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5.4.5InterruptLatency
5.5TMS320C55xRulesandGuidelines
5.5.1StackArchitecture
5.5.2DataModels
TMS320C55xRulesandGuidelines
ST1FieldNameUseType
INTMInterruptmaskPreserve(global)
OVMOverflowmodebitPreserve(local)
SXMFractionalmodebitScratch(local)
XFExternalFlagScratch(global)
ThePMSTregisterisusedtocontroltheprocessormodeandisoftypeInit.
PMSTFieldNameUseType
AVISAddressVisibilitybitRead-only(global)
CLKOFFCLKOUTdisablebitRead-only(global)
DROMMapROMintodataspaceRead-only(local)
IPTRInterruptVectorTablePointerRead-only(global)
MP/MCMicroprocessor/microcomputermodebitRead-only(global)
OVLYRAMOverlaybitRead-only(local)
SMULSaturationonmultiplybitInit(local)
SSTSaturationonstoreInit(local)
AlthoughtherearenoadditionalrulesforC54xalgorithmsthatdealwithinterruptlatency,itisimportantto
notethatallRPTandRPTZloopsarenon-interruptible;i.e.,oncestarted,interruptsareblockeduntilthe
entireloopcompletes.Thus,thelengthoftheseloopscanhaveasignificanteffectontheworstcase
interruptlatencyofanalgorithm.
ThissectiondescribestherulesandguidelinesthatarespecifictotheTMS320C5500familyofDSPs.
TheC55XCPUsupportsdifferentstackconfigurationsandthestackconfigurationregister(4bits)selects
thestackarchitecture.Theselectionofthestackarchitecturecanbedoneonlyonahardwareorsoftware
reset.Tofacilitateintegration,eachalgorithmmustpublishthestackconfigurationthatituses.
Rule31
AllC55xalgorithmsmustdocumentthecontentofthestackconfigurationregisterthattheyfollow.
Guideline14
AllC55xalgorithmsshouldnotassumeanyspecificstackconfigurationandshouldworkunderallthe
threestackmodes.
TheC55Xcompilersupportsasmallmemorymodelandalargememorymodel.Thesememorymodels
affecthowdataisplacedinmemoryandaccessed.Theuseofasmallmemorymodelresultsincodeand
datasizesthatareslightlysmallerthanwhenusingthelargememorymodel.However,thisimposes
certainconstraintsonthesizeandmemoryplacement.Inthesmallmemorymodel,thetotalsizeofthe
directlyaccesseddatainanapplicationmustallfitwithinasinglepageofmemorythatis64Kwordsin
size.Sincealgorithmsareagnosticofwheretheyaregoingtobeinstanced;allglobalandstaticdata
referencesshouldbefarreferences.
52DSP-SpecificGuidelinesSPRU352G–June2005–RevisedFebruary2007
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