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Achronix Speedster22i User Macro Guide Manual de usuario Pagina 148

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Memories BRAM80KFIFO
Speedster22i Macro Cell Library
AchronixSemiconductorProprietary PAGE 131
rdcount_sync_mode
The rdcount_sync_mode parameter defines whether the read counter (rdcount) output is
synchonous to the rdclk clock input. Assigning a value of 1’b0 to rdcount_sync_mode
configurestherdcountoutputtobesynchonizedtothewrclkclock.Assigningavalueof1’b1
to rdcount_sync_mode configures the rdcount output to be synchonized to the rdclk cl
ock.
Thedefaultvalueoftherdcount_sync_modeparameteris1’b1.
afull_offset
The afull_offset parameter defines the word depth at which the FIFO a lmost_full signal
changes. The almost_ full flag may be used to determine the number of blind writes to the
FIFO that can be made without monitoring the full flag.For example, if the afull_offset
parameterissetto17’h00004andthealmost_fullfl
agisdeasserted,theuserisguaranteedthat
thereareatleastfiveemptylocationsintheFIFO.Theusermaywriteallfivewordswithout
monitoringthefullflagand beguaranteedthatthesewordswillbe writtentotheFIFOand
thewrite_errflagwillnot beasserted.The Ma
ximumFIFO Depthisa function ofthe value
assigned to the read_width parameter as shown in Table 6‐19
: FIFO read_width versus
Maximum Read De
pth.Thedefault valueofthe afull_offsetparameteris17’h00004,corre‐
spondingtofi
veorlessavailablelocationsremainintheFIFO.
Table 6-33: Condition to Assert almost_full Flag based
on afull_offset Parameter Assignment
Mode
Condition when
almo
st_full flag is asserted
Condition when almost_full flag is
deasserted
sync_mode =
1’b0, fwft = 1’b0
afull_offset or fewer empty loca-
tions remain in the FIFO.
There are at least (afull_offset +1) empty
locations remaining in the FIFO.
sync_mode =
1’
b0, fwft = 1’b1
afull_offset or fewer empty loca-
tions remain in the FIFO.
There are at least (afull_offset +1) empty
locations remaining in the FIFO.
sync_mode =
1’
b1, fwft = 1’b0
afull_offset or fewer empty loca-
tions remain in the FIFO.
There are at least (afull_offset +1) empty
locations remaining in the FIFO.
sync_mode =
1’
b1, fwft = 1’b1
Illegal parameter combination Illegal parameter combination
aempty_offset
The aempty_offset parameter defines the word depth at which the FIFO almost_empty
changes.Thealmost_emptyflagmaybeusedtodeterminethenumberofblindreadsfromthe
FIFO that can be perfromed without monitoring the empty flag.For example, if the
aempty_offsetparameterissetto17’h0004andthealmost_emptyfl
agisdeasseted,theuseris
guaranteed that there are at leastfive words in the FIFO. The user may read all five words
withoutmonitoringtheemptyflagandbeguaranteedthatthesewordswillbereadfromthe
FIFO and the read_err flag will not be asserted.The FIFO Depth is a function of the va
lue
assigned to the read_width parameter as shown in Table 6‐19
: FIFO read_width versus
MaximumReadDe
pth.Thedefaultvalueoftheaempty_offsetparameteris17’h00004,corre‐
spondingtofou
rorlesswordsremainingintheFIFO.
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