FPGA.GR.Low Latency FIFO Read Operation

For Lower Latency FIFO Reads, choose First Word Fall Through Read Mode.

The FIFO Generator core supports two modes of read options, standard read operation and first-word fall-through (FWFT) read operation. The standard read operation provides the user data on the cycle after it was requested. The FWFT read operation provides the user data on the same cycle in which it is requested. For low latency, using the FWFT operation can save 1-2 clock cycles.Below is a comparison when selecting Read Mode in FIFO Generator

When selecting "Standard FIFO" Read mode, "Read Latency" is 1 in this case.

When selecting "First Word Fall Through" Read mode, "Read Latency" is 0 in this case.

Operation of each mode has different behavior, therefore care must be taken to handle each case.

Below is the timing diagram for Standard Read Operation. As you can see the data is valid one clock after the rd_en signal is asserted.

Below is the timing diagram for FWFT. The data is valid before the rd_en is asserted reducing latency compared to Standard Read Operation above.