Filter
Top Products
www.ti.com
4.11.1HandlingUnder-runConditionoftheDisplayFIFO
DisplayingVideoinRawDataMode
bytotaldoublewordsperYEDMA.
20.WritetoVPIEtoenableunder-run(DUND)anddisplaycomplete(DCMP)interrupts,ifdesired.
21.WritetoVDTHRLDtosetthedisplayFIFOthreshold(VDTHRLDbits)andtheFPCOUNTincrement
rate(INCPIXbit).
22.WritetoVDCTLto:
•Setdisplaymode(DMODE=01xfor8-bitoutput,11xfor16bitoutput).
•Setdesiredfield/frameoperation(CON,FRAME,DF1,DF2bits).
•Selectcontroloutputs(VCTL1S,VCTL2S,VCTL3Sbits)orexternalsyncinputs(HXS,VXS,FXS
bits).
•Select10-bitunpackingmode(DPKbit),ifappropriate.
•SetVDENbittoenablethedisplay.
23.Waitfor2ormoreframetimes,toallowthedisplaycountersandcontrolsignalstobecomeproperly
synchronized.
•InVPIE,pollfordisplaycomplete(DCMP)interrupts.
•WritetoclearDCMP.
•PollforDCMPagain.
•WritetoclearDCMPagain.
24.WritetoVDCTLtocleartheBLKDISbit.
25.Setthevideodisplayfield1timing.Specifythefirstlineandpixeloffield1inVDFLDT1.
26.DisplayisenabledatthestartofthefirstframeafterBLKDIS=0andbeginswiththefirstselected
field.EDMAeventsaregeneratedastriggeredbyVDTHRLDandtheDEVTCTcounter.Whena
selectedfieldhasbeendisplayed(FLCOUNT=FRMHEIGHTandFPCOUNT=FRMWIDTH),the
appropriateF1D,F2D,orFRMDbitsaresetandcausetheDCMPbitinVPIStobeset.Thisgenerates
aDSPinterrupt,iftheDCMPbitisenabledinVPIE.
27.Ifcontinuousdisplayisenabled,thevideoportbeginsdisplayingagainatthestartofthenextfieldor
frame.Ifnoncontinuousfield1andfield2orframedisplayisenabled,thenextfieldorframeis
displayed,duringwhichtheDSPmustcleartheappropriatecompletionstatusbitoraDCNAinterrupt
occursandincorrectdatamaybeoutput.
AFIFOunder-runoccurswhenthedisplayFIFOisemptyduringanactivedisplaylinebecauseapending
EDMArequestfailedtoloadthedataintime.IncaseofaFIFOunder-runcondition,theDUNDbitinVPIS
isset.ThisconditioninitiatesaninterrupttotheDSP,iftheunder-runinterruptisenabled(theDUNDbitin
VPIEisset).
Becausevideodisplayistypicallyacontinuousreal-timeoutput,dataoutputisnothaltedwhenaFIFO
under-runoccurs.(Tooutputablankingofdefaultvalueisjustascatastrophictoadisplayasoutputting
anolddatavalue.)Instead,theFIFOreadpointercontinuestoadvanceand(old)datacontinuestobe
outputfromtheFIFO.ThismeansthatifthependingEDMAisonlyslightlylate,thedatatransferhasa
chancetocatchtheFIFObackuptothereadpointerandcorrectdataoutputresumes.Ifthepending
EDMAdoesnotcompleteservicewithinathreshold'sworthofoutputdata,thentheEDMArequest
sequenceisbrokenandtheremainderofthedisplayfieldiscorrupted.
Theunder-runinterruptroutineshouldsettheBLKDISbitinVDCTLanditshouldreconfiguretheEDMA
channelsettings.SettingtheBLKDISbitflushesthechanneldisplayFIFOandpreventschannelEDMA
eventsfromreachingtheEDMAcontroller.TheEDMAmustbereconfiguredcorrectlyforthenextframe
displaysincethecurrentframetransferfailed.Theframelineandframepixelcounterscontinuecounting
and,fromapinstandpoint,thevideodisplaymoduleappearstocontinuetofunctionnormally(SAV/EAV
codesaregeneratedintheBT.656orY/Cmodeandthedefaultdatavalueissentout).TheBLKDISbit
shouldthenbeclearedtoreenableEDMAevents.ClearingtheBLKDISbitdoesnotenableEDMAevents
duringtheframewherethebitiscleared.ClearingthisbittozeroenablesEDMAeventsintheframethat
followstheframewherethebitiscleared.
SPRUEM1–May2007VideoDisplayPort121
SubmitDocumentationFeedback