AXI interface FIFOs are derived from the Native interface FIFO, as shown in the following figure. Three AXI interface styles are available: AXI4-Stream, AXI4, and AXI4-Lite. In addition to applications supported by the Native interface FIFO, AXI FIFOs can also be used in AXI System Bus and Point-to-Point high speed applications.
Use the AXI FIFOs in the same applications supported by the Native Interface FIFO when you need to connect to other AXI functions. AXI FIFOs can be integrated into a system by using the IP integrator. See the Vivado Design Suite User Guide: Designing IP Subsystems using IP Integrator (UG994) for more details.
The AXI interface protocol uses a two-way valid and ready
handshake mechanism. The information source uses the valid signal to
show when valid data or control information is available on the channel. The information
destination uses the ready signal to show when it can accept the data.
The following figures show an example timing diagram for write and read operations to
the AXI4-Stream FIFO, and an example timing diagram for write and
read operations to the AXI memory mapped interface FIFO.
The information source generates the valid signal to indicate when the data is
available. The destination generates the ready signal to indicate that
it can accept the data, and transfer occurs only when both the valid
and ready signals are High.
Because AXI FIFOs are derived from Native interface FIFOs, much of the behavior is common
between them. The ready signal is generated based on availability of
space in the FIFO and is held high to allow writes to the FIFO. The
ready signal is pulled Low only when there is no space in the FIFO
left to perform additional writes. The valid signal is generated based
on availability of data in the FIFO and is held High to allow reads to be performed from
the FIFO. The valid signal is pulled Low only when there is no data
available to be read from the FIFO. The information signals are mapped
to the din and dout bus of Native interface FIFOs. The
width of the AXI FIFO is determined by concatenating all of the
information signals of the AXI interface. The
information signals include all AXI signals except for the
valid and ready handshake signals.
AXI FIFOs operate only in First-Word Fall-Through mode. The First-Word Fall-Through (FWFT) feature provides the ability to look ahead to the next word available from the FIFO without issuing a read operation. When data is available in the FIFO, the first word falls through the FIFO and appears automatically on the output data bus.