Achronix Speedster22i User Macro Guide Manuel d'utilisateur télécharger pdf (Page 150)

Memories BRAM80KFIFO

Speedster22i Macro Cell Library

AchronixSemiconductorProprietary PAGE 133

Read and Write Count Outputs

Write Count Output

The Write Count  (wrcount) output of the FIFO shows the value of the Write Pointer . The

wrcount may be synchronized to either the wrclk or rdclk clock domains by setting the

wrcount_sync_mode parameter bit.Setting the wrcount_sync_mode parameter to 1’b1

outputsthewrcountdirectlyfromtheWritePointer(synchronoustothe

wrclkclock).Setting

thewrcount_sync_modeto1’b0outputsthewrcountsynchronoustotherdclkoutputafterit

has been synchronized to the rdclk clock through a synchonization circuit that is

wrptr_sync_stages + 2 registers deep.Note that if the Write Pointer is synchronized to the

rdclkclockdomain,thevalue

oftheWriteCounterwillbe delayedandhavearateofchange

that will vary dependent on the rdclk clock rate.

Figure 6‐10: Write Pointer Synchronizer

BlockDiagramshowstheWriteCount OutputCircuit.

Figure 6-10: Write Pointer Synchronizer Block Diagram

Read Count Output

The Read Count (rdcount) output of the FIFO shows the  value of the Read Pointer. The

rdcount may be synchronized to either the wrclk or rdclk clock domains by setting the

rdcount_sync_mode parameter bit.Setting the rdcount_sync_mode parameter to 1’b1

outputstherdcountdirectlyfromtheReadPointer(synchronoustothe

rdclkclock).Setting

the rdcount_sync_mode parameter to 1’b0 outputs the rdcount synchronous to the wrclk

outputafterithasbeensynchronizedtothewrclkclockthroughasynchonizationcircuitthat

isrdptr_sync_stages +2 registersdeep.Notethatifthe ReadPointeris synchronizedtothe

wrclkclockdomain,the

valueofthe ReadCounterwillbedelayedandhavearateofchange

that will vary dependent on the wrclk clock  rate.

Figure 6‐11: Read Pointer Synchronizer

BlockDiagramshowstheReadCountOutputCircuit.

Figure 6-11: Read Pointer Synchronizer Block Diagram

Write

Pointer

Write Pointer Synchronizer

wrcount

wrclk

rdclk

wrcount_sync_mode

wrptr_sync_stages

Synchronized

Write Pointer

used for flag

calculations

Read

Pointer

Read Pointer Synchronizer

rdcount

rdclk

wrclk

rdcount_sync_mode

rdptr_sync_stages

Synchronized

Read Pointer

used for flag

calculations

1 2 ... 145 146 147 148 149 150 151 152 153 154 155 ... 223 224

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Achronix Speedster22i User Macro Guide Manuel d'utilisateur Page 150

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