Table Of ContentRugged Embedded
Systems
Computing in Harsh
Environments
Augusto Vega
Pradip Bose
Alper Buyuktosunoglu
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Dedication
TomywifeChiaraandourlittleboyNiccolo`—theyteachmeeverydayhowtofind
happinessinthesimplestofthings.TotheamazinggroupofpeopleIhavethepriv-
ilege towork with at IBM.
AugustoVega
To all contributing members of the IBM-led project on: “Efficient resilience in
embedded computing,”sponsored byDARPAMTO under its PERFECT program.
Tomywife(Sharmila)andmymother(Reba)fortheirincredibleloveandsupport.
Pradip Bose
TomywifeAgnieszka,toourbabyboyJohnandtomyparents.Tothewonderful
group ofcolleagues that Iworkwith each day.
Alper Buyuktosunoglu
Contributors
J. Abella
Barcelona SupercomputingCenter,Barcelona,Spain
R.A. Ashraf
University ofCentral Florida, Orlando,FL,United States
P. Bose
IBM T. J. Watson Research Center,Yorktown Heights, NY, United States
A. Buyuktosunoglu
IBM T. J. Watson Research Center,Yorktown Heights, NY, United States
V.G. Castellana
Pacific NorthwestNationalLaboratory, Richland,WA, UnitedStates
F.J. Cazorla
IIIA-CSICand BarcelonaSupercomputing Center,Barcelona,Spain
M. Ceriani
PolytechnicUniversity of Milan, Milano, Italy
E.Cheng
StanfordUniversity, Stanford, CA,UnitedStates
R.F. DeMara
University ofCentral Florida, Orlando,FL,United States
F. Ferrandi
PolytechnicUniversity of Milan, Milano, Italy
R. Gioiosa
Pacific NorthwestNationalLaboratory, Richland,WA, UnitedStates
N. Imran
University ofCentral Florida, Orlando,FL,United States
M. Minutoli
Pacific NorthwestNationalLaboratory, Richland,WA, UnitedStates
S. Mitra
StanfordUniversity, Stanford, CA,UnitedStates
G. Palermo
PolytechnicUniversity of Milan, Milano, Italy
J. Rosenberg
Draper Laboratory, Cambridge, MA, UnitedStates
A. Tumeo
Pacific NorthwestNationalLaboratory, Richland,WA, UnitedStates
xiii
xiv Contributors
A. Vega
IBM T.J. WatsonResearchCenter,Yorktown Heights, NY, United States
R. Zalman
InfineonTechnologies,Neubiberg, Germany
X. Zhang
WashingtonUniversity, St. Louis,MO, United States
Preface
The adoption of rugged chips that can operate reliably even under extreme condi-
tions has experienced an unprecedented growth. This growth is in tune with the
revolutions related to mobile systems and the Internet of Things (IoT), emergence
of autonomous and semiautonomous transport systems (such as connected and
driverlesscars),andhighlyautomatedfactoriesandtheroboticsboom.Thenumbers
are astonishing—if we consider just a few domains (connected cars, wearable and
IoT devices, tablets and smartphones), we will end up having around 16 billion
embedded devices surrounding usby 2018, asFig. 1 shows.
Adistinctiveaspectofembeddedsystems(probablythemostinterestingone)is
thefactthattheyallowustotakecomputingvirtuallyanywhere,fromacar’sbraking
system to an interplanetary rover exploring another planet’s surface to a computer
attachedto(orevenimplantedinto!)ourbody.Inotherwords,thereexistsamobility
aspect—inherent to this type of systems—that gives rise to all sorts of design and
operation challenges, high energy efficiency and reliable operation being the most
criticalones.Inordertomeettargetenergybudgets,onecandecideto(1)minimize
error detection or error tolerance related overheads and/or (2) enable aggressive
power and energy management features, like low- or near-threshold voltage
Number of devices in use globally (in thousands)
20,000,000
18,000,000
16,000,000
Connected cars
14,000,000
Wearables
12,000,000
Connected TVs
10,000,000
8,000,000 Internet of thinks
6,000,000 Tablets
4,000,000
Smartphones
2,000,000
PCs
0
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014E2015E2016E2017E2018E
FIG.1
Embeddeddevicesgrowththrough2018.
Source:BusinessInsiderIntelligence.
xv
xvi Preface
operation. Unfortunately, both approaches have direct impact on error rates. The
hardening mechanisms (like hardened latches or error-correcting codes) may not
be affordable since they add extra complexity. Soft error rates (SERs) are known
toincreasesharplyasthesupplyvoltageisscaleddown.Itmayappeartobearather
challenging scenario. But looking back at the history of computers, we have over-
comesimilar(orevenlarger)challenges.Indeed,wehavealreadyhitseverepower
density-relatedissuesinthelate80susingbipolartransistorsandhereweare,almost
30 yearsafter, stillcreatingincreasingly powerfulcomputers and machines.
The challenges discussed above motivated us some years ago to ignite serious
discussion and brainstorming in the computer architecture community around the
mostcriticalaspectsofnew-generationharsh-environment-capableembedded pro-
cessors.Amongavarietyofactivities,wehavesuccessfullyorganizedthreeeditions
oftheworkshoponHighly-ReliablePower-EfficientEmbeddedDesigns(HARSH),
which have attracted the attention of researchers from academia, industry, and
governmentresearchlabsduringthelastyears.Someoftheexpertsthatcontributed
materialtothisbookhadpreviouslyparticipatedindifferenteditionsoftheHARSH
workshop. This book is in part the result of such continued efforts to foster the
discussioninthisdomaininvolvingsomeofthemostinfluentialexpertsinthearea
of ruggedembedded systems.
This book was also inspired by work that the guest editors have been pursuing
underDARPA’sPERFECT(PowerEfficiencyRevolutionforEmbeddedComputing
Technologies) program. The idea was to capture a representative sample of the
currentstateoftheartinthisfield,sothattheresearchchallenges,goals,andsolution
strategiesofthePERFECTprogramcanbeexaminedintherightperspective.Inthis
regard,thebookeditorswanttoacknowledgeDARPA’ssponsorshipundercontract
no.HR0011-13-C-0022.
We also express our deep gratitude to all the contributors for their valuable
timeandexceptionalwork.Needlesstosay,thisbookwouldnothavebeenpossible
withoutthem.Finally,wealsowanttoacknowledgethesupportreceivedfromthe
IBMT. J. Watson Research Center tomakethis book possible.
AugustoVega
Pradip Bose
AlperBuyuktosunoglu
Summer 2016
CHAPTER
1
Introduction
A. Vega, P. Bose, A.Buyuktosunoglu
IBMT.J.WatsonResearchCenter,YorktownHeights,NY,UnitedStates
Electronicdigitalcomputersareverypowerfultools.Theso-calleddigitalrevolution
hasbeenfueledmostlybychipsforwhichthenumberoftransistorsperunitareaon
integrated circuits kept doubling approximately every 18 months, following what
GordonMooreobservedin1975.Theresultingexponentialgrowthissoremarkable
thatitfundamentallychangedthewayweperceiveandinteractwithoursurrounding
world.Itisenoughtolookaroundtofindtracesofthisrevolutionalmosteverywhere.
Butthedramaticgrowthexhibitedbycomputersinthelastthreetofourdecadeshas
alsoreliedonafactthatgoesfrequentlyunnoticed:theyoperatedinquitepredictable
environmentsandwithplentifulresources.Twentyyearsago,forexample,adesktop
personalcomputersatonatableandworkedwithoutmuchconcernaboutpoweror
thermaldissipation;securitythreatsalsoconstitutedrareepisodes(computerswere
barelyconnectedifconnectedatall!);andthefewmobiledevicesavailabledidnot
havetoworrymuchaboutbatterylife.Atthattime,wehadtoputoureyesonsome
specificnichestolookfortrulysophisticatedsystems—i.e.,systemsthathadtooper-
ateonunfriendlyenvironmentsorundersignificantamountof“stress.”Oneofthose
nicheswas(andis)spaceexploration:forexample,NASA’sMarsPathfinderplan-
etary rover was equipped with a RAD6000 processor, a radiation-hardened
POWER1-based processor that was part of the rover’s on-board computer [1].
Releasedin1996,theRAD6000wasnotparticularlyimpressivebecauseofitscom-
putationalcapacity—itwasactuallyamodestprocessorcomparedtosomecontem-
poraryhigh-end(orevenembeddedsystem)microprocessors.Itscost—intheorder
ofseveralhundredthousanddollars—isbetterunderstoodasafunctionofthechip
ruggednesstowithstandtotalradiationdosesofmorethan1,000,000radsandtem-
peratures between (cid:1)25°Cand +105°Cinthe thin Martianatmosphere [2].
Inthelastdecade,computerscontinuedgrowingintermsofperformance(stillrid-
ing on Moore’s Law and the multicore era) and chip power consumption became
a critical concern. Since the early 2000s, processor design and manufacturing is
notdrivenbyjustperformanceanymorebutitisalsodeterminedbystrictpowerbud-
gets—aphenomenonusuallyreferredtoasthe“powerwall.”Therationalebehindthe
powerwallhasitsoriginsin1974,whenRobertDennardetal.fromtheIBMT.J.Watson
1
RuggedEmbeddedSystems.http://dx.doi.org/10.1016/B978-0-12-802459-1.00001-4
#2017ElsevierInc.Allrightsreserved.
2 CHAPTER 1 Introduction
ResearchCenter,postulatedthescalingrulesofmetal-oxide-semiconductorfield-effect
transistors(MOSFETs)[3].OnekeyassumptionoftheDennard’sscalingruleisthatoper-
atingvoltage(V)andcurrent(I)shouldscaleproportionallytothelineardimensionsofthe
transistorinordertokeeppowerconsumption(V(cid:3)I)proportionaltothetransistorarea
(A).Butmanufacturerswerenotabletoloweroperatingvoltagessufficientlyovertime
andpowerdensity(V(cid:3)I/A)keptgrowinguntilitreachedunsustainablelevels.Asaresult,
frequencyscalingwasknockeddownandindustryshiftedtomulticoredesignstocope
withsingle-threadperformancelimitations.
Thepowerwallhasfundamentallychangedthewaymodernprocessorsarecon-
ceived. Processors became aware of power consumption with additional on-chip
“intelligence” for powermanagement—clock gating anddynamic voltage and fre-
quency scaling (DVFS) are two popular dynamic power reduction techniques in
use today. But at the same time, chips turned out to be more susceptible to errors
(transient and permanent) as a consequence of thermal issues derived from high
power densities as well as low-voltage operation. In other words, we have hit
the reliability wall in addition to the power wall. The power and reliability walls
areinterlinkedasshowninFig.1.Thepowerwallforcesustowarddesignsthathave
tighter design margins and “better than worst case” design principles. But that
approach eventually degrades reliability (“mean time to failure”)—which in turn
requires redundancy and hardening techniques that increase power consumption
and forces usback against the powerwall. This isa vicious “karmic” cycle!
FIG.1
Relationshipandmutualeffectbetweenthepowerandreliabilitywalls.
Thisalreadyworryingoutlookexacerbatedintunewiththerevolutionsrelatedto
mobilesystemsandtheInternetofThings(IoT)sincetheaforementionedconstraints
(e.g., power consumption and battery life) get more strict and the challenges asso-
ciated with fault-tolerant and reliable operation become more critical. Embedded
computing has become pervasive and, as a result, many of the day-to-day devices
thatweuseandrelyonaresubjecttosimilarconstraints—insomecases,withcritical
consequences when they are not met. Automobiles are becoming “smarter” and in
