KSZ8852HLE Datasheet, PDF (41/190 Pages) Micrel Semiconductor – Two-Port 10/100 Mb/s Ethernet Switch with 8 or 16-Bit Host Interface

Micrel, Inc.
Table 6. FID + SA Lookup in VLAN Mode
FID+SA Found in
Dynamic MAC Table?
Action
No
Learn and add FID+SA to the Dynamic MAC Address Table
Yes
Update time stamp
KSZ8852HLE
QoS Priority Support
The KSZ8852 provides quality-of-service (QoS) for applications such as VoIP and video conferencing. The KSZ8852 offer
1, 2, and 4 priority queues option per port. This is controlled by bit[0] and bit[8] in P1CR1, P2CR1 and P3CR1 registers as
shown below:
• Bit[0], Bit[8] = ‘00’ Egress port is a single output queue as default.
• Bit[0], Bit[8] = ‘01’ Egress port can be split into two priority transmit queues. (Q0 and Q1)
• Bit[0], Bit[8] = ‘10’ Egress port can be split into four priority transmit queues. (Q0, Q1, Q2 and Q3)
The four priority transmit queues is a new feature in the KSZ8852. Queue 3 is the highest priority queue and Queue 0 is
the lowest priority queue. If a port's transmit queue is not split, high priority and low priority packets have equal priority in
the transmit queue.
There is an additional option for every port via bits[15,7] in the P1ITXQRCR1, P1TXQRCR2, P2TXQRCR1, P2TXQRCR2,
P3TXQRCR1, and P3TXQRCR2 Registers to select either always to deliver high priority packets first or use weighted fair
queuing for the four priority queues scale by 8:4:2:1.
Port-Based Priority
With port-based priority, each ingress port is individually classified as a specific priority level. All packets received at the
high-priority receiving port are marked as high priority and are sent to the high-priority transmit queue if the corresponding
transmit queue is split. Bits[4:3] of registers P1CR1, P2CR1, and P3CR1 is used to enable port-based priority for Ports 1,
2, and the host port, respectively.
802.1p-Based Priority
For 802.1p−based priority, the KSZ8852 examines the ingress (incoming) packets to determine whether they are tagged.
If tagged, the 3−bit priority field in the VLAN tag is retrieved and used to look up the “priority mapping” value, as specified
by the register SGCR6. The “priority mapping” value is programmable.
Figure 8 illustrates how the 802.1p priority field is embedded in the 802.1Q VLAN tag.
August 31, 2015
Figure 8. 802.1p Priority Field Format
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