Data Sheet

Ethernet Controller I210 —Inline Functions
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7.2.7 Handling Time Sensitive Streams (802.1Qav)
7.2.7.1 Overview
The 802.1Qav is part of the AVB specifications that include Timing and Synchronization for time specific
applications (802.1AS), Stream Reservation (SR) protocol to guarantee the resources needed for
Audio/Video (AV) streams (802.1Qat), Forwarding and queuing enhancements for time sensitive
streams (802.1Qav).
802.1Qav provides a way to guarantee bounded latency and latency variation for time sensitive traffic
as AV. It specifies the priority usage and controlled bandwidth draining algorithms.
Note that when supporting Time Sensitive Streams, EEE should not be enabled (by the EEER register)
due to potential distortions of the time sensitive traffic scheduling.
7.2.7.2 I210 Transmit Modes
The I210 supports two transmit modes, legacy and Qav. The transmit mode is configured in
TQAVCTRL.QavMode register and must be set during the SW initialization cycle. The I210 transmit
mode cannot change during dynamic operation.
The I210 Legacy transmit is defined in Section 7.2. The rest of this sub chapter defines the I210
transmit functionality when configured to operate at Qav mode.
Note: When configured to Qav mode enabling the transmit short packet padding feature and
sending packets shorter than 64 bytes has some impact to the correctness of the credit
shaper arbitration as the arbitration is done based on the non padded transmit packet length.
7.2.7.3 Transmit Architecture in Qav Mode
To enable the proper priority and bandwidth allocation to the time sensitive streams the I210 transmit
architecture includes up to four transmit packet buffers, the transmit traffic is distributed between the
packet buffers based on the packet priority. The I210 software device driver directs the outgoing
packets to the relevant priority packet buffers by submitting them per priority to the proper descriptor
queues.
Legacy Qav
Packet Buffer Single transmit packet buffer Four transmit packet buffers
Queues
Four transmit queues
All enabled queues are associated to the single
transmit packet buffer
Four transmit queues
Each enabled queue is associated with a dedicated
transmit packet buffer
Data fetch arbitration Round robin between the queues
Combination of time based and most empty packet
buffer
Data transmit
arbitration
None - single packet buffer - first in first out
Combination of time based and credit shaper for the
SR queues and strict priority for the BE queues