Achronix Speedster22i User Macro Guide Manual do Utilizador descarregar pdf (Página 160)

Memories BRAM80KFIFO

Speedster22i Macro Cell Library

AchronixSemiconductorProprietary PAGE 143

Writing to an Almost Full FIFO (en_wr_when_full = 1’b0)

Figure 6-16: Writing to an Almost Full FIFO (en_wr_when_full = 1’b0)

Writing to an Almost Full FIFO (en_wr_when_full = 1’b1)

Figure 6-17: Writing to an Almost Full FIFO (en_wr_when_full = 1’b1)

wrclk

rdclk

wren

rden

din

almost_full

write_err

1. Almost Full Offset programmed for 5 40-bit words (aempty_offset = 17’h00004)

Note: This timing diagram assumes:

2. wptr_sync_stages = 2’b00

3. en_wr_when_empty = 1’b0

wrd 2042 wrd 2043

wrd 2044 wrd 2045

full

wrd 2046

wrd 2047

wrd 2048

A B C D

Event : Finish writing 2049 words to the FIFO.

Event : The almost_full flag is asserted.

Event : The full flag is asserted four write cycles after almost_full flag is asserted (assuming no reads).

Event : The write_err flag is asserted one wrclk cycle after attempting to write a full FIFO.

wrclk

rdclk

wren

rden

din

Note: This timing diagram assumes:

1. wptr_sync_stages = 2’b00

2. en_wr_when_empty = 1’b0

wrd 2048 wrd 2049

A D

Event : In process of writing 2050 (wrd 0 through wrd 2049) words to the FIFO.

Event : The 2049th (wrd 2048) word is written to the FIFO. The first word (wrd 0) is overwritten

4. write_width = 40 and read_width = 40, implying a maximum FIFO depth of 2048 locations

by the 2049th word since en_wr_when_empty = 1’b1 and the maximum depth of the

FIFO is 2048 words.

5. After the FIFO was reset, a sequence of 2049 writes (wrd 0 through wrd 2048) to the FIFO occurs.

wrd 2048

wrd 2049 wrd 2

3. fwft = 1’b0

dout

Event : Begin reading FIFO from location 0.

B C E F G

Event : The 2050th (wrd 2049) word is written to the FIFO. The second word (wrd 1) is overwritten

by the 2050th word.

Event : First word read is wrd 2048 that overwrote wrd 0.

Event : Third word read is wrd 3.

Event : Second word read is wrd 2049 that overwrote wrd 1.

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