VSC7440 datasheet(236/444 Pages) MICROSEMI

236 / 444 page

Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

219

3.24.4.6 Frame Forwarder Monitoring

The performance of the frame forwarder can be monitored through the registers listed in the following

table.

3.24.5

Queue Mapping

When a frame is forwarded to an egress port, a frame reference is inserted into one of the port’s egress

queues. The egress queues are read by a programmable scheduler consisting of a number of scheduler

elements (SEs). Each SE serves 8 or 16 queues, configurable through the HSCH::HSCH_LARGE_ENA

registers. Each SE selects the next input to transmit and forwards the decision to a next-layer SE,

selecting from which of its inputs to transmit. There are a total of three layers, with layer 0 being the

queue connected layer. Connections between the layers are fully configurable in HSCH::L0_CFG and

HSCH::L1_CFG. For more information about SE functionality, see Scheduling, page 225 and Bandwidth

Control, page 226.

The scheduler includes a dual leaky bucket shaper to limit the traffic rate from inputs attached to it. To

distribute the bandwidth between the inputs, the scheduler also contains a weighted round robin arbiter.

The number of queues available in total for all ports is 3,358. The queue mapper must be configured to

how these queues are assigned to each egress port. The overall traffic management for each port is the

result of the queue mapping and scheduler hierarchy.

The following illustration shows an example of the default egress port hierarchy. At layer 0, eight SEs

select between data in the same QoS level, with queues from each source port. This forms a basic traffic

manager, where all source ports are treated fair between each other, and higher priorities are preferred.

This is accomplished by having the layer 0 SEs select input in a round robin fashion, and the mid-layer

select strictly higher inputs before lower inputs. In general, all SEs can be configured to various polices

on how to select inputs.

QRES::RES_STAT_CUR (replicated

as RES_CFG)

Returns current value this threshold is being compared with.

QRES::WRED_PROFILE (72 profiles) Profile description. There are 3 (grp) × 3 (DP) × 8 (prio) profiles.

QRES::WRED_GROUP

WRED group membership configuration per port.

QRES::PFC_CFG

Enable PFC per port.

QRES::RES_QOS_MODE

Enable QoS reservation for QoS classes.

QFWD::SWITCH_PORT_MODE

Controls whether yellow traffic can use reserved space (YEL_RSVD). Allows

ports to use shared space (IGR_NO_SHARING, EGR_NO_SHARING).

Table 149 •

Frame Forwarder Monitoring Registers Overview

Description

QFWD::FWD_DROP_EVENTS

Sticky bits per port telling if drops from each individual ingress port

occurred.

QFWD::FWD_CPU_DROP_CNT

Counts number of frames not forwarded to the CPU due to congestion.

QFWD::FWD_STAT_CNT

Counts number of frame copies added to the egress queues in total.

QFWD::FWD_PRESS_DROP_CNT

Counts number of frame copies discarded due to forward pressure.

Value is the total discards across all ports.

QSYS::MMGT_IQ_STAT

Returns current ingress queue size.

QSYS::MMGT

Returns number of free references for the egress queues.

Table 148 •

Congestion Control Registers Overview (continued)

Description

VSC7440 Datasheet(PDF) 236 Page - Microsemi Corporation

VSC7440 Datasheet(HTML) 236 Page - Microsemi Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL