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3.13.8VideoCaptureChannelxThresholdRegister(VCATHRLD,VCBTHRLD)
VideoCaptureRegisters
Thevideocapturechannelxthresholdregister(VCATHRLD,VCBTHRLD)determineswhenEDMA
requestsaresent.
TheVCTHRLD1bitsdeterminewhencaptureEDMAeventsaregenerated.Oncethethresholdis
reached,generationoffurtherEDMAeventsisdisableduntilserviceofthepreviousevent(s)begins(the
firstFIFOreadbytheEDMAoccurs).
InBT.656andY/Cmodes,everytwocapturedpixelsrepresent2lumavaluesintheYFIFOand2chroma
values(1eachintheCbandCrFIFOs).Dependingonthedatasizeeachvaluemaybeabyte(8-bit
BT.656orY/C)withintheFIFOs.Therefore,theVCTHRLD1doublewordnumberrepresents8pixelsin
8-bitmodes.SincetheCbandCrFIFOthresholdsarerepresentedby½VCTHRLD1,certainrestrictions
areplacedonwhatVCTHRLD1valuesarevalid(seeSection2.3.3).
Inrawdatamode,eachdatasamplemayoccupyabyte(8-bitrawmode),2bytes(16-bitrawmode),
withintheFIFO,dependingonthedatasize.Therefore,theVCTHRLD1doublewordnumberrepresents8
samples,4samplesrespectively.
InTCImode,VCTHRLD1representsgroupsof8sampleswitheachsampleoccupyingabyteintheFIFO.
TheVCTHRLD2bitsbehaveidenticallytoVCTHRLD1,butareusedduringfield2capture.Itisonlyused
ifthefield2EDMAsizeneedstobedifferentfromthefield1EDMAsizeforsomereason(forexample,
differentcapturedlinelengthsinfield1andfield2).IfVT2ENisnotset,thentheVCTHRLD1valueis
usedforbothfields.
NotethattheVCTHRLDnappliestodatabeingwrittenintotheFIFO.Inthecaseof8-bitBT.656orY/C
modes,thismeanstheoutputofanyselectedfilter.
Thevideocapturechannelxthresholdregister(VCxTHRLD)isshowninFigure3-28anddescribedin
Table3-21.
Figure3-28.VideoCaptureChannelxThresholdRegister(VCxTHRLD)
31262516
ReservedVCTHRLD2
R-0R/W-0
151090
ReservedVCTHRLD1
R-0R/W-0
LEGEND:R/W=Read/Write;R=Readonly;-n=valueafterreset
Table3-21.VideoCaptureChannelxThresholdRegister(VCxTHRLD)FieldDescriptions
Description
Bitfield
(1)
symval
(1)
ValueBT.656orY/CModeRawDataModeTCIMode
31-26Reserved-0Reserved.Thereservedbitlocationisalwaysreadas0.Avaluewrittentothis
fieldhasnoeffect.
25-16VCTHRLD2OF(value)0-3FFhNumberoffield2doublewordsNotused.Notused.
requiredtogenerateEDMA
events.
DEFAULT0
15-10Reserved-0Reserved.Thereservedbitlocationisalwaysreadas0.Avaluewrittentothis
fieldhasnoeffect.
9-0VCTHRLD1OF(value)0-3FFhNumberoffield1doublewordsNumberofrawdataNumberofdouble
requiredtogenerateEDMAdoublewordsrequiredwordsrequiredto
events.togenerateaEDMAgenerateaEDMA
event.event.
DEFAULT0
(1)
ForCSLimplementation,usethenotationVP_VCxTHRLD_VCTHRLDn_symval
80VideoCapturePortSPRUEM1–May2007
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