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Simula
torOperation
Advance
dTestbenching
SimulatorOperation
FileI/O,A
utomatedTesting
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Brie
fAsidePicoblaze
Interrupts
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In
terrupts
1ExternalInterruptSource.
Activehigh,
leveltrigge
red.
Interruptscan
beenabledanddisabledontheproce
ssor.Bydefaulton
power-up
Orreset,theinterruptsaredisabled(ignored)
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Inte
rruptFlow
Forcestheprocessortojumptoaddress
0xFFSavestheretur
naddress
Savesthez,cflags
Dis
ablesfurtherinterrupts
Presumablyata
ddress0xf
fyouhave
locat
edajump
instruction
whichjumps
toan
interruptserviceroutine:i.e.what
willt
heprocess
ordotoha
ndlethis
even
t
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InterruptTimin
g
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R
ETURNI
Atthe
endoftheinterruptserviceroutine,codem
ust
haveaRETURNIinstructionsothatflagsare
restored.
RET
URNIEnable
Enablesinterrupts
RET
URNIDisable
Leavesthemoff
Notet
hatinterrupts
shouldneverb
eallowedto
happe
nwhileservicinganinterrupt(i.e.thereisonly
a1-d
eepstackfor
savingtheflag
s)
Notea
lsothatregistersarenotpre
served,soyou
are
responsibleforyour
ownrun-timemodel.E.g.if
an
ISRdestroysregistercontents,the
restofthe
progra
mmustnotusethoseregisters.
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EventDr
ivenSimu
lation
TheV
HDLsimulatorisaneventdriven
simulator(veryco
mmonfordigital
simulation)
Thesimulatorhas
aqueueoftransactions
sch
eduledforthe
future,which
areprocessed
in
chr
onologicalorder
Eac
htransactioncanschedulefuturetransactions,
whichareaddedtothequeue
d
0at
t=3
f1at
t=
6
g
0at
t=6
d
1a
t
t=8
Tsim=6
Future
transactions
scheduled
execute
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VHDLSimulationTime
There
isonesimu
lationtimefortheentire
simulatedsystem
(onemasterclock).
Simulationisinde
xedbyanintegerTc.
Units
areinsecon
ds
Ad
efaultresolutionisspecifiedwhenthe
sim
ulatorisinvokedoften1nsforfunctional
sim
ulationand10
0psfortiming
simulation
(de
pendingontheresolutionof
themodelsus
ed).
Simulationtimebeginsat0s
Simulationtimeis
advancedb
ytheexecution
ofthesimu
lationcycletothetimeofthen
ext
queuedevent.
Atransactioncan
bescheduledimmediately
using
de
lta
time.
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VH
DLSimulationTerminology
Allsig
nalshavea
currentvalu
eassociated
withthematalltimesduringasimulation
Atransact
ionisanupdateofthecurrent
value
ofasignal
Durin
gasimulatio
ncycleinw
hichasignal
experiencesatransaction,the
signalissaidto
beac
tive
Anev
entisatran
sactionthat
resultsina
changeofvalue
Proce
ssescansch
eduletransa
ctionstotak
e
place
ontheirout
putsignals,bothatfuture
times
orimmediately.
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VHDLSimulationCycle
Thes
imulationcyclegovernsexecutionofthesimulation.
Thes
imulationcycleis
repeateduntilsim
ulationterminates.
Steps
inthesimulation
cycle.
1.Th
ecurrenttimeTCisassignedthenext
schedulesimulationtime
TN.
2.Ea
chactivesignalisupdatedwithitsnewvalue.
3.Processesthataresensitivetosignalsth
athavejustexperie
nced
ev
entsaremarkedto
resumeduringthe
currentsimulation
cycle,
as
wellasprocessesscheduledtoresumeatthecurrenttim
e.
4.Ea
chprocessthatism
arkedtoresumeisexecuted(innodefined
orderofprocesses)until(if)itsuspends.
5.Th
enextsimulationtimeTNiscalculated
accordingtothenext
tim
easignalissched
uletobecomeactiv
eoraprocessis
scheduledtoresume.
IfTN=
TCthenthenext
simulationcycleiscalledade
ltacycle.
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VHD
LSimulat
ionCycle,Simplified
Update
current
va
luesdue
to
transitions
at
current
simulationtime
D
etermine
w
hichsignal
upd
atescaused
events.
Evaluate
processes
sensi
tiveto
currentevents,
schedulingnew
transact
ions
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De
ltaTime
Infinitesimallysmall()advan
ceintime
Thec
urrenttimeTCdoesnotadvance
Aninfinitenumbe
rofdeltatim
estepscan
occur
betweentagsinthecurrenttimeTC
Whichdeltacycleisnotacce
sibleinthe
langu
age;dosom
ethingimm
ediatelyme
ans
doit
duringthenextcycle,wh
ichwillbea
delta
cycle
Providesameans
ofordering
aneventand
theeventsthatre
sultfromit
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More
DeltaTim
e
. . x
