Achronix ACE Version 5.0 - Manual (Page 83)

Editors Chapter 3. Concepts
Almost Full Offset
(decimal)
This defines the word depth at which the FIFO almost full signal
is asserted. The almost full flag is asserted when there are
(afull offset + 1) or fewer locations available to be written in the
FIFO. The
almost full signal is asserted when the the difference
between the Write Pointer and the Read Pointer is greater than or
equal to the difference between the Maximum FIFO Depth and the
value of this field (afull offset parameter).
Almost Empty
Offset (decimal)
This defines the word depth at which the FIFO almost empty
signal is asserted. The almost empty flag is asserted when there
are (aempty offset - 1) or fewer words remaining in the FIFO. The
almost empty signal is asserted when the the difference between
the Write Pointer and the Read Pointer is less than the value of this
field (aempty offset parameter).
First Word Fall Through Enabled When enabled, the first value written into the FIFO appears at the
dout output without having to perform a read operation. If First
Word Fall Through is disabled, the first data word written into the
FIFO is available at the FIFO output one
rdclk clock cycle after the
first read operation. This parameter only affects the availability of
the first word written into the FIFO after an empty condition.
Operation of the two modes is the same after the first read operation
is performed.
Synchronized Reset Mode When this is disabled, both the read and write pointers resets utilize
the Reset Synchronizer circuitry. When this option is enabled the
rstn input must be synchronous to the wrclk / rdclk clock
driving the FIFO.
Prevent Overflow/Underflow Enabling this option allows the user to read from the FIFO when the
FIFO is empty and write to the FIFO when it is full. Disabling this
safety check will allow the FIFO to run faster. Details can be found
in the user macro guide.
71 http://www.achronix.com UG001 Rev. 5.0 - 5th December 2012