7024SSLASHL datasheet(20/23 Pages) RENESAS

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6.42

7024S/L

High-Speed 4K x 16 Dual-Port Static RAM

Military, Industrial and Commercial Temperature Ranges

Feb.20.20

readazerointoSemaphore1.Iftherightprocessorperformsasimilartask

withSemaphore0,thisprotocolwouldallowthetwoprocessorstoswap

2K blocks of Dual-Port RAM with each other.

The blocks do not have to be any particular size and can even be

variable, depending upon the complexity of the software using the

semaphoreflags.AlleightsemaphorescouldbeusedtodividetheDual-

Port RAM or other shared resources into eight parts. Semaphores can

evenbeassigneddifferentmeaningsondifferentsidesratherthanbeing

given a common meaning as was shown in the example above.

Semaphores are a useful form of arbitration in systems like disk

interfaceswheretheCPUmustbelockedoutofasectionofmemoryduring

atransferandtheI/Odevicecannottolerateanywaitstates.Withtheuse

ofsemaphores,oncethetwodeviceshasdeterminedwhichmemoryarea

was“off-limits”totheCPU,boththeCPUandtheI/Odevicescouldaccess

theirassignedportionsofmemorycontinuouslywithoutanywaitstates.

2740 drw 20

WRITE

SEMAPHORE

REQUEST FLIP FLOP

SEMAPHORE

REQUEST FLIP FLOP

LPORT

RPORT

SEMAPHORE

READ

SEMAPHORE

READ

Figure 4. IDT7024 Semaphore Logic

Semaphoresarealsousefulinapplicationswherenomemory“WAIT”

stateisavailableononeorbothsides.Onceasemaphorehandshakehas

been performed, both processors can access their assigned RAM

segmentsatfullspeed.

Anotherapplicationisintheareaofcomplexdatastructures. Inthis

case,blockarbitrationisveryimportant.Forthisapplicationoneprocessor

mayberesponsibleforbuildingandupdatingadatastructure.Theother

processorthenreadsandinterpretsthatdatastructure.Iftheinterpreting

processorreadsanincompletedatastructure,amajorerrorconditionmay

exist.Therefore,somesortofarbitrationmustbeusedbetweenthetwo

differentprocessors.Thebuildingprocessorarbitratesfortheblock,locks

itandthenisabletogoinandupdatethedatastructure.Whentheupdate

is completed, the data structure block is released. This allows the

interpretingprocessortocomebackandreadthecompletedatastructure,

therebyguaranteeingaconsistentdatastructure.

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