are mass-market items that must have low manufacturing costs.
Limited memory, microprocessor power, etc.
Low power.Power is critical in power consumption increases system cost even in wall-powered devices.
Designed to tight deadlines by small teams.
6 month market window is common.
E.g, cant miss back-to-school window for calculator.
Why use
Alternatives: gate arrays (FPGAs), custom logic, etc.
Intuition: use much more logic to than does custom logic.
But, are often efficient, becausecan use same logic to perform different pipelinedlarge design VLSI simplify the design of families of products.
Although power logic isaclear winner for low power devices.
Modern offer features to help control power consumption.
Software design techniques can help reduce power consumption.
Challenges in embedded system designHow much hardware do we needHow big is the CPU MemoryHow do we meet our hardware or cleverer softwareHow do we minimize powerTurn off unnecessary logic reduce mem. accessesDoes it really workIs the specification correct Is the spec metHow do we test for real-time, real dataHow do we work on the development platformA procedure for
Understanding methodology helps you ensure you didnt skip anything.
Compilers, computer-aided design (CAD) tools, software engineering tools, etc, can be used to:help automate methodology steps;
keep track of the methodology itself.
Need to consider design speed, and user interface.
Manufacturing cost.Power requirements (physical size, etc.)Work with levels of design usesboth refinementAt each level of abstraction, we must:
analyze the design to determine of the current state of the design;
refine the design to add detail.
Level 1: language description of what the user wants and expects to get.
May be developed in several ways:talking directly to customers;talking to marketing ;
providing prototypes to users for comment.
Functional vs. non-functional asafunction of required to compute output;
size, weight, etc;power consumption;reliability;etc.Our requirements form
Example: GPS moving map map obtains position from GPS, paints map from local database.
Scotch RoadGPS moving map needs
Functionality: For automotive use. Show major roads and landmarks.
User interface: At least 400x600 pixel screen. Three buttons max. Pop-up menu.
Performance: Map scroll smoothly. Less than1sec power-up. Lock onto GPS within 15 sec
Physical sizeweight: Should fit in hand.
Power on4AA batteries.
GPS moving map requirements form
Level 2: SpecificationA more precise description of the system:should not architecture;
provides input to the architecture design process.
May include functional and non-functional elements.
May be executable or may be in mathematical form for proofs.
UML (Unified Modeling Language)GPS specification
Should include:What is received from GPS;map data;user interface;operations required to satisfy user requests;
background operations needed to keep the system running.
Level 3: Architecture designWhat major components go satisfying the specification
Hardware peripherals, etc.
Software programs and their operations.
Must take into account functional and non-functional
GPS moving map block moving map hardware moving map software
Level 4: HW and SW componentsMust spend time architecting the system before you start coding.
Some components are ready-made, some can be modified from existing designs, others must be designed from scratch.
Level 5: System integrationPut together the bugs appear only at this stage.
Haveaplan for integrating components to uncover bugs quickly, test as much functionality as early as possible.
System modelingNeed languages to describe systems:useful across several levels of abstraction;
understandable within and between organizations.
Block diagrams areastart, but dont cover everything.
(OO) of programming.
Object = state methods.State provides each object with its own identity.
Methods provide an abstract interface to the object.
Class: object typeDefines the objects state elements but state values may change over time.
Defines the methods used to interact with all objects of that type.
Each object has its own state.OO implementation in Cclass display {
pixels : pixeltype[IMAX,JMAX;
pixel(inti,int j)
void val, inti,int j) { pixels[i,j] = val; }}OO design principlesSome objects will closely correspond to real-world objects.
Some objects may be useful only for description or
Objects provide interfaces to readwrite state, hiding the objects implementation from the rest of the system.
UMLUnified Modeling by Booch et al.
;visual;useful at many levels of abstraction;
usable for all aspects of design.
UML object
d1: Display
pixels: array of is a2-D nameclass classThe operations provide the abstract interface between the classs implementation and other classes.
Operations may have arguments, return values.
An operation can examine andor modify the objects state.
between objects and classes
Association: objects communicate but one does not own the other.
object is made of several smaller objects.
Composition: aggregation in which owner does not allow access to its components.
define one class in terms of another.
Class one class in terms of another.
Derived class inherits attributes, operations of base class.
derivation classMultiple
Association: describes relationship between classes.
msg: ADPCM_stream
length : integermessage set
count : message nameLinks
Link: describes relationships between objects.
Example: Link defines the contains descriptionWe have discussed how to specify structureNow consider describing behavior of the viewexternal viewUse state state descriptions are written as event-driven state machines.
Machine changes state when receiving an input.
Events may come from inside or outside of the system
Signal: asynchronous event.
Call: synchronized communication.
Timer: activated by time.Types of events
Signal event:
leftorright: button
x, y: position description
Call event:
Timer state = = diagramShows sequence of operations over time.
Relates behaviors of multiple objects.
m: Mouse
u: train can control8trains on1track.
Throttle has at least 63 levels.
Inertia control adjusts responsiveness with at least8levels.
Emergency stop button.Error detection scheme on messages.
Requirements formConceptual we specification, we will make an initial, simplified specification.
Gives us practice in specification and UML.
Good idea in general to identify potential problems before investing too much effort in detail.
Can start with message definitions, which determines what the controller can doCommand speed (positive or inertial-value NoneMessage
value:
value:
1.n: command Major subsystem roles
Console:read state of front panel;format messages;transmit messages.
Train:receive message;interpret message;control the train.Console system
1 Console class roles
panel: describes analog knobs and interface hardware.
formatter: turns knob settings into bit streams.
transmitter: sends data on track.
Train system classestrain
1 Train class roles
receiver: digitizes signal from track.
controller: interprets received commands and makes control decisions.
motor interface: generates signals required by motor.
Detailed can now fill in the details of the conceptual classes; out the spec first helps us understand the basic relationships in the system.
Train speed controlMotor controlled by pulse width physical object classesknobs
train-knob: integer
speed-knob: integer
inertia-knob: unsigned-
boolean
pulse-width: unsigned-
direction:
read-bit : integerPanel and classespanel class defines the controls.
new-settings behavior reads the controls.
class defines the motor speed held as state.
train-number : integer
speed : integer
inertia : integer
estop :
speed: and receiver classes
for each type function provides methods to:detectanew message, decidetype, read parameters
integer,
speed: integer)
integer,
val: integer)
integer)
current: command
new:
new-cmd : boolean
rcv-speed(val: integer)
classFormatter class holds state for each train, setting for current train.
The operate operation performs the basic formatting task.
current-train: [ntrains: [[ntrains:
panel-active : input casesUseasoft panel to show current panel settings for each train.
Changing train number:
must change soft panel settings to reflect current trains speed, etc.
Controlling panel, check for changes, perform command.
Control input sequence in intrain panelpanel operate train behavior
= = trueT
= throttleF
. Controller [ntrains: the speedDont want to change speed
Controller should change speed gradually by sending several commands.
Sequence diagram for set-speed operate for afrom command classes
type: 3-bits
address: 3-bits
parity: 1-bit
value: 3-bits
value: computers are all around us.
Many have complex embedded HW and SWMany design challenges: design time, deadlines, power, etc.
Methodologies help manage design process.
design helps
UML system design language.
Provides structural and behavioral primitives.
Separate specification and programming.
Cant completely separate specification and architecture.
Makeafew tasteful assumptions.

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