2.3.4EDMAInterfaceOperation
2.4VideoPortControlRegisters
VideoPortControlRegisters
Whenthevideoportisconfiguredforcapture(orTCI)mode,itonlyacceptsreadrequestsfromtheEDMA
interface.Writerequestsarefalseacknowledged(sothebusdoesnotstall)andthedataisdiscarded.
Whenthevideoportisconfiguredfordisplaymode,itonlyacceptswriterequests.Readrequestsare
falseacknowledged(sothebusdoesnotstall)andanarbitrarydatavalueisreturned.
Whenthevideoportisinreset,isnotenabled(PERENbitcleared),halted(VPHALTbitisset),orthe
activemodeisnotenabled(VCENorVDENbitiscleared),thentheportwillfalseacknowledgeallEDMA
accessestopreventbuslockup.
ThevideoportEDMAeventgenerationlogicisverytightlycoupledtotheEDMAinterfaceaccesses.An
incorrectlyprogrammedEDMAsizecausestheEDMAandFIFOtobecomemisalignedcausing
aberrationsinthecapturedordisplayeddataandlikelyresultinginaneventualFIFOoverflowor
underflow.Inthesamemanner,ifanothersystemEDMAincorrectlyaddressesthevideoportduring
activecaptureordisplay,thevideoporthasnowayofdeterminingthatthisisanerrantEDMAbecauseall
itmonitorsisaEDMAaccesssoitmustperformtheFIFOreadorwrite.SuchanerrantEDMAeventually
causestheFIFOtobeover-readoroverwritten.
ThevideoportcontrolregistersarelistedinTable2-1.Seethedevice-specificdatasheetforthememory
addressoftheseregisters.
Table2-1.VideoPortControlRegisters
Offset
Address
(1)
AcronymRegisterNameSection
C0hVPCTLVideoPortControlRegisterSection2.4.1
C4hVPSTATVideoPortStatusRegisterSection2.4.2
C8hVPIEVideoPortInterruptEnableRegisterSection2.4.3
CChVPISVideoPortInterruptStatusRegisterSection2.4.4
(1)
Theabsoluteaddressoftheregistersisdevice/portspecificandisequaltothebaseaddress+offsetaddress.Seethe
device-specificdatasheettoverifytheregisteraddresses.
VideoPort 34SPRUEM1–May2007
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