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4.7.2VideoDisplayEventGeneration
4.8DisplayLineBoundaryConditions
DisplayLineBoundaryConditions
Table4-4.DisplayOperation(continued)
VDCTLBit
CONFRAMEDF2DF1Operation
0111Singleframedisplay.Displaybothfields.FRMDissetafterfield2displayand
causesDCMPxtobeset.ADCNAinterruptoccursunlesstheFRMDbitis
cleared.(TheDSPhasthefield2tofield1verticalblankingtimetoclear
FRMD.)
1000Reserved
1001Continuousfield1display.Displayonlyfield1.F1Dissetafterfield1display
andcausesDCMPxtobeset(DCMPxinterruptcanbedisabled).NoDCNA
interruptoccurs,regardlessofthestateofF1D.
1010Continuousfield2display.Displayonlyfield2.F2Dissetafterfield2display
andcausesDCMPxtobeset(DCMPxinterruptcanbedisabled).NoDCNA
interruptoccurs,regardlessofthestateofF2D.
1011Reserved
1100Continuousframedisplay.Displaybothfields.FRMDissetafterfield2display
andcausesDCMPxtobeset(DCMPxinterruptcanbedisabled.NoDCNA
interruptoccurs,regardlessofthestateofFRMD.
1101Continuousprogressiveframedisplay.Displayfield1.FRMDissetafterfield1
displayandcausesDCMPxtobeset(DCMPxinterruptcanbedisabled).No
DCNAinterruptoccurs,regardlessofthestateofFRMD.(Functionsidentically
tocontinuousfield1displaymodeexcepttheFRMDbitisusedinsteadofthe
F1Dbit.)Ifexternalcontrolsignalsareused,theymustfollowprogressive
format.
1110Reserved
1111Reserved
ThedisplayFIFOsarefilledusingEDMAsasrequestedbythevideoportEDMAevents.TheVDTHRLD
valueindicatesthelevelatwhichtheFIFOhasenoughroomtoreceiveanotherEDMAblockofdata.
DependingonthesizeoftheEDMA,theFIFOmayhaveroomformultipletransfersbeforereachingthe
VDTHRLDlevel.Oncethethresholdisreached,anotherEDMAeventisgeneratedassoonastheFIFO
againfallsbelowtheVDTHRLDlevel.
OnceanentirefieldworthofdatahasbeensenttotheFIFO,thevideoportmayneedtostopgenerating
eventsinordertoallowtheDSPtochangeEDMA.Sincedisplaymaynotyetbecomplete(theFIFO
continuestoemptyafterfallingbelowVDTHRLD),adisplayeventcounter(DEVTCT)isprovidedtotrack
thenumberofrequestedYEVTevents.Thecounterisloadedwiththenumberofeventsneededina
displayfield(DISPEVT1orDISPEVT2)andisdecrementedeachtimetheeventisrequested.Oncethe
counterreaches0,furtherdisplayeventsareinhibited.Atthestartofthenextfield,DEVTCTisreloaded
anddisplayeventsarereenabled.
InordertosimplifyEDMAtransfers,FIFOdoublewordsdonotcontaindatafrommorethanonedisplay
line.ThismeansthataFIFOreadmustbeperformedwhenever8-byteshavebeenoutputorwhenthe
linecompletecondition(IPCOUNT=IMGHSIZE)occurs.Thus,everydisplaylinebeginsonadoubleword
boundaryandnon-doublewordlengthlinesaretruncatedattheend.AnexampleisshowninFigure4-24.
InFigure4-24(8-bitY/Cmode),thelinelengthisnotadoubleword.WhentheconditionIPCOUNT=
IMGHSIZEoccurs,theremainingbytesoftheFIFOdoublewordareignoredandtheoutputswitchesto
thedefaultoutputvalue(ortheEAVcodefollowedbyblanking,iftheendoftheactivevideolinehasbeen
reached).ThenextdisplaylinethenbeginsinthenextFIFOlocationatbyte0.Thisoperationextendsto
alldisplaymodes.
SPRUEM1–May2007VideoDisplayPort109
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