Filter
Top Products
www.ti.com
PACSTRT
VCLKIN
CAPEN
VDIN[9:2] Sync Byte Byte 1 Byte 2 Byte 3 Byte 4
Start Capture
3.8.3TCICaptureErrorDetection
3.8.4SynchronizingtheSystemClock
TCICaptureMode
Figure3-15.ParallelTCICapture
ThevideoportchecksfortwotypesoferrorsduringTCIcapture.Thefirstisapacketerroronthe
incomingpacketasindicatedbyanactivePACERRsignal.IfPACERRisactiveduringanyofthefirst
eightbytesofapacketanderrorpacketfilteringisenabled(ERRFILTbitinTCICTLisset),thenthevideo
portwillignore(notcapture)theincomingdatauntilthenextPACSTRTisreceived.Iferrorpacketfiltering
isnotenabledorifPACERRbecomesactivesometimeafterthefirsteightbytesofthepacket,theentire
packetiscapturedandthePERRbitissetinthetimestampinsertedattheendofthepacket.
TheseconderrordetectedisanearlyPACSTRTerror.ThisoccurswhenanactivePACSTRTisdetected
beforeanentirepacket(asdeterminedbythepacketsizeprogrammedinVCASTOP)hasbeencaptured.
TheportwillcontinuetocapturetheexpectedpacketsizebutwillsetthePSTERRbitinthetimestamp
insertedattheendofthepacket.Aftercapturecompletion,theportwillwaitforasubsequentPACSTRT
beforebeginningcaptureofanotherpacket.
Note:WhenyouareusingTCIcapturemode,youmustclocktheSTCLKinput.Ifyoudonot
needtosynchronizetothesystemclock,youshouldclockSTCLKviatheVPxCLK0input.
Synchronizationisanimportantaspectofdecodingandpresentingdatainreal-timedigitaldatadelivery
systems.ThisisaddressedinMPEG-2transportpacketsbytransmittingtiminginformationinthe
adaptationfieldsofselecteddatapackets.Thisvalueservesasareferencefortimingcomparisoninthe
receivingsystem.Theprogramclockreference(PCR)header,showninFigure3-16,isa48-bitfield(six
bitsarereserved).A42-bitvalueistransmittedwithinthe48-bitstreamandconsistsofa33-bitPCRfield
thatrepresentsa90-kHzclocksampleanda9-bitPCRextensionfieldthatrepresentsa27-MHzclock
sample.ThePCRindicatestheexpectedtimeatthecompletionofreadingthefieldfromthebitstreamat
thetransportdecoder.Thetransportdatapacketsarein-syncwiththeencodertimeclock.
Figure3-16.ProgramClockReference(PCR)HeaderFormat
471514980
PCRReservedPCRextension
Thevideoport,inconjunctionwiththeVCXOinterpolatedcontrol(VIC),allowsacombinedhardwareand
softwaresolutiontosynchronizethelocalsystemtimeclock(STC)withtheencodertimeclockreference
transmittedinthebitstream.
Thevideoportmaintainsahardwarecounterthatcountsthesystemtime.Thecounterisdrivenbya
systemtimeclock(STCLK)inputdrivenbyanexternalVCXO.Thecounterissplitintotwofields:a33-bit
field(PCRbase)thatcountsat90kHzanda9-bitfield(PCRextension)thatcountsat27MHz.The9-bit
64VideoCapturePortSPRUEM1–May2007
SubmitDocumentationFeedback