Tuesday, March 17, 2015 Sam Siewert

SE300

SWE Practices

Lecture 10 – Introduction to Event-

Driven Architectures

Copyright {c} 2014 by the McGraw-Hill Companies, Inc. All rights Reserved.

6-2

Four Common Types of Systems

(a) Interactive subsystem

a

b

c

c

z

y x

a

a/x

b/y c/z

b

(b) Event-driven subsystem

(c) Transformational subsystem (d) Database subsystem

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Minute Paper

Software Services – What Are They?

– Periodic Requests for Service

– Peer-to-Peer Requests vs. Client and Server?

– Describe Services and What Might Differentiate a Server from an

Event-Driven Service

– Concurrency?

Event-Driven Architectures Not All Event-Driven Systems are Embedded, But Many Are

Embedded Systems - Predictable Response, Hard Real-Time Integrated Services

Definition of Embedded System – Not Just “Small”, but Purposed – Provides Specific Services Rather than General Purpose Computing

– Often No Direct Connection to User Input/Output

– Contained within a Larger System as a Sub-system

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Many Real-Time Embedded Systems Real Time – Must Respond to Requests for Service by a Deadline relative to request

– Failure to Respond Prior to Deadline Results in a System Failure

– Request Rate for Service Driven by Real-World Events

– Controls Processes and Delivers Deadline Driven Services

Anti-Lock Braking

Streaming Media (Video and Audio)

Process Control

Aircraft Flight Control

Robotic Systems

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Why are RT Embedded Systems a Challenge?

– Real-Time Services – Correct Results on time – Deadlines!

Multi-service Concurrency Required, for Software, Multi-threaded

Management of CPU, IO, and Memory Resources

– CPU Resource

Modern architecture – high throughput, less deterministic

pipelines, super-scalar, branch prediction, VM, split-transaction and burst

transfer bus interfaces, multi-level caches

– I/O Interface Resources

Sensors / Actuators (Interaction with Real World) - Latency

Networks (Latency and QoS) - Lag

– Memory Hierarchy Resources

Register file, L1/L2 cache, SRAM, dynamic RAM, Flash

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How to Make RT Embedded Systems Easier!

RT Service and CPU Resource Management

– RT Theory, Practice, and Pitfalls (Theory -> System)

RMA Theory (Real-Time Systems Class)

Prediction and Measurement of Performance

When to Allocate Services/Functions to HW, FW, or SW

– Multi-threaded RTOS Systems

Design Methods (DFD, SDL, EFSM and UML methods)

RTOS Mechanisms (e.g. message queue, signal, semaphore)

Analysis Tools (e.g. Windview, KernelShark)

I/O Device Interfaces and Drivers – Abstracted SW-HW Interfaces

– Interaction with Memory System (MMIO, DMAs, Plug-n-Play)

Memory Hierarchy Analysis and Abstraction – Multi-level Cache Performance Models

– Abstracted Non-Volatile Memory Filesystems

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How to Make RT Embedded Systems Easier!

RT Service and CPU Resource Management

– RT Theory, Practice, and Pitfalls (Theory -> System)

RMA and DMA Resource Theory

Prediction and Measurement of Performance

When to Allocate Services/Functions to HW, FW, or SW

– Multi-threaded RTOS Systems

Design Methods (DFD, SDL, EFSM and MSC methods)

RTOS Mechanisms (e.g. message queue, signal, semaphore)

I/O Device Interfaces and Drivers – Abstracted SW-HW Interfaces

– Interaction with Memory System (MMIO, DMAs, Plug-n-Play)

Memory Hierarchy Analysis and Abstraction – Multi-level Cache Performance Models

– Abstracted Non-Volatile Memory Filesystems

Types of Event-Driver Systems

Periodic – Predictable Load, Polled or Max Interrupt

Rate Controlled

Sporadic – Upper Bound on Request Rate

Known/Limited

Aperiodic – Driver Completely by Interrupt Rate, No

Masking, All Events are Queued in a Backlog

Periodic Most Common – Sporadic/Aperiodic Typical of

Error Handling

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Example Event-Driven Application -

VOIP Voice / Internet Protocol

– 8 bit Mono

– 16 bit Mono

– 16 bit Stereo

QoS

– Transport

– Buffering

– Sequencing and Dropouts

Point-to-Point

– Simplex

– Duplex

Conference Call

– Audio Buffer Co-Adding

– Session Control Protocol

– Mute Feature

CU Student – Testing VOIP from “Chip Up”

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Example Projects – Video Conferencing

Combines VOIP and Video

QoS

– Frame Rate

– Frame Compression

– Transport

– Buffering

– Sequencing and Dropouts

CPU Intensive

Transport Intensive

Session Protocol

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Example Projects – Mobile Platforms

Camera Line Followers

– Image Processing

– Steering, Motor Control

– Collision Avoidance

– Tethered or Wireless

– Speed and Curvature

Rovers

– GPS (with compass)

– GPS + Optical Navigation

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Example Projects – Robotic Arm

5 DOF Robotic Arm

– Dead-Reckoning with Limits

Monitoring

– Full-feedback

Pick and Place Tasks

– Find Target and Grapple

Object

– Move to New Location and

Place

– Stack Blocks

Embedded Camera in

Grappler

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Example Projects – Tilt/Pan Video Tracking

Camera Peak-Up

– Camera tilts and pans to track object

Target Tracker

– fixed camera, laser pointer tilts and pans to track

Stereo Vision Tracker

Tracking Speed

Intensive Image Processing

Scanners

– Etch n Sketch

Scans Image

Redraws with Servos

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Brief Workbench / VxWorks Demo

Basic Host - Target IDE

– API Guide

– Programmer’s Guide

RTOS vs. OS

RTOS Facilitates Predictable Response

– Priority Preemptive, Run-to-completion Tasks

– Low Latency, Low Overhead ISRs

– Direct Translation of RMA (Rate Monotonic Analysis) into

Scheduling Priorities

OS Facilitates Fairness and Prevents Starvation

– Linux CFS – Completely Fair Scheduler

– Linux CFQ – Completely Fair Queue for I/O

– Different Objectives

Embedded Linux? Not All Event-Driven Systems are

HRT (Hard Real-Time) or Even Predictable Response

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CPU Scheduling Taxonomy –

Many Methods Execution Scheduling

Global-MP Local-Uniprocessor

Distributed Asymmetric

(AMP )

Symmetric

(SMP OS)

Preemptive Non-Preemptive

Fixed-Priority

Hybrid

Dynamic-Priority Cooperative

Batch

FCFS SJN

Co-Routine Continuation

Function

Heuristic EDF/LLF RR Timeslice

(desktop)

Multi-Frequency

Executives

Static Dynamic

Rate

Monotonic

Deadline

Monotonic

Dataflow

(Preemptive, Non-Preemptive Subtree

Under Each Global-MP Leaf)

SMT

(Micro-Paralell)

Most Often Used –

Round Robin SMP

(Linux, Windows, Mac OS-X)

Others, Less Often Used

Current Trends

Use of Linux for Interactive and Embedded

– Special Linux Kernel Builds and Patches (Compared to Server

Transaction Oriented)

– Use of POSIX Real-Time Extensions

– Best Effort to Predictable Response (not HRT)

RTOS – Proprietary (VxWorks), Open (FreeRTOS)

– Support for Rate Monotonic Analysis and Theory (Proofs)

– Tools for Event Analysis and Timing – Verification

– Embedded (Hidden)

Hybrid Architectures

– Hardware State-Machines Handle HRT

– Software is For Configuration, Interaction, and Management

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Next …

Activity Diagrams

– Concurrency

– Objects with Active Threads

(Tasks)

State-Machines

– Deterministic Response

– Model for a Task (Thread)

– Task Awaits and Activating

Event and Transitions to a New

Statet

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Next from Text …

SEPA (Pressman) – Chapter 14, 15 & 16

Goals for Software System Re-use and Maintenance

Legacy Systems

Refactoring

…

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