Achronix Speedster22i User Macro Guide - Manual (Page 182)

Memories LRAMFIFO
Speedster22i Macro Cell Library Achronix Semiconductor Proprietary PAGE 165
Table 6-56: Condition to Assert almost_full Flag based on afull_offset Parameter Assignment
Condition when
almost_full flag is asserted
Condition when almost_full flag is
deasserted
afull_offset or fewer empty loca-
tions remain in the FIFO. There are at least (afull_offset +1) empty
locations remaining in the FIFO.
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 performed without monitoring the empty flag. For example, if the
aempty_offset parameter is set to 7’h04 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 default value of the aempty_offset
parameter is 7’h04, corresponding to four or fewer words remaining in the FIFO.
Table 6-57: Condition to Assert almost_empty Flag based on aempty_offset Parameter Assignment
Condition when
almost_empty flag is
asserted
Condition when almost_empty flag is
deasserted
aempty_offset or fewer
words remain in the FIFO. There are at least (aempty_offset +1) words in
the FIFO.
Status Flags
Empty Flag
The Empty (empty) flag is asserted after the FIFO is reset or when all of the data has been read
from the FIFO. The Empty flag is synchronous to the rdclk clock domain. Further attempts to
read the FIFO when the Empty flag is asserted will be blocked, the Read Error (read_err) flag
will be set in the following rdclk clock cycle, and the Read Pointer will remain unchanged.
Almost Empty Flag
The Almost Empty (almost_empty) flag is asserted when there are aempty_offset or fewer
words remaining in the FIFO (See
Table 6‐57: Condition to Assert almost_empty Flag based
on aempty_offset Parameter Assignment ). The almost_empty flag may be used to determine
the number of blind reads from the FIFO that can be performed without monitoring the empty
flag. For example, if the aempty_offset parameter is set to 7’h04 and the almost_empty flag is
deasserted, 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 Almost Empty flag
is synchronous with the rdclk clock input.
Full Flag
The Full (full) flag is asserted when all of the available locations of the FIFO have been written.
It is synchronous to the wrclk clock domain. Further attempts to write the FIFO when the Full
flag is asserted will be blocked, the Write Error (write_err) flag will be set in the following
wrclk clock cycle, and the Write Pointer will remain unchanged.
Almost Full Flag
The Almost Full (almost_full) flag is asserted when there are afull_offset or fewer available
locations remaining in the FIFO. The almost_full flag may be used to determine the number