GTS Ethernet Intel® FPGA Hard IP User Guide

ID 817676
Date 4/01/2024
Public

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4.3.3.1. TX PAUSE and TX PFC Ports

The i_tx_pause and i_tx_pfc[7:0] ports are used to request the TX MAC transmit PAUSE and Priority Flow Control packets to the remote link partner.

Figure 33. The i_tx_pause or i_tx_pfc to Request Transmission of a Control Frame

From the above waveform, i_tx_pause or i_tx_pfc[n] are the PAUSE/PFC request ports. Each operates independently. The i_tx_pause requests PAUSE frames for queue [n], while i_tx_pfc[n] requests PFC frames. You can assert the ports in any combination, but make sure the official Ethernet standard forbids utilizing PAUSE and PFC together on the same link. The packet completion illustrates what happens when a PAUSE or PFC request arrives in the core of the TX MAC while a packet is being handled. Due to the pipelines and FIFOs that connect the fabric to the hard Ethernet core, there is considerable latency between when a request is made and when it is processed. When a packet is in flight, the TX MAC waits for it to complete before proceeding.

The time when an XOFF frame is transmitted due to the request is shown by XOFF sent. When the XOFF frame is transmitted, a holdoff counter is started and programmed to one of the holdoff values. If the request is still high when the holdoff counter reaches 0, a new XOFF packet is sent. This continues until the request is deasserted, at which point an XON request is transmitted to the remote link partner.