Low Latency 40G Ethernet Intel® FPGA IP User Guide: Agilex™ 5 FPGAs and SoCs

ID 813652
Date 4/01/2024
Public
Document Table of Contents

4.5.2. XON/XOFF Pause Frames

The sender transmits a PFC frame with the specified PFC pause quanta value when it receives an XOFF request. If an enabled priority queue is in the XOFF condition, a new PFC frame is transmitted after the minimum time gap. You specify the minimum time gap in the per priority queue TX Flow Control Signal XOFF Request Hold Quanta register. The minimum time gap between two consecutive PFC frames is 1 pause quanta or 512-bit times. PFC frame transmission ends when none of the PFC interfaces of all enabled priority queues is requesting PFC frames.

A transition from XOFF to XON in any enabled priority queue triggers the IP to transmit a PFC frame with pause quanta of 0 for the associated priority queue. The IP sends a single XON flow control frame. In the rare case that the XON frame is lost or corrupted, the remote partner should still be able to resume transmission. The remote partner resumes transmission after the duration specified in the previous XOFF flow control frame expires.