2.17PowerManagement
2.18EmulationConsiderations
Architecture
EachofthethreemaincomponentsoftheEMACperipheralcanindependentlybeplacedin
reduced-powermodestoconservepowerduringperiodsoflowactivity.Thepowermanagementofthe
EMACperipheraliscontrolledbytheprocessorPowerandSleepController(PSC).ThePSCactsasa
mastercontrollerforpowermanagementonbehalfofalloftheperipheralsonthedevice.
ThepowerconservationmodesavailableforeachofthethreecomponentsoftheEMAC/MDIO
peripheralare:
•Idle/Disabledstate.Thismodestopstheclocksgoingtotheperipheral,andpreventsalltheregister
accesses.Afterreenablingtheperipheralfromthisidlestate,alltheregistersvaluespriortosetting
intothedisabledstatearerestored,anddatatransmissioncanproceed.Noreinitializationis
required.
•Synchronizedreset.ThisstateissimilartothePower-onReset(POR)state,whentheprocessoris
turned-on;resettotheperipheralisasserted,andclockstotheperipheralaregatedafterthat.The
registersareresettotheirdefaultvalue.Whenpowering-upafterasynchronizedreset,allthe
EMACsubmodulesneedtobereinitializedbeforeanydatatransmissioncanhappen.
FormoreinformationontheuseoftheprocessorPowerandSleepController(PSC),seethe
TMS320DM646xDMSoCARMSubsystemReferenceGuide(SPRUEP9).
Note:Forcorrectoperation,theEMACandEMACcontrolmodulemustbothbesuspended.
Thus,theEMCONTROLandCMEMCONTROLregistersmustbeconfiguredalike.
EMACemulationcontrolisimplementedforcompatibilitywithotherperipherals.TheSOFTandFREE
bitsintheemulationcontrolregister(EMCONTROL)allowEMACoperationtobesuspended.
Additionally,emulationcontrolisalsoimplementedintheEMACcontrolmodulewiththeEMACcontrol
moduleemulationcontrolregister(CMEMCONTROL)toallowtheEMACcontrolmoduleactivitytobe
suspended.
Whentheemulationsuspendstateisentered,theEMACstopsprocessingreceiveandtransmitframes
atthenextframeboundary.Anyframecurrentlyinreceptionortransmissioniscompletednormally
withoutsuspension.Fortransmission,anycompleteorpartialframeinthetransmitcellFIFOis
transmitted.Forreceive,framesthataredetectedbytheEMACafterthesuspendstateisenteredare
ignored.Nostatisticsarekeptforignoredframes.
Table8showshowtheSOFTandFREEbitsaffecttheoperationoftheemulationsuspend.
Table8.EmulationControl
SOFTFREEDescription
00Normaloperation
10Emulationsuspend
X1Normaloperation
60EthernetMediaAccessController(EMAC)/ManagementDataInput/Output(MDIO)SPRUEQ6–December2007
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