The MRMAC AXI4-Stream provides support for the sending and receiving of Preemption packets (mPackets) as defined in Clause 99 of IEEE Standard for Ethernet (IEEE Std 802.3-2018). Preemption capabilities include outbound preemption header insertion, outbound packet preemption (including mFCS calculation and insertion), inbound preemption header extraction, and inbound preempted packet integrity checking.
The user logic is required to handle all other aspects of the preemption protocol, including auto-negotiation of the preemption feature with the link partner and received packet fragment reassembly.
Preemption capability is available on a per-port basis and is enabled by
setting the ctl_preempt_enable_<N> field of the port’s
MODE_REG register. Preemption should only be enabled if it is determined that the link partner
supports the preemption capability.