KSZ8842-16MBL-EVAL MICREL [Micrel Semiconductor], KSZ8842-16MBL-EVAL Datasheet - Page 46

• Manufacturer Part Number: KSZ8842-16MBL-EVAL
• Description: 2-Port Ethernet Switch with Non-PCI Interface
• Manufacturer: MICREL [Micrel Semiconductor]

QoS Priority Support
The KSZ8842M provides Quality of Service (QoS) for applications such as VoIP and video conferencing. Offering four
priority queues per port, the per-port transmit queue can be split into four priority queues: Queue 3 is the highest priority
queue and Queue 0 is the lowest priority queue. Bit 0 of registers P1CR1, P2CR1, and P3CR1 is used to enable split
transmit queues for ports 1, 2, and the host port, respectively.
Port-Based Priority
With port-based priority, each ingress port is individually classified as a high-priority receiving port. 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. Bit 4 and 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 KSZ8842M 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 compared against the “priority mapping” value, as
specified by the register SGCR6. The “priority mapping” value is programmable.
Figure 14 illustrates how the 802.1p priority field is embedded in the 802.1Q VLAN tag.
Micrel, Inc.
October 2007
FID+SA found in Dynamic
MAC Table?
No
Yes
DA found in
Static MAC
Table?
No
No
Yes
Yes
Yes
Yes
Use FID flag?
Don’t care
Don’t care
0
1
1
1
Action
Learn and add FID+SA to the Dynamic MAC Address Table
Update time stamp
Table 10. FID+DA Lookup in VLAN Mode
Table 11. FID+SA Lookup in VLAN Mode
Don’t care
FID match?
Don’t care
Don’t care
No
No
Yes
46
DA+FID found in
Dynamic MAC
Table?
No
Yes
Don’t care
No
Yes
Don’t care
Action
Broadcast to the membership ports
defined in the VLAN Table bits [18:16]
Send to the destination port defined in the
Dynamic MAC Address Table bits [53:52]
Send to the destination port(s) defined in
the Static MAC Address Table bits [50:48]
Broadcast to the membership ports
defined in the VLAN Table bits [18:16]
Send to the destination port defined in the
Dynamic MAC Address Table bits [53:52]
Send to the destination port(s) defined in
the Static MAC Address Table bits [50:48]
KSZ8842-16/32 MQL/MVL/MVLI/MBL
M9999-102207-1.9