Design of Sw for Embedded Systems

8/9/2019 Design of Sw for Embedded Systems

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Embedded Software Design

Peter R. Wihl(former Guest Lecturer)


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Oeriew

! Data flow "ractices (#hrough"ut)

! Real time s$stems

! Software design oeriew

! %ommunication "rotocols

! &n e'am"le software design

Feel free to ask questions at any time


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E'ecution low

! & diagram that describes the maor ste"s in these*uential software flow.

! +llustrates each logical ste" and decision "oint inthe oerall design of the software.

! Proides a starting "oint for the design of thesoftware.

! +s to embedded software as logical architecture isto hardware.

! +s ma""ed later to Routines, unctions or Obects


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-efore Designing E'ecution low

. +dentif$ which logical architecturalmodules are ma""ed to software.

/. +dentif$ what time "eriod all logicalsoftware function must be com"leted in.

0. +dentif$ an$ additional oerhead

functionalit$ due to modules ma""ed tosoftware and1or characteristics of the "h$sical design. ie. Polling1+nterru"ts


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Logical Design &rchitecture

E'am"le


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Ph$sical &rchitecture 2a""ing


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Logical Design &rchitecture

E'am"le


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Role of 2icrocontroller

! Read 34bit word from &D%

! %alculate Error %orrection %ode (/4bit)

! +nect "ossible error

! Detect if there is an error

! +f there is an error correct it! Write new 34bit word to D&%


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E'ecution low Diagram


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Data #hrough"ut in SW

! What is s$nchronous data flow5

6 Data arries at regular interals

! What is as$nchronous data flow5

6 Data does not arrie at regular interals

! What is isochronous data flow5

6 Data must be deliered within certain time

constraints


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Data low Practices

! Polling

! +nterru"t triggered (bloc7ing)

! +nterru"t triggered (non4bloc7ing)

! Eent drien

6 Often referred to as interru"t drien


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Sam"le Problem

! 8eed to receie 3 b$tes into a buffer and

then "rocess the buffer

! -$tes arrie as$nchronousl$


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Polling Oeriew


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Polling

main

do forever

count = 0

while count < 16

while byte not ready

nop

get byte

buffer[count] = byte

incr count

process buffer


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+nterru"t (-loc7ing) Oeriew


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+nterru"t #riggered

(-loc7ing)interrupt rx_byte

disable interrupts

count = 0

while count < 16 get byte


incr count

process buffer

enable interrupts

return

main

enable interrupts

do forever

nop


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+nterru"t (8on4-loc7ing) Oeriew


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+nterru"t #riggered

(8on4bloc7ing)interrupt rx_byte

if count < 16

get byte

buffer[count] = byte incr count

else if count = 16

process buffer

count = 0

return

main

count = 0

enable interrupts

do forever nop


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Eent Drien Oeriew


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Eent Drien

interrupt rx_byte

if count < 16

get byte


return

main

count = 0

enable interrupts

do forever if count = 16

process buffer

count = 0


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Real #ime

! 9ard real time

– Absolute deterministic response to an

event

! Soft real time

– Average response to an event


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Embedded Software Practices

Peter R. Wihl

E%E 3: S"ring /;;:


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Oeriew

! Data flow "ractices

! Real time s$stems

! %ommunication "rotocols

! Software design oeriew

! &n e'am"le software design

Feel free to ask questions at any time


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Data low #$"es





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Data low #$"es


6 Data arries at regular interals


6 Data does not arrie at regular interals


6 Data must be deliered within certain time

constraints


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Data low Practices

! Polling

! +nterru"t triggered (bloc7ing)

! +nterru"t triggered (non4bloc7ing)

! Eent drien

6 Often referred to as interru"t drien


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Sam"le Problem

! 8eed to receie 3 b$tes into a buffer and

then "rocess the buffer

! -$tes arrie as$nchronousl$


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Polling

main

do forever

count = 0

while count < 16

while byte not ready

nop

get byte


incr count

process buffer


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+nterru"t #riggered

(-loc7ing)interrupt rx_byte

disable interrupts

count = 0

while count < 16 get byte


incr count

process buffer

enable interrupts return

main

enable interrupts

do forever

nop


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+nterru"t #riggered

(8on4bloc7ing)interrupt rx_byte

if count < 16

get byte


else if count = 16

process buffer

count = 0

return

main

count = 0

enable interrupts

do forever nop


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Eent Drien

interrupt rx_byte

if count < 16

get byte


return

main

count = 0

enable interrupts

do forever if count = 16

process buffer

count = 0


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Real #ime

! 9ard real time

– Absolute deterministic response to an

event! Soft real time

– Average response to an event


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#ric7


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%ommunication Protocols

! What is a communication "rotocol5

6 &n established set of conentions b$ which

multi"le s$stems e'change data

! #he s"eech analog$

6 #he sounds $ou can ma7e are the

communication medium 6 #he language $ou use is the "rotocol


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Sam"le Protocol

Byte Data

; S$nchroni=ation

Pa$load si=e

/>/?si=e Pa$load

/?si=e? Pac7et chec7sum


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Protocol +nterru"t

interrupt rx_byte

get byte

checksum = byte ⊕ checksum

switch (state

!"#$ if byte = sync

checksum = byte

state = !%&'

!%&'

sie = byte

if sie ) 0 count = 0

state = *+",-+.

else

state = $/'$!2

*+",-+.


incr count

if count = sie state = $/'$!2

$/'$!2

if checksum = 0

state = +$$'*3

else

state = !"#$ +$$'*3

drop byte

return


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Protocol 2ain

main

state = !"#$

enable interrupts

do forever if state = +$$'*3

process buffer

state = !"#$

! #his is a sim"le eent

loo" that "roides

mutual e'clusion forthe buffer


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#ime or & -rea7


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Software Design Oeriew

! Re*uirements &nal$sis

! &rchitecture

! Design

! +m"lementation

! 2odule #esting

! Design @alidation #esting


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E'am"le Problem

! + want to build a 9eads A" Dis"la$ for m$

car.

! + would li7e to see both m$ engine RP2and fuel econom$ on m$ windshield.

! 2$ car has a serial diagnostic interface that

"roides this data.


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Re*uirements

! S$stem shall hae a 9eads A" Dis"la$

(9AD)

! S$stem shall interface with ehicleBsonboard diagnostic s$stem

! 9AD shall dis"la$ current RP2

! 9AD shall dis"la$ current fuel econom$

(2PG)


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9ardware %onstraints

! @ehicleBs onboard diagnostic s$stem

6 8eeds a wa7e4u" signal sent eer$ second

6 O"erates at ;,C;; b"s

! 9eads A" Dis"la$

6 /C3'/ "i'els

6 ull dis"la$ must be calculated and mirrored

6 O"erates at C,/;; b"s


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Processor Re*uirements

! Processor shall hae / A&R#s

. @ehicleBs onboard diagnostic s$stem

/. 9eads A" Dis"la$

! Processor shall hae a timer 6 @ehicleBs onboard diagnostic s$stem wa7e4u"

! Processor shall hae more than / b$tes of

memor$ 6 Processed dis"la$ image (:;3 b$tes)

6 2irrored dis"la$ image (:;3 b$tes)


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9ardware Design

Heads Up

Display

Vehicle

data

Processor /

microcontroller

Serial vehicle data

Serial display control


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Software &rchitecture

Heads Up

Display

Vehicle

dataSerial vehicle data


Vehicle data

interface

RP dataformatting

P! dataformatting

Display processing

RP data P! data

P! te"tRP te"t

Display control

interface

Display image


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Software Design

! 2odules

6 @ehicle Diagnostic +nterface (@D+)

6 RP2 Data ormatting (RD)

6 2PG Data ormatting (2PG)

6 Dis"la$ Processing (DP)

6 Dis"la$ %ontrol +nterface (D%+)


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Software Design

! 2odules

6 @ehicle Diagnostic +nterface (@D+)

6 RP2 Data ormatting (RD)

6 2PG Data ormatting (2PG)

6 Dis"la$ Processing (DP)

6 Dis"la$ %ontrol +nterface (D%+)

! 2ain1+nitiali=ation


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@ehicle Diagnostic +nterface

RP data P! data

Serial vehicle data Serial vehicle data

Receive bloc#Send $a#e up

signal%imer

Data type&

'"tract RP data '"tract P! data

RP P!

Data bloc#


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interrupt rx_byte

4

r5state = +$$'*3

4

return

extract_data

if data type = 7*2

e5tract 7*2 data

rpmformat(data

else if data type = 2*8 e5tract 2*8 data

mpgformat(data

return

main

4

do forever

4

if r5state = +$$'*3

e5tractdata

r5state = !"#$

4


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interrupt timer

wakeup = 1

return

tx_wakeup

send wakeup control

block

return

main

…

do forever

4 if wakeup = 1

t5wakeup

wakeup = 0

4


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2PG Data ormatting

P! integer data

%e"t formatting

)nteger to floating

point conversion

(loating point to

te"t conversion

%e"t P! value

(ormatted P! te"t

(loating point P! value


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Dis"la$ Processing(ormatted RP te"t (ormatted P! te"t

Display image

generation

irrored display image

irror image

RP placement P! placement

P! image

generation

RP image

generation

RP image P! image

Placed P!Placed RP

Display image


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Dis"la$ %ontrol +nterface

irrored display image


)mage to

command

conversion

*ommand send

Display command


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#est Plan

. #est functionalit$ of eer$ module

/. #est functionalit$ of eer$ module

interaction

0. #est functionalit$ of the final s$stem


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+m"lementation

#his is when $ou actuall$ write $our code.


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2odule #esting

! Sim"le im"lementations to test a single

module or module interaction

! #otal testing code will often be larger thanthe actual s$stemBs code base

! +s this good or bad5


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Design @erification #esting

! & scri"ted test "lan that guides a tester

through use of the s$stem

! & table with the followingF 6 Eer$ s$stem re*uirement

6 Whether or not the re*uirement was met

Documents

Design of Sw for Embedded Systems