Low latency self-timed flow-through FIFOs

Self-timed flow-through FIFOs are constructed easily using only a single C-element as control for each stage of the FIFO. Throughput can be very high in this type of FIFO as the communication required to send new data to the FIFO is local to only the first element of the FIFO. Circuit density can also be high because the control overhead is very small. However, because data must travel through every cell in the FIFO when moving from input to output, latencies can be long. This paper describes some alternative approaches to building self-timed flow-through FIFOs that reduce the latency while retaining the high throughput and relative simplicity of a flow-through design. Five designs are presented: a standard linear pow-through FIFO in which the data pass through every latch in the FIFO, a parallel FIFO in which data are delivered in turn to a set of parallel flow-through FIFOs, a tree FIFO in which data are fanned out into a tree of simple FIFOs, a square FIFO in which the tree is organized as a square array to achieve better layout packing, and a folded FIFO in which data will try to skip as many of the empty FIFO cells as possible to find the shortest path to the output.