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ADARTS

(Ada-based Design Approach for Real-Time Systems)

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ADARTS

The ADARTS method was created to developan Ada design from a Real-Time StructuredAnalysis (RTSA) specification.

Features of ADARTS are: principles for decomposing a real-time system into

concurrent tasks and information hiding modules.

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Task and module structuring criteria Applied to the leaf transformations on the RTSA data

flow/control flow diagrams. Each transformation isviewed from both a dynamic and static perspective.

Dynamic perspective: each transformation is considered as a separate thread of

control.

Static perspective: related functions (operations) identified in the RTSA are

grouped into a module based on the information hidingcriterion.

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ADARTS Steps and Work Products

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Steps in using ADARTS1. Develop an RTSA Specification

2. Structure the system into concurrent tasks

3. Structure the system into Information hiding modules

4. Integrate the task and module views

5. Develop an Ada-based design

6. Define component interface specifications

7. Develop the software incrementally

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Task Structuring A task (concurrent process) represents the execution

of a sequential program or, as in Ada, a sequentialcomponent in a concurrent program.

Each task deals with one sequential thread of execution; hence no concurrency is allowed within atask.

However overall system concurrency is obtained byhaving multiple tasks that execute in parallel.

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Task Structuring Categories I/O task structuring criteria

Internal Task Structuring criteria

Task Cohesion Criteria

Task Priority Criteria

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I/O task Structuring Criteria

Characteristics of I/O Devices

Characteristics of Data

Characteristics of passive devices

Polling frequency for passive devices

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Asynchronous Inputdevice

Generates an interrupt when it has producedsome input that requires processing by the

real-time system

Asynchronous Outputdevice

Generates an interrupt when it has finished processing output operation and is ready to

perform some new output.

Passive Input deviceInput from passive input device needs to beread either on polled basis or on demand

Passive Outputdevice

Output needs to be provided either on regular (periodic) basis or on demand

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Characteristics of Data

Discrete data Finite number of values

Continuous data (analog data) Infinite number of values Polling

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Characteristics of passive devices :Polling

Polling Sample the device on demand

Periodic polling

Data written to a data store

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Polling Frequency for Passive Device

Input device: how critical the input is and how frequently it is

expected to change.

Output device: How often data should be output in order to

prevent it from getting out of date.

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I/O TASK

AsynchronousI/O Task

Periodic I/OTask

Asynchronousdevice Passive device

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Asynchronous I/O Task or Aperiodic Task

Read Panel input Validate input

Handling ControlPanel Input

Processingcontrol

panel input

Panel

Inputs

Push buttons,

switch

Panel inputinterrupt

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Periodic Task

Readtemperature

input

Temperature

Temparature inputtask

Panel inputinterrupt

Temperature

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Resource monitor task

An input or output device that requests frommultiple sources have a resource monitor task to coordinate these request.

Ex.: printer monitor task

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Internal task structuring task Periodic task

Asynchronous task

Control task

User role task

Multiple task of same type

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TASK COHESION CRITERIA

Temporal cohesion

Sequential cohesion

Control cohesion

Functional cohesion

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Temporal cohesion

Certain functions may perform operations thatare activated by the same event.

functions may be grouped into a task, so that

they are executed each time the task receives astimulus

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Temporal cohesion : issues One function is more time critical than the

other.

Functions executed on separate processor

Sampling rate of functions

Functions with different priorities

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Sequential cohesion

Certain functions may perform operations thatmust be carried out sequentially.

The first function in the sequence is triggered by an asynchronous or periodic event. Thesesequentially dependent functions may becombined into one sequentially cohesive task.

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Sequential Cohesion : issues

Next transformation in the sequence alsoreceives inputs from another source andtherefore activated by receiving input from thatsource.

Next transformation is of lower priority andfollows time critical functions

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Control cohesion: issues State dependent transformations that are triggered by the

control transformations as a result of state transition. Group

State dependent transformations that are enabled or disabled by the control transformations as a result of state

transition. Separate task

State dependent transformations that are triggered by thecontrol transformations as a result of state transition andexecute for the duration of the state.

Non-state dependent transformations that sends events tothe control transformations, which cause it to change state.

group

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TASK PRIORITY CRITERIA Time critical:

A time critical function, i.e. one that needs to meeta hard deadline, needs to run at a high priority and

therefore be structured as a separate high prioritytask.

Computationally intensive A non-time critical computationally intensive

function (or set of functions) may run as a low priority task consuming spare CPU cycles

T k C i ti d

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Task Communication andSynchronization

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STATIC VIEW

Information Hiding And ModuleStructuring

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STATIC VIEW

Changing requirements are all too frequent andcannot be ignored.

Software design of designing maintainable and potentially reusable software componentsusing information hiding.

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Information Hiding And ModuleStructuring categories

Device interface modules

Behaviour hiding modules Data abstraction module State transition module Function driver module Algorithm hiding module

Software decision moudles

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Device interface modules (DIM)

Application software __________________

Virtual device interface(access procedures/functions)

____________________

Real world device interface __________________

real world I/O device

Software

Hardware

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DIM

Hides actual interface to the real-world device by providing a virtual interface to it.

For each I/O device and the functions on the DFD aremapped to the operations provided by DIM

ReadTemperature

inputTemperatureTemperature

sensorReadTemperature

FIG: DFDFIG: Temperature Sensor DIM

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h h d d l

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Behaviour hiding modulesData Abstraction Module

Read

Location

FIG: host aircraft position DAM

WriteLocation

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Behaviour hiding modulesState Transition Module

Processevent

Currentstate