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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

126

3.11.6

Advanced Resource Management

A number of additional handles into the resource management system are available for special use of

the device. They are described in the following table.

3.11.7

Ingress Pause Request Generation

During resource depletion, the shared queue system either discards frames when the ingress port

operates in drop mode, or holds back frames when the ingress port operates in flow control mode. The

following describes special configuration for the flow control mode.

The shared queue system is enabled for holding back frames during resource depletion in

SYS:PORT:PAUSE_CFG.PAUSE_ENA. In addition, this enables the generation of pause requests to the

port module based on memory consumptions. The MAC uses the pause request to generate pause

frames or create back pressure collisions to halt the link partner. This is done according to the MAC

configuration. For more information about MAC configuration, see MAC, page 17.

The shared queue system generates the pause request based on the ingress port’s memory

consumption and also based on the total memory consumption in the shared queue system. This

enables a larger burst capacity for a port operating in flow control while not jeopardizing the non-dropping

flow control.

Generating the pause request partially depends on a memory consumption flag, TOT_PAUSE, which is

set and cleared under the following conditions:

•

The TOT_PAUSE flag is set when the total consumed memory in the shared queue system exceeds

the SYS:PORT:PAUSE_TOT_CFG.PAUSE_TOT_START watermark.

•

The TOT_PAUSE flag is cleared when the total consumed memory in the shared queue system is

below the SYS:PORT:PAUSE_TOT_CFG.PAUSE_TOT_STOP watermark.

The pause request is asserted when both of the following conditions are met.

Table 99 •

Resource Management

Description

Forced drop of egress and

ingress frames

QSYS::EGR_DROP_MODE

QSYS::SWITCH_PORT_MODE.INGRESS_DROP_MODE.

If either an ingress port or an egress port in a frame transfer are configured for drop

mode, congestion results in frame discards. Otherwise frames are held back in the

ingress queues with potential head-of-line blocking effects.

Normally all egress ports are set to non-drop-mode while the ingress drop mode

reflects whether or not the port is configured for flow control.

Prevent ingress port from

using of the shared

resources.

QSYS::IGR_NO_SHARING.

For frames received on ports set in this mask, the shared watermarks are

considered exceeded. This prevents the port from using more resources than

allowed by the reservation watermarks.

Prevent egress port from

using of the shared

resources.

QSYS::EGR_NO_SHARING.

For frames switched to ports set in this mask the shared watermarks are considered

exceeded. This prevents the port from using more resources than allowed by the

reservation watermarks.

Weighted Random Early

Detection (WRED)

QSYS::RED_PROFILE.

It is possible to discard frames with increasing probability as the consumption of

shared resources per QoS class per drop precedence level increases.

QSYS::RED_PROFILE

configures a low and a high watermark per QoS class per

drop precedence level. The probability of discarding a frame increases linearly from

0% when the consumption is at the low watermark to 100% when the consumption

exceeds the high watermark.

Prevent dequeuing

QSYS::PORT_MODE.DEQUEUE_DIS.

Each egress port can disable dequeuing of frames from the egress queues.

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