Achronix Speedster22i User Macro Guide Instrukcja Użytkownika Pobierz pdf (Strona 148)

Memories BRAM80KFIFO

Speedster22i Macro Cell Library

AchronixSemiconductorProprietary 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

configurestherdcountoutputtobesynchonizedtothewrclkclock.Assigningavalueof1’b1

to rdcount_sync_mode configures the rdcount output to be synchonized to the rdclk cl

ock.

Thedefaultvalueoftherdcount_sync_modeparameteris1’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

parameterissetto17’h00004andthealmost_fullfl

agisdeasserted,theuserisguaranteedthat

thereareatleastfiveemptylocationsintheFIFO.Theusermaywriteallfivewordswithout

monitoringthefullflagand beguaranteedthatthesewordswillbe writtentotheFIFOand

thewrite_errflagwillnot beasserted.The Ma

ximumFIFO Depthisa function ofthe value

assigned to the read_width parameter as shown in Table 6‐19

: FIFO read_width versus

Maximum Read De

pth.Thedefault valueofthe afull_offsetparameteris17’h00004,corre‐

spondingtofi

veorlessavailablelocationsremainintheFIFO.

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.Thealmost_emptyflagmaybeusedtodeterminethenumberofblindreadsfromthe

FIFO that can be  perfromed without monitoring the empty flag.For example, if the

aempty_offsetparameterissetto17’h0004andthealmost_emptyfl

agisdeasseted,theuseris

guaranteed that there are at leastfive words in the FIFO. The user may read all five words

withoutmonitoringtheemptyflagandbeguaranteedthatthesewordswillbereadfromthe

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

MaximumReadDe

pth.Thedefaultvalueoftheaempty_offsetparameteris17’h00004,corre‐

spondingtofou

rorlesswordsremainingintheFIFO.

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