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FIFOs

A FIFO is a first-in, first-out queue.

A FIFO typically has some internal storage limit (its capacity) but the interface is independent of that.

FIFOs are either synchronous or clock-domain crossing.

Synchronous FIFOs are either bubble-free (simultaneous read and write operations are always possible) or internally-pipelined (effect of a read or write is only visible at the opposite port a clock cycle later, also known as fully-registered).

Each of the two ports has a pair of handshake nets.

Some FIFOs provide further status output signals such as half or nearly full.

A FIFO can help achieve timing closure, but again the protocol must be transactional and a bubble-free FIFO cannot always be used owing to its combinational path(s), hence latency is introduced.