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7.3ClockManagement
7.3.1ModuleClockON/OFF
7.3.2ModuleClockFrequencyScaling
7.3.3PLLBypassandPowerDown
ClockManagement
Themoduleclockon/offfeatureallowssoftwaretodisableclockstomoduleindividually,inordertoreduce
themodule'sactivepowerconsumptionto0.TheDM643xDMPisdesignedinfullstaticCMOS;thus,
whenamoduleclockstops,themodule'sstateispreserved.Whentheclockisrestarted,themodule
resumesoperatingfromthestoppingpoint.
Note:Stoppingclockstoamoduleonlyaffectsactivepowerconsumption,itdoesnotaffect
leakagepowerconsumption.
Ifamodule'sclock(s)isstoppedwhilebeingaccessed,theaccessmaynotoccur,andcouldpotentially
lock-upthedevice.Usermustensurethatallofthetransactionstothemodulearefinishedpriorto
stoppingtheclocks.Thepowerandsleepcontroller(PSC)controlsmoduleclockgating.ThePSC
providessomeprotectionagainstsystemhangbymonitoringtheinternalbusactivity—itonlygates
internalclocktothemoduleaftercheckingthatthereisnoaccesstothemodulefromtheinternalbus.
Theproceduretoturnmoduleclockson/offusingthePSCisdescribedinChapter6.Furthermore,special
considerationmustbegiventoDSPclockon/off.TheproceduretoturntheDSPclockon/offisfurther
describedinSection7.4.2.
Someperipheralsprovideadditionalpowersavingfeaturesbyclockgatingcomponentswithinitsmodule
boundary.Seeperipheral-specificuser'sguideformoredetailsontheseadditionalpowersavingfeatures.
ModuleclockfrequencyisscalablebyprogrammingthePLL'smultiplyanddivideparameters.Reducing
theclockfrequencyreducestheactiveswitchingpowerconsumptionlinearlywithfrequency.Ithasno
impactonleakagepowerconsumption.
Chapter4andChapter5describethehowtoprogramthePLLfrequencyandthefrequencyconstraints.
YoucanbypassthePLLsintheDM643xDMP.BypassingthePLLssendsthePLLreferenceclock
(MXI/CLKIN)insteadofthePLLoutput(PLLOUT)totheSYSCLKdividers(PLLDIVn)ofthePLLC.The
PLLreferenceclockistypicallyat27MHZ;therefore,youcanusethismodetoreducethecoreand
moduleclockfrequenciestoverylowmaintenancelevelswithoutusingthePLLduringperiodsofverylow
systemactivity.Furthermore,youcanpower-downthePLLwhenbypassingittosaveadditionalactive
power.
Chapter4andChapter5describePLLbypassandPLLpowerdown.
SPRU978E–March2008PowerManagement79
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