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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

213

table. The table provides a specific egress port and QoS class to use in congestion control. The table is

accessed through the QFWD::FRAME_COPY_CFG register.

The following illustration shows the translation of transmit requests.

Figure 54 •

Translation of Transmit Requests

The CPUQ field instructs which of the eight CPU extraction queues should get a copy of this frame. Each

queue in the queue system is translated into either one of the two internal CPU ports or to a front port.

The egress QoS class can be set to the same value as the ingress QoS class or to a specific value per

CPU extraction queue. A super priority can also be used. For more information, see Super Priorities,

page 229.

The mirror field is the mirror probe number, which is set by the analyzer if the frame must be mirrored.

There are three mirror probes available, and for each of the probes, associated egress port and egress

QoS class can be set by the translation table.

Finally, if the learn-all field is set, the frame should also be forwarded to the stacking links. It is selectable

to forward the frame to either of the two stacking links or to both, depending on the stacking topology.

The following table lists the configuration registers associated with the forwarding function.

3.24.4

Congestion Control

The buffer control can only guarantee that no ingress port consumes more than a certain amount of

memory. Discards made by the buffer control are tail drops. The congestion control is more advanced in

that it facilitates intelligent discard where only frames belonging to a congested flow are discarded.

If the forwarder finds that some frame copies are made to a congested flow, it discards the copies (drop-

mode frames) or lets the copies block further processing of the ingress queue (flow control ports).

Table 142 •

Frame Forwarder Registers Overview

Description

Replication

QFWD::SWITCH_PORT_MODE Enables forwarding to/from port.

Forwarding speed configuration.

Drop mode setting.

Per port

QFWD::FRAME_COPY_CFG

Translates CPUQ/mirror/learn all to enqueuing requests.

QFWD::FRAME_COPY_LRNA

Learn All frame copy extra port.

None

QFWD::CPUQ_DISCARD

Disables enqueuing to specific CPU queues.

None

QSYS::FWD_PRESSURE

Configures forwarding pressure limits per port.

Per port

QFWD::MIRROR_CFG

Configures whether discarded copies should still generate a mirror

copy.

None

Translate

requests to

egress ports

Egress ports from destination set

CPU queues

Mirror request

LearnAll request

Egress ports

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