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4.12.15VideoDisplayThresholdRegister(VDTHRLD)
VideoDisplayRegisters
Table4-19.VideoDisplayField2TimingRegister(VDFLDT2)FieldDescriptions(continued)
Bitfield
(1)
symval
(1)
ValueDescription
11-0FLD2XSTARTOF(value)0-FFFhSpecifiesthepixelonthefirstlineoffield2wheretheFLDoutputisasserted.
DEFAULT0
Thevideodisplaythresholdregister(VDTHRLD)setsthedisplayFIFOthresholdtodeterminewhento
loadmoredisplaydata.
TheVDTHRLDnbitsdetermineshowmuchspacemustbeavailableinthedisplayFIFOsbeforethe
appropriateEDMAeventmaybegenerated.TheYFIFOusestheVDTHRLDnvaluedirectlywhiletheCb
andCrvaluesuse½theVDTHRLDnvalueroundeduptothenextdoubleword(½(VDTHRLDn+
VTHRLDnmod2).TheEDMAtransfersizemustbelessthanthevalueusedforeachFIFO.Typically,
VDTHRLDnissettothehorizontallinelengthroundeduptothenextdoublewordboundary.Fornon-line
lengththresholds,thedisplaydataunpackingmechanismplacescertainrestrictionsofwhatVDTHRLDn
valuesarevalid(seeSection2.3.3).
TheVDTHRLD2bitsbehavesidenticallytoVDTHRLD1,butareusedduringfield2capture.Itisusedonly
ifthefield2EDMAsizeneedstobedifferentfromthefield1EDMAsizeforsomereason(forexample,
differentdisplaylinelengthsinfield1andfield2).
Inrawdisplaymode,theINCPIXbitsdeterminewhentheframepixelcounter(FPCOUNT)isincremented
.If,forexample,eachoutputvaluerepresentstheR,G,orBportionofadisplaypixel,thentheINCPIX
bitsaresetto3hsothatthepixelcounterisincrementedonlyoneverythirdoutputclock.AnINCPIX
valueof0hrepresentsacountof16ratherthan0.
Thevideodisplaythresholdregister(VDTHRLD)isshowninFigure4-45anddescribedinTable4-20.
Figure4-45.VideoDisplayThresholdRegister(VDTHRLD)
31262516
ReservedVDTHRLD2
R-0R/W-0
1512111090
INCPIXReservedVDTHRLD1
R/W-0001R-0R/W-0
LEGEND:R/W=Read/Write;R=Readonly;-n=valueafterreset
Table4-20.VideoDisplayThresholdRegister(VDTHRLD)FieldDescriptions
Description
Bitfield
(1)
symval
(1)
ValueBT.656andY/CModeRawDataMode
31-26Reserved-0Reserved.Thereservedbitlocationisalwaysreadas0.Avaluewrittentothisfield
hasnoeffect.
25-16VDTHRLD2OF(value)0-3FFhField2threshold.WheneverthereareatField2threshold.Wheneverthereareat
leastVDTHRLDdoublewordsofspaceleastVDTHRLDdoublewordsofspace
intheYdisplayFIFO,anewYEDMAinthedisplayFIFO,anewYEDMA
eventmaybegenerated.Whenevereventmaybegenerated.
thereareatleast½VDTHRLDdouble
wordsofspaceintheCborCrdisplay
FIFO,anewCborCrEDMAeventmay
begenerated.
DEFAULT0
15-12INCPIXOF(value)0-FhNotused.FPCOUNTisincrementedeveryINCPIX
outputclocks.
DEFAULT1
(1)
ForCSLimplementation,usethenotationVP_VDTHRLD_field_symval
SPRUEM1–May2007VideoDisplayPort137
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