i2cbus ,ethernet

7/26/2019 i2cbus ,Ethernet

1/39

2000 Overheads for

Networking for Embedded

Systems

Why we use networks.

Network abstractions.

Example networks.


2/39

2000 Overheads for

Network elements

PEPE

PE

network

communication link

distributed computing platform

PEs ma! be CP"s or #$%Cs&


3/39

2000 Overheads for

Networks in embedded

systems

PE

PE sensor

PE actuator

initial processing

more processing


4/39

2000 Overheads for

Why distributed?

Higher performance at lower cost.

Physically distributed activities---time

constants may not allow transmissionto central site.

mproved debugging---use one !P" in

network to debug others. #ay buy subsystems that have

embedded processors.


5/39

2000 Overheads for

Network abstractions

nternational $tandards %rgani&ation'$%( developed the %pen $ystems

nterconnection'%$( model todescribe networks)

*-layer model.

Provides a standard way to classifynetwork components and operations.


6/39

2000 Overheads for

OSI model

ph!sical mechanical' electrical

data link reliable data transport

network end(to(end service

transport connections

presentation data format

session application dialog control

application end(use interface


7/39

2000 Overheads for

OSI layers

Physical) connectors+ bit formats+ etc.

,ata link) error detection and control

across a single link 'single hop(. Network) end-to-end multi-hop data

communication.

ransport) provides connections mayoptimi&e network resources.


8/39

2000 Overheads for

OSI layers, contd.

$ession) services for end-userapplications) data grouping+

checkpointing+ etc. Presentation) data formats+

transformation services.

/pplication) interface betweennetwork and end-user programs.


9/39

2000 Overheads for

ardware architectures

#any di0erent types of networks)

topology

scheduling of communication routing.


10/39

2000 Overheads for

!oint"to"#oint networks

%ne source+ one or moredestinations+ no data switching

'serial port()

PE ) PE 2 PE *

link ) link 2


11/39

2000 Overheads for

$us networks

!ommon physical connection)

PE ) PE 2 PE * PE +

header address data ECC packet format


12/39

2000 Overheads for

$us arbitration

1ixed) $ame order of resolution everytime.

1air) every PE has same access overlong periods.

round-robin) rotate top priority among

Pes.

#','C #','C

fi-ed

round(robin

# , C # , C

# , C #, C


13/39

2000 Overheads for

%rossbar

in) in2 in* in+

out)

out2

out*

out+


14/39

2000 Overheads for

%rossbar characteristics

Non-blocking.

!an handle arbitrary multi-cast

combinations. $i&e proportional to n2.


15/39

2000 Overheads for

&ulti"stage networks

"se several stages of switchingelements.

%ften blocking. %ften smaller than crossbar.


16/39

2000 Overheads for

&essage"based

#rogramming

ransport layer provides message-based programming interface)

send_msg(adrs,data1);

,ata must be broken into packets atsource+ reassembled at destination.

,ata-push programming) make thingshappen in network based on datatransfers.


17/39

2000 Overheads for

I'% bus

,esigned for low-cost+ medium datarate applications.

!haracteristics) serial

multiple-master

3xed-priority arbitration. $everal microcontrollers come with

built-in 2! controllers.


18/39

2000 Overheads for

I'% #hysical layer

master ) master 2

slave ) slave 2

SCL

SDL data line

clock line


19/39

2000 Overheads for

I'% data format

$C.

$/.

&&&

M$,start

&&&

ack

&&&


20/39

2000 Overheads for

I'% electrical interface

$/.

%pen collector interface)

$C.


21/39

2000 Overheads for

I'% signaling

$ender pulls down bus for 4.

$ender listens to bus---if it tried to

send a 5 and heard a 4+ someoneelse is simultaneously transmitting.

ransmissions occur in 6-bit bytes.


22/39

2000 Overheads for

I'% data link layer

Every device has an address '* bitsin standard+ 54 bits in extension(.

7it 6 of address signals read or write. 8eneral call address allows

broadcast.


23/39

2000 Overheads for

I'% bus arbitration

$ender listens while sendingaddress.

When sender hears a con9ict+ if itsaddress is higher+ it stops signaling.

:ow-priority senders relin;uish

control early enough in clock cycle toallow bit to be transmitted reliably.


24/39

2000 Overheads for

I'% transmissions

multi(b!te write

read from slave

write' then read

$ adrs 0 data data P

$ adrs ) data P

$ adrs 0 data $ adrs ) data P


25/39

2000 Overheads for

&ulti#rocessor networks

#ultiple ,$Ps are often connected byhigh-speed networks for signal

processing)

/$P /$P

/$P /$P


26/39

2000 Overheads for

S()% link #orts

$ix per !P".

1our bits per link port.

Packets have


27/39

2000 Overheads for

Ethernet

,ominant non-telephone :/N.

>ersions) 54 #b?s+ 544 #b?s+ 5 8b?s

54 8b?s. 8oal) reliable communication over an

unreliable medium.


28/39

2000 Overheads for

Ethernet to#ology

7us-based system+ several possiblephysical layers)

# , C


29/39

2000 Overheads for

%S&(*%+

!arrier sense multiple access withcollision detection)

sense collisions exponentially back o0 in time

retransmit.


30/39

2000 Overheads for

E#onential back"off times

time


31/39

2000 Overheads for

Ethernet #acket format

preamblestart

frame

source

adrs

dest

adrs

data

pa!loadlength padding C1C


32/39

2000 Overheads for

Ethernet #erformance

@uality-of-service tends to non-linearly decrease at high load levels.

!anAt guarantee real-time deadlines.However+ may provide very goodservice at proper load levels.


33/39

2000 Overheads for

Internet !rotocol

nternet Protocol'P( is basis fornternet.

Provides an internetworkingstandard) between two Ethernets+Ethernet and token ring+ etc.

Higher-level services are built on topof P.


34/39

2000 Overheads for

I! in communication

ph!sical

data link

network

transport

presentation

application

session

ph!sical

data link

network

transport

presentation

application

session

ph!sical

data link

network

node # router node ,

%P


35/39


36/39

2000 Overheads for

I! addresses


37/39

2000 Overheads for

Internet routing

7est e0ort routing)

doesnAt guarantee data delivery at P

layer. Douting can vary)

session to session

packet to packet.


38/39

2000 Overheads for

igher"le-el Internet

ser-ices

ransmission !ontrol Protocol'!P(provides connection-oriented

service. @uality-of-service '@o$( guaranteed

services are under development.


39/39

2000 O h d f

he Internet ser-ice stack

%P

"/P

$MP

3CP"ser

/atagram

Protocol

43P 533P $M3P telnet

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