- Programmable full (
prog_full
) indicates that the FIFO has reached a user-defined full threshold. - Programmable empty (
prog_empty
) indicates that the FIFO has reached a user-defined empty threshold.
For these thresholds, you can set a constant value or choose to have dedicated input ports, enabling the thresholds to change dynamically in circuit. Hysteresis is also optionally supported, by providing unique assert and negate values for each flag. Detailed information about these options are provided below.
Programmable Full
prog_full
) is asserted when the number of entries in the FIFO is
greater than or equal to the user-defined threshold. When the programmable full flag
is asserted, the FIFO can continue to be written to until the full flag (full
) is asserted. If the number of words in the FIFO
is less than the threshold, the flag is deasserted. The following figure shows the programmable full flag. You can write the FIFO
until there are seven words in the FIFO. Because the programmable full threshold is
set to seven, the FIFO asserts prog_full
after
seven words are written into the FIFO.
Programmable Full Threshold Range Restrictions
The programmable full threshold ranges depend on several features that dictate the way the FIFO is implemented, and include the following features:
- FIFO Implementation Type (Common or Independent Clock FIFOs)
- Symmetric or Non-symmetric Port Aspect Ratio
- Read Mode (Standard or First-Word-Fall-Through)
Programmable Empty
prog_empty
) is asserted when the number of entries in the FIFO is less
than or equal to the user-defined threshold. If the number of words in the FIFO is
greater than the threshold, the flag is deasserted.The following figure shows the programmable empty flag. You can write to the
FIFO until there are five words in the FIFO. Because the programmable empty
threshold is set to four, prog_empty
is asserted
until more than four words are present in the FIFO. After five words (or more) are
present in the FIFO, prog_empty
is deasserted.
Programmable Empty Threshold Range Restrictions
- FIFO Implementation Type (Common or Independent Clock FIFOs)
- Symmetric or Non-symmetric Port Aspect Ratio
- Read Mode (Standard or First-Word-Fall-Through)