Achronix Speedster22i User Macro Guide - Manual (Page 149)

Memories BRAM80KFIFO
Speedster22i Macro Cell Library Achronix Semiconductor Proprietary PAGE 132
Table 6-34: Condition to Assert almost_empty Flag based on afull_offset Parameter Assignment
Mode
Condition when
almost_empty flag is
asserted
Condition when almost_empty flag is
deasserted
sync_mode =
1’b0, fwft = 1’b0 aempty_offset or fewer
words remain in the FIFO. There are at least (aempty_offset +1) words in
the FIFO.
sync_mode =
1’b0, fwft = 1’b1 (aempty_offset + 1) or fewer
words remain in the FIFO. There are at least (aempty_offset +1) words in
the FIFO, plus the word fallen through to the
output.
sync_mode =
1’b1, fwft = 1’b0 aempty_offset or fewer
words remain in the FIFO. There are at least (aempty_offset +1) words in
the FIFO.
sync_mode =
1’b1, fwft = 1’b1 Illegal parameter combina-
tion Illegal parameter combination
wren_polarity_sel
The wren_polarity_sel parameter allows the user to set the active level of the wren input
signal. When wren_polarity_sel is set to 1’b0 the wren input is active‐low. When
wren_polarity is set to 1’b1 the wren input is active‐high. The default value of the
wren_polarity_sel parameter is 1’b1.
rden_polarity_sel
The rden_polarity_sel parameter allows the user to set the active level of the rden input signal.
When rden_polarity_sel is set to 1’b0 the rden input is active‐low. When rden_polarity is set to
1’b1 the rden input is active‐high. The default value of the rden_polarity_sel parameter is
1’b1.
en_rd_when_empty
The en_rd_when_empty parameter allows the FIFO to be read when the empty flag is
asserted. When en_rd_when_empty is set to 1’b0, read operations are not allowed when the
empty flag is asserted. If the user tries to read the FIFO while the en_rd_when_empty
parameter is set to 1’b0, the read_error signal will be asserted on the following clock cycle and
the read operation will not occur. When en_rd_when_empty is set to 1’b1, read operations
may be performed when the empty flag is asserted. If the user reads the FIFO while the
en_rd_when_empty parameter is set to 1’b1, the read operation will occur and the read
pointer will be incremented. The user should disregard the level of the read_error if the
en_rd_when_empty parameter is set to 1’b1. The default value of the en_rd_when_empty
parameter is 1’b0.
en_wr_when_full
The en_wr_when_full parameter allows the FIFO to be written when the full flag is asserted.
When en_wr_when_full is set to 1’b0, write operations are not allowed when the full flag is
asserted. If the user tries to write the FIFO while the en_wr_when_full parameter is set to
1’b0, the write_error signal will be asserted on the following clock cycle and the write
operation will not occur. When en_wr_when_full is set to 1’b1, write operations may be
performed when the full flag is asserted. If the user writes the FIFO while en_wr_when_full
parameter is set to 1’b1, the write operation will occur and the write pointer will be
incremented. The user should disregard the level of the write_error if the en_wr_when_full
parameter is set to 1’b1. The default value of the en_wr_when_full parameter is 1’b0.