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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

229

3.24.8

Queue System Initialization

The queue system automatically initializes all tables and data structures when setting

RAM_CTRL.RAM_ENA to 1, followed by setting RAM_CTRL.RAM_INIT to 1. Software should

afterwards wait for 150 µs or wait for the RAM_INIT bit to be cleared by hardware. After that the

RESET_CFG.CORE_ENA must be raised, and the queue system is ready to operate. All thresholds and

queue mappings are prepared with operational values. Configuration can afterwards be modified. The

only per-port setting required to change in the queue system for initial bring-up of the queue system is

the SWITCH_PORT_MODE.PORT_ENA, which must be set to one allowing switching of frames to and

from the port.

3.24.9

Miscellaneous Features

This section provides information about other miscellaneous features of the queue system.

3.24.9.1 Frame Aging

The queue system supports discarding of frames pending in the queue system for too long time. This is

known as frame aging. The frame aging period is configured in FRM_AGING.MAX_AGE, which controls

the generation of a periodical aging tick.

The packet memory manager marks frames pending in the queue system when the aging tick occurs.

Frames pending for more than two aging ticks are subject to frame aging and are discarded by the queue

system when scheduled for transmission. As a consequence, frames can be discarded after pending

between one or two aging periods in the queue system.

The following table lists the configuration registers associated with frame aging.

3.24.9.2 Super Priorities

There are two special queues available in each egress port: super priority queue 0 and super priority

queue 1. For more information, see Figure 61, page 220. These queues are selected before any other

queues. They are intended for urgent protocol traffic injected by the CPU system. Frames in super

priority queue 0 disregard the output shaper state and are not counted in the shaper’s buckets. Frames in

super priority queue 1 obey the output shaper state and are counted in the shaper’s buckets.

The following frames can be added to the super priority queues:

•

AFI injected frames: The AFI can be configured to inject into either of the super priority queues. For

more information, see Adding Injection Frame, page 244.

•

CPU injected frames: Frames injected with an IFH with the SP flag set are inserted into the super

priority queue as being set in the drop precedence (DP) IFH field.

•

CPU extracted, mirror, learn all frames: Frames subject to the translation in

QFWD::FRAME_COPY_CFG can configure use of either of the super priority queues.

3.24.9.3 Frame Modifications in the Queue System

The queue system typically passes data completely untouched from the ingress to the egress side,

except for a few special cases.

Frame copies to the CPU can be sent into the rewriter with two different priority schemes, involving

modification of the internal frame header. Either the frame takes the QoS class from the CPU extraction

queue number or it takes the QoS class from the configuration in QFWD::FRAME_COPY_CFG. This is

controlled in PORT_MODE.CPU_PRIO_MODE.

Table 156 •

Frame Aging Registers Overview

Field

Description

Replication

QSYS::FRM_AGING.MAX_AGE

Sets the aging period

None

HSCH::PORT_MODE.AGE_DIS

Disables aging checks per egress port

Per port

HSCH::PORT_MODE.FLUSH_ENA

Regards various frames as being too oldNone

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