Achronix Speedster22i User Macro Guide Manual do Utilizador descarregar pdf (Página 154)

Memories BRAM80KFIFO

Speedster22i Macro Cell Library

AchronixSemiconductorProprietary PAGE 137

FIFO Operational Modes

TheFIFOmacrosupportsbothsingleclocksynchronous(sameclockconnectedtowrclkand

rdclkinputswithout anyphaseoffsetbetweenthetwoclocks) anddualclock asynchronous

(twounrelatedclocksortworelatedclocks)modesofoperation.Forsynchronousoperation,

both the wrclk and rdclk  inputs must be connected  to

 the same clock net.Phase offsets

between the two clocks in synchronous mode is not allowed.For asynchronous mode, the

usermayconnectthewrclkandrdclkinputstotwodifferentclocks.TheFIFOwilltreatthe 

twoclocksasiftheyareunrelated.

Asynchronous FIFO Operation

When the FIFO is configured as an asynchronous FIFO (sync_mode = 1’b0), there are two

modesofoperationavailable.ThetwomodesoftheFIFOiscontrolledbytheFirstWordFall

Through(fwft)parameter.ThisparametercontrolswhatisontheoutputoftheFIFOafterthe

firstwordhas

beenwri tten toaFIFOthatwaspreviouslyinanemptystate.Forasynchronous

operation,theusermustsettheen_out_regparameterto1’b1.

Asychronous FIFO Standard Mode (sync_mode = 1’b0, fwft = 1’b0)

Afteraresetoperation,orafterthelastwordhasbeenreadfromtheFIFO,theFIFOwillbein

an empty state as indicated by a high level on the empty flag.When the FIFO in set to

standardmode(fwft= 1’b0),theoutputoftheFIFOremainsunchanged

afterthefirstwriteto

a FIFO in the empty state.After the first writeoperation the empty flag will be deasserted

indicating that there isdatain the FIFOthatmaybe read.The usermustread theFIFOby

settingtherdenhighatwhichtimethefirst

wordwrittenintotheFIFOwillbeavailableatthe

FIFO outputs at the next rising edge of the rdclk input.Each subsequent read operation

updatestheFIFOoutputswiththe nextstoreddatawordifitisavailable(emptyflag=false).

Asychronous FIFO First Word Fall Through Mode (sync_mode = 1’b0, fwft = 1’b1)

Afteraresetoperation,orafterthelastwordhasbeenreadfromtheFIFO,theFIFOwillbein

anemptystateasindicatedbyahighlevelontheemptyflag.WhentheFIFOinsettoFirst

WordFallThroughmode(fwft=1’b1),theoutputofthe

FIFOwillbeupdatedafterthefirst

write to a FIFO in the empty state.After the first write operation the empty flag will be

deasserted indicating that there is data in the FIFO that may be read.In First Word Fall

Throughmode,thefirstwordwrittenintothe

FIFOisplacedonthe FIFOoutputsbeforethe

firstreadoperation occurs.Eachsubsequent read operationupdatesthe FIFOoutputswith

thenextstoreddatawordifitisavailable(emptyflag=1’b0).NotethatwhenselectingFirst

Word Fall Through mode, the FIFO must be configured for asynchronous

 operation

(sync_mode = 1’b0).First Word Fall Through mode is not supported when the FIFO is

configuredforsynchronousFIFOoperation(sync_mode=1’b1).

Synchronous FIFO Operation

The synchronous FIFO mode supports the standard mode.The First Word Fall Through

modeisnotsupportedwhensynchronous FIFOoperationisselected.Theusermustnotset

thefwftparameterto1’b1whensynchronousFIFOoperationisselected.Theusermayeither

allowtheFIFOtopickupthedefault

valueofthefwftparameter(1’b0)orsetitto1’b0.

Synchronous FIFO Standard Mode (sync_mode = 1’b1)

Thesynchronous FIFO standardmodehas the advantagethatthereisnolatencyin theflag

calculations, so the  flags represent the exact state of the FIFO.In sycnchronous mode, the

Reset

Output

“regce” 1 1



reg_srval

Operation regce_priority rstreg outregce rdclk dout

1 2 ... 149 150 151 152 153 154 155 156 157 158 159 ... 223 224

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