User Macro Guide

Table Of Contents
Memories LRAMFIFO
Speedster22i Macro Cell Library
AchronixSemiconductorProprietary PAGE 163
transferringtheReadPointeracrossclockdomains.Asanexample,settingrdptr_sync_stages
to2’b00configuresthereadpointersynchronizationcircuittohavetwobacktobackregisters
in the Read Pointer Synchonizer.The default value of the rdptr_sync_stages parameter is
2’b00.
Table 6-53: Mapping rdptr_sync_stages Parameter Settings to S
ynchronization Stage Depth
rdptr_sync_stages Read Pointer Synchronization Stage Depth
2’b00 2
2’b01 3
2’b10 4
2’b11 5
Figure 6-34: Read P
ointer Synchronizer Block Diagram
rst_sync_mode
Therst_sync_modeparameteraffectsthebehavioroftheresetoperationofthewriteandread
pointers.Whentherst_sync_modeparameterissetto1’b0,boththereadandwritepointers
resets utilize the Reset Synchronizer circuitry. When the rst_sync_mode parameter is set to
1’b1therstninputmustbesynchronoustothewrcl
k/rdclkclockdrivingtheFIFO.Thedefault
valueoftherst_sync_modeparameteris1’b0.
wrrst_sync_stages
The wrrst_sync_stages parameter defines the number of stages of registers used to
synchronizetherstninputpintotherdclkclockdomain.Thevalueofthewrrst_sync_stages
parameter is only used if the rst_sync_mode is set to 1’b0.The mapping of the
wrrst_sync_stagesparametervaluetothenumberofsychronizationstagesisdef
inedinTable
654: Mapping w
rrst_sync_stages Parameter Settings to Synchronization Stage Depth,
where each st
age corresponds to a register in Figure 635: Write Pointer Reset Input
SelectionBlockDiagram.Forexample,set
tingwrrst_sync_stagesto2’b00configurestherstn
synchronizationcircuittohav
etwobacktobackregistersintheWriteResetSynchonizer.The
defaultvalueofthewrrst_sync_stagesparameteris2’b00.
Table 6-54: Mapping wrrst_sync_stages Parameter Settings to S
ynchronization Stage Depth
wrrst_sync_stages Write Reset Synchronization Stage Depth
2’b00 2
2’b01 3
2’b10 4
2’b11 5
Read
Pointer
Read Pointer Synchronizer
d
q
d
q
d
q
d
q
d
q
rdclk
wrclk
ptr_sync_mode
rdptr_sync_stages
Synchronized
Read Pointer
used for flag
00
01
10
11
0
1
calculations