Achronix Speedster22i User Macro Guide - Manual (Page 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 clock.
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 almost_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 flag 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 Maximum 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 Depth . The default value of the afull_offset parameter is 17’h00004, corre‐
sponding to five 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
almost_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 flag 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 value
assigned to the read_width parameter as shown in
Table 6‐19: FIFO read_width versus
Maximum Read Depth . The default value of the aempty_offset parameter is 17’h00004, corre‐
sponding to four or less words remaining in the FIFO.