The tx_client_fifo is built around a Dual Port
Inferred RAM, giving a total memory capacity of 4,096 bytes.
When a full frame has been written
into the transmit FIFO, the FIFO presents data to the MAC
transmitter. The MAC uses tx_axis_mac_tready to throttle the data
until it has control of the medium.
If the FIFO memory fills up, the
tx_axis_fifo_tready signal is used to halt the AXI4-Stream interface writing in data, until space becomes
available in the FIFO. If the FIFO memory fills up but no full frames are
available for transmission. For example, if a frame larger than 4,000 bytes
is written into the FIFO, the FIFO asserts the tx_overflow
signal and continues to accept the rest of the frame from you. The overflow
frame is dropped by the FIFO. This ensures that the AXI4-Stream FIFO interface does not lock up.