DAC 2009 Applying Use Cases

8/6/2019 DAC 2009 Applying Use Cases

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Applying Use Cases toApplying Use Cases toMicrocontroller Code DevelopmentMicrocontroller Code Development

Chris GilbertChris Gilbert

Cypress SemiconductorCypress Semiconductor


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AgendaAgenda Why Use CasesWhy Use Cases

Microcontroller Project DevelopmentMicrocontroller Project Development Use Cases DefinedUse Cases Defined

Use Cases CompositionUse Cases Composition

General ExampleGeneral Example

Embedded ExampleEmbedded Example

ConclusionConclusion


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Why Use CasesWhy Use Cases Simple and extensible processSimple and extensible process

Provide a methodical approach to requirementsProvide a methodical approach to requirements

capture and definitioncapture and definition

Clarify system, subsystem, and componentClarify system, subsystem, and componentresponsibilitiesresponsibilities

Assist in decomposing the designAssist in decomposing the design

Identify special conditions or error handlingIdentify special conditions or error handling

Form the spring board from requirements toForm the spring board from requirements to

verificationverification

Applicable to objectApplicable to object --oriented and functionaloriented and functionaldevelopmentdevelopment


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Embedded Software DevelopmentLifecycleEmbedded Software DevelopmentLifecycle

RequirementsRequirements

Statement of w orkStatement of w ork Informal correspondence w ith the customerInformal correspondence w ith the customer

System descriptionSystem description

General and high levelGeneral and high level

Design is an informal process that maps theDesign is an informal process that maps therequirements to a frameworkrequirements to a framework

Functional ImplementationFunctional Implementation

VerificationVerification


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Embedded Software CodeEmbedded Software Code FrameworkFramework

Sequential flowSequential flow

RealReal --time operating system (RTOS)time operating system (RTOS) Interrupt drivenInterrupt driven State machineState machine Master/slaveMaster/slave

Functional ImplementationFunctional Implementation Small memory footprintSmall memory footprint Speed efficiency is often optimized due to relatively lowSpeed efficiency is often optimized due to relatively low

speed devicesspeed devices Limited development tool capabilityLimited development tool capability C or assembly languageC or assembly language


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Use Case HistoryUse Case History BackgroundBackground

IvarIvar Jacobson in 1985Jacobson in 1985

Introduced in the ObjectIntroduced in the Object--Oriented SoftwareOriented SoftwareEngineering (OOSE) ProcessEngineering (OOSE) Process

Primary element of the Unified SoftwarePrimary element of the Unified SoftwareDevelopment P rocessDevelopment P rocess

Supported in Universal Model Language (UML)Supported in Universal Model Language (UML)


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Use Case DefinitionUse Case DefinitionBoochBooch, Jacobson,, Jacobson, RumbaughRumbaugh ,, The UnifiedThe Unified

Software Development ProcessSoftware Development Process

Specifies a sequence of actions, includingSpecifies a sequence of actions, includingvariants, that the system can perform and thatvariants, that the system can perform and thatyields an observable result of value to anyields an observable result of value to an

actoractor


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What a Use Case IsntWhat a Use Case Isnt Description of the internal structure of theDescription of the internal structure of the

systemsystem

Data structuresData structures Data baseData base

Low level interfaceLow level interface

Single event or messageSingle event or message

Event or action internal to the system that isEvent or action internal to the system that isnot externally observable or does not producenot externally observable or does not produce

a result external to the systema result external to the system


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Use Case CompositionUse Case Composition NameName

Summarizes the usage of the system it modelsSummarizes the usage of the system it models

Description or Sequence of StepsDescription or Sequence of Steps Description of goal to be achievedDescription of goal to be achieved Describe the sequence of interactions between theDescribe the sequence of interactions between the

system and the actors that transpire from the inputsystem and the actors that transpire from the inputstimulus to the goalstimulus to the goal

ActorsActors Object outside the system that interact w ith the systemObject outside the system that interact w ith the system

AssumptionsAssumptions Assumptions, preconditions, and post condi tions requiredAssumptions, preconditions, and post condi tions required

for the use case to executefor the use case to execute


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Use Case DescriptionUse Case Description Brief descriptionBrief description

RelationshipsRelationships Relationship between the use case and actors or other useRelationship between the use case and actors or other use

casescases

Basic flowBasic flow

Describe the sequence of interactions between the systemDescribe the sequence of interactions between the systemand the actors that transpire from the input stimulus to theand the actors that transpire from the input stimulus to thegoalgoal

May include state charts, sequence diagrams, etc.May include state charts, sequence diagrams, etc.

Alternat ive flowAlternat ive flow

Special requirementsSpecial requirements QOS requirementsQOS requirements Requirements not naturally included in the flow descriptionRequirements not naturally included in the flow description


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ActorsActors DefinitionDefinition

Represents what interacts w ith the systemRepresents what interacts w ith the system Any object outside the system under developmentAny object outside the system under development

that has a significant interaction w ith the systemthat has a significant interaction w ith the system

CharacteristicsCharacteristics One or more per use caseOne or more per use case

Not necessarily involved in all use casesNot necessarily involved in all use cases ExamplesExamples

Users, other systems, subsystems, hardware orUsers, other systems, subsystems, hardware orsoftware components, etc.software components, etc.

Microcontroller peripherals such as A/ DMicrocontroller peripherals such as A/ Dconverter, serial interfaces, sensorsconverter, serial interfaces, sensors

Hardw are components, LCD, push buttons,Hardw are components, LCD, push buttons,sensorssensors


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Carbon MonoxideMonitor System

Test Button

Sounder

LED Display

CO Sensor

Carbon Monoxide Monitor Device

Microcontroller

Timers

Nonvolatile

Memory Calibration

Jumper

Actor ExampleActor Example


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Digital interface to the LED displayDigital interface to the LED display Display was defined as actorDisplay was defined as actor

A/ D converter internal to microcontrollerA/ D converter internal to microcontroller

Microcontroller interrupt controllerMicrocontroller interrupt controller

Not ActorsNot Actors


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Identifying Use CasesIdentifying Use Cases List the primary capabilities of the system,List the primary capabilities of the system,

then the actors, then identify specificthen the actors, then identify specific

scenarios w ithin each use case.scenarios w ithin each use case. Identify the actors to the system and theirIdentify the actors to the system and their

interactions, then group those into use cases.interactions, then group those into use cases.

Begin w ith a system scenario, identify theBegin w ith a system scenario, identify theactors, and combine those into use cases.actors, and combine those into use cases.


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Carbon Monoxide Monitor SystemCarbon Monoxide Monitor System

TimersTimers

CO SensorCO Sensor

LED DisplayLED Display

SounderSounder

Test ButtonTest Button NonvolatileNonvolatile

MemoryMemory

CalibrationCalibration

JumperJumper

Issue Alarm

Monitor COLevel

Report CO

Level

PerformUnit Test

1

1

Use Case DiagramUse Case Diagram

Calibrate

Unit


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Use Case: Monitor CO LevelUse Case: Monitor CO Level Brief DescriptionBrief Description

This use case is init iated periodically , measures the COThis use case is initiated periodically, measures the COsensor level, and computes the CO PPM value.sensor level, and computes the CO PPM value.

Basic FlowBasic Flow This use case is initiated every 30 seconds.This use case is initiated every 30 seconds.

The raw sensor voltage is measured.The raw sensor voltage is measured.

A PPM value is computed based on the measured value.A PPM value is computed based on the measured value.

The PPM value is averaged using a running average w ithThe PPM value is averaged using a running average w iththe last 3 readings.the last 3 readings.

RequirementsRequirements The PPM value is limited to values between 0 to 999The PPM value is limited to values between 0 to 999

inclusive.inclusive.


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Use Case: Perform Unit TestUse Case: Perform Unit Test Brief DescriptionBrief Description

Perform a self test of the unit and issue the alarm if anPerform a self test of the unit and issue the alarm if anabnormal test is encountered.abnormal test is encountered.

Basic FlowBasic Flow This use case is initiated w hen the test button is pressed.This use case is initiated w hen the test button is pressed. At a 2 second rate, the CO sensor is placed in test mode,At a 2 second rate, the CO sensor is placed in test mode,

and the sensor is measured by including the Monitor COand the sensor is measured by including the Monitor COLevel use case.Level use case.

Display the test CO level by including the Report CO LevelDisplay the test CO level by including the Report CO Level

use case.use case. If the CO level is w ithin the test alarm w indow, issue the COIf the CO level is w ithin the test alarm w indow, issue the CO

alarm by including the Issue Alarm use case.alarm by including the I ssue Alarm use case. If the CO level is outside the alarm threshold w indow, issueIf the CO level is outside the alarm threshold w indow, issue

the trouble alarm by including the Issue Alarm use case.the trouble alarm by including the Issue Alarm use case.

After 6 seconds of test, reset the unit if the CO alarm w asAfter 6 seconds of test, reset the unit if the CO alarm wasissued.issued.


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Use Case: Perform Unit TestUse Case: Perform Unit Test Alternate FlowAlternate Flow

I f the calibration jumper is present, reset theIf the calibration jumper is present, reset the

unit w ithout performing any unit tests.unit w ithout performing any unit tests. RequirementsRequirements

The test alarm w indow lower and upper boundsThe test alarm w indow lower and upper boundsare 200 and 400 PPM , respectively.are 200 and 400 PPM , respectively.


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SummarySummaryUse casesUse cases

Can be documented minimally, but effectivelyCan be documented minimally, but effectively

A complete use case model can be documented onA complete use case model can be documented onindex cardsindex cards

Suitable for customer reviewSuitable for customer review

Capture functional requirementsCapture functional requirements Drive the system architectureDrive the system architecture

Provide definition for designProvide definition for design

Are a starting place for verificationAre a starting place for verification Assist in identifying unusual or unexpectedAssist in identifying unusual or unexpected

aspects of the systemaspects of the system


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Questions andAnswersQuestions andAnswers

DAC 2009 Applying Use Cases

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