09 Sistemi Embedded

8/12/2019 09 Sistemi Embedded

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Giuseppe [email protected]

Pervasive Computing & Networking Lab. (PerLab)

Dept. of Information Engineering, University of Pisa

PerLab

Embedded Systems

A: A P, M D F

PerLab

Objectives

I

D

A E S

E S

PerLab

Overview

B C

M R

E S

E S


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PerLab

Definizione

S ,

, ,

I PC P .

I (, CD, , ).

PerLab

Aree di applicazione

A

C

S

R

I

U :D

D

M

T

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Solo alcuni esempi


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PerLab

Caratteristiche

S C

I I

S

P R

P O

PerLab

Specializzazione

U ( )L ,

F

.

PerLab

Hardware dedicato

I N , ,

.

I A


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PerLab

Applicazioni Real Time

U

S H . S I H

PerLab

Sistemi Embedded Distribuiti

C

V: L

S

R

S N

A

PerLab

Overview

B C

E S

E S


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PerLab

Principali requisiti

R

R

R

C

P

C

S !

PerLab

Requisiti funzionali

C D

(, , )

D (, , )

D

PerLab

Requisiti temporali

I

R

L L

I


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PerLab

Requisiti di affidabilit

AI (

) S (S)

G

C ( , )

R ()

DD = MTTF / (MTTF + MTTR)

PerLab

Consumo

I I

, ,

E

I M ( )

M ( )

I (. )

PerLab

Prestazioni

M

L


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PerLab

Costo

P .

,S (, , )

H ( CPU, , I/O)

S ( )

L HW SW (, , , )

N

PerLab

Overview

B C

M R

()

E S

PerLab

Features of Real-Time Kernels

M

R

R R

F PC


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PerLab

Virtual Memory and Address Translation

PerLab

Virtual Memory in Real-Time Systems

A :

(1) R

(2) R

(3) I

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Address Translation


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Implementing Real-Time Systems

I , :

(1) P,

(2) P

(3) L

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Minimizing Latency

.

PerLab

Interrupt Latency

P CPU


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Dispatch Latency

A

PerLab

Real-Time CPU Scheduling

P CPU ()

PerLab

Real-Time CPU Scheduling

P1: p=50 ms, t=20 ms t/p=0.4

P2: p=100 ms t=35 ms t/p=0.35

Scheduling of tasks when P2 has a higher priority

than P1


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PerLab

Rate Monotonic Scheduling

A

S = ; L =

P1 P2.

PerLab

Missed Deadlines with Rate Monotonic Scheduling

P1: p=50 ms, t=25 ms t/p=0.50

P2: p=80 ms t=35 ms t/p=0.44

Rate Monotonic Scheduling

Maximum utilization: 2(21/n-1) n=2: 0.83

PerLab

Earliest Deadline First Scheduling

P : , ;

,

P1: =50 , =25 /=0.50P2: =80 =35 /=0.44


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PerLab

Proportional Share Scheduling

A

T

PerLab

Overview

B C

M R

E S

PerLab

Distributed Embedded System

S

D

C WA, ,

WE , ,

W S N (N E S)


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PerLab

A

D ()

Wireless Sensor Networks

PerLab


PerLab


M C N


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PerLab

Sensor Node Architecture

Battery powered devices

Batteries cannot be changed nor recharged

Often negligible

power consumption

Local data processing

and data storage

Short range wireless communication

Radio is the most power hungrycomponent

PerLab

Sensors

S

S

(, , )

PerLab

Potential Application Areas

M A

E M

P A

H M I H

I

I


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PerLab

Military Applications

M ,

,

B

R

T

B

A , ,

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Environmental Monitoring

A

F

DB

PerLab


T ,

H M

G D I P

,


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PerLab


M

B

16

PerLab

Precision Agriculture

T

H

W S D

S

PerLab

R

H

( )

Health Applications


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PerLab

Home Applications

S H

( )

E

E E

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Commercial Applications

I C

V

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Industrial Applications

D I S S

F

P C

R D /

R

R


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PerLab

Industrial Applications

Low, K.S. Win, W.N.N. Er, M.J., Wireless Sensor Networks for Industrial Environments,Intl Conference on Computational Intelligence for Modelling, Control and Automation, 2005.

PerLab

Current snapshot

I

P

WSNs cannot be regarded any more

as an interesting research topic only

PerLab

Future perspectives

ON W I., W S N G M, A D, J2005 ://..//2.

P127 2010


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PerLab

Telos Mote

PerLab

The TinyOS operating system

S

,

TOS

(FIFO, )

( )

H

PerLab

TinyOS computation model

C

( )

( )

C

,

()

, Time


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PerLab

TinyOS development environment

C C

C OS

( )

TOS ( )

TOSSIM

(T), (TV)

PerLab

TinyViz

PerLab

Microserver-class Node: Stargate

E I

C : PA255 (32, 2.3 J/, 200 MH,1.5V),

C: B, 802.11 PC CF, M2 M

S: C , L 2.4


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PerLab

Applications of Stargate-class nodes

S

P

M

N

H

[NIMS, UCLA]

[Robotics, CMU]

[NESL, UCLA]

[CENS, UCLA] [Intel + UCLA]

PerLab

Networking Issues

PerLab

Features and Challenges

A

E T

S

T

ES ,

,

P


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PerLab

Features and Challenges

D

( , , )

Q S (QS),

S

D

( )

PerLab

IEEE 802.15.4/ZigBee standard

S P A N (PAN)

PH MAC

M

PAN

PerLab

IEEE 802.15.4 and ZigBee

IEEE 802.15.4 L, L, L P A N (PAN)

PH MAC

B S U L


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PerLab

IEEE 802.15.4 components

F F D (FFD)

PAN

R F D(RFD)

(PAN)

FFD

PerLab

IEEE 802.15.4/ZigBee Network Topologies

PerLab

IEEE 802.15.4: MAC protocol

D


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PerLab

IEEE 802.15.4: beacon enabled mode

PerLab

05/05/2010 74

At each trial the maximum

backoff-window size is

doubled

Only a limited number ofattempts is permitted

(macMaxCSMABackoffs)

CSMA/CA: Beacon-enabled mode

Transmission

No

Wait for a random

backoff time

Check channel status(CCA)

Idle?

Check channel status

(CCA)

Idle?No

Yes

Yes

PerLab

Acknowledgement Mechanism

O

D SACK

S R ACK ()

A

O (macMaxFrameRetries)


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PerLab

Single-hop Scenario

250 KB R

100 M S

% (/)

050%M L R

1 50S

PT G

C ON

1M B

15R

30CS

10D C N

2.4 GHPH

PerLab

802.15.4 MAC Unreliability Problem

0 5 10 15 20 25 30 35 40 45 500

10

20

30

40

50

60

70

80

90

100Delivery ratio

Poisson, Ack OFF,Power Man. OFF

Poisson, Ack OFF,Power Man. ON

Periodic, Ack OFF,Power Man. ON

Poisson, Ack ON,Power Man. OFF

Poisson, Ack ON,Power Man. ON

Periodic, Ack ON,Power Man. ON

Number of nodes

Deliveryratio(%)

PoissonTraffic,PowerManON

Periodic Traffic,

PowerManON

Poisson Traffic,PowerManOFF

G. Anastasi, M. Conti, M. Di Francesco, The MAC Unreliability Problem in IEEE 802.15.4 Sensor Networks,

ACM Conf. on Modeling, Analysis and Simulation of Wireless & Mobile Systems (MSWIM 2009), Oct. 2009.

PerLab

802.15.4 MAC Unreliability Problem

0 5 10 15 20 25 30 35 40 45 50

0

10

20

30

40

50

60

70

80

90

100Delivery ratio vs Packet Error Rate

P.E.R. 0%

P.E.R. 10%

P.E.R. 20%

P.E.R. 30%

P.E.R. 50%

Number of nodes

Deliveryratio(%)


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PerLab

Key Question

W 802.15.4 MACU P A?

PerLab

Causes and possible solutions

T MAC CSMA/CA

I MAC

T WSN

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CSMA/CA Parameter Values

Minimum Backoff

Window Exp.

07

D: 3

03

D: 3macMinBE

Maximum Backoff

Window Exp.

38

D: 5

5

()macMaxBE

Max number ofbackoff stages

05

D: 4

05

D: 4macMaxCSMABackoff

Max number of re-

transmissions

07

D: 3

3

(aMaxFrameRetries)macMaxFrameRetries

Notes2006 release2003 releaseParameter


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PerLab

Possible Solutions

( ) S

( ) S

( ): S

macMinBE macMaxBE macMaxCSMABackoff macMaxFrameRetries

DPS 3 5 4 3

SPS 7 8 5 7

NPS 8 10 10 10

PerLab

Performance

0 5 10 15 20 25 30 35 40 45 500

10

20

30

40

50

60

70

80

90

100

N

D(%)

D

DPS 1 /CP

SPS 1 /CP

NPS 1 /CP

DPS 10 /CP

SPS 10 /CP

NPS 10 /CP

0 5 10 15 2 0 2 5 30 35 40 4 5 5 00

0.05

0.1

0.15

0.2

0.25

N

M()

M L

DPS 1/CP

SPS 1/CP

NPS 1/CP

DPS 10/CP

SPS 10/CP

NPS 10/CP

0 5 10 15 2 0 2 5 30 35 40 4 5 5 00

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

N

P

(J/)

E

DPS 1/CP

SPS 1/CP

NPS 1/CP

DPS 10/CP

SPS 10/CP

NPS 10/CP

PerLab

A Final Question

A S R R?


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PerLab

Experimental Testbed

PerLab

Sensor Nodes

T STOS O S

IEEE 802.15.4 PH

IEEE TKN15.4 MAC (TUB)

P M E

P R A

PerLab

Simulation vs. Experiments (Default values)

RTx Enabled

RTx Disabled


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PerLab

Effects of clock misalignment

PerLab

Simulation vs. Experiments (SPS and NPS)

PerLab

The lesson learned

S IEEE 802.15.4 MAC

T

A

W MAC


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PerLab

Routing Protocols

PerLab

Taxonomy of routing schemes

F N

N

Q ( )

F, , SPIN, D D,

H C/T

S

LEACH, M,

L N

A/R R

GAF, SPAN,

PerLab

Flooding

E

I

H E

U WSN


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PerLab

LEACH

L E A CH

TDMA

W. R. Heinzelman, A. Chandrakasan, and H. Balakrishnan,

Energy-Efficient Communication Protocol for Wireless

MicrosensorNetworks , Proc. Hawaii International Conference

on System Sciences, January, 2000.

PerLab

MintRoute

T (TOS)

F

A. Woo, T. Tong, and D. Culler, Taming the underlying challenges of reliable multhop routing insensor networks, Proc. ACM SenSys 03, pp: 14-27, Los Angeles, CA, November 2003

PerLab

Questions?

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