VSC7440 datasheet(292/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

275

are received from the queue system with an era value eligible for aging. Frames discarded by aging are

counted in DSM::AGED_FRMS.AGED_FRMS_CNT.

3.27.6

Setting Up Transmit Data Rate Limiting

The disassembler can limit the transmit data rate as specified in IEEE802.3ar, which defines the

following three rate limiting methods. The disassembler allows enabling of any combination of the

following three methods.

•

Frame overhead

•

Payload data rate

•Frame rate

The following table lists the registers associated with rating limiting.

If more than one of the rate limiting modes previously mentioned are enabled, the additional inter-packet

gap is the maximum of each of the values generated by one of the enabled modes. However, if only the

frame overhead and the data payload data rate modes are enabled, the additional inter-packet gap can

be calculated as the sum of the additional gaps retrieved from each of the two modes. To enable the

function, set DSM::TX_RATE_LIMIT_MODE.TX_RATE_LIMIT_ACCUM_MODE_ENA to 1.

If the preamble of a frame is not to be counted as payload, set

DSM::TX_RATE_LIMIT_MODE.PAYLOAD_CFG to 0.

In addition, if parts of the frame are to be seen as header and not counted as payload, set

DSM::TX_RATE_LIMIT_MODE.PAYLOAD_CFG to 1.

DSM::TX_RATE_LIMIT_HDR_CFG.TX_RATE_LIMIT_HDR_SIZE defines how much of the frame that

should be considered as header. Note that this register is global for all ports enabled by

DSM::TX_RATE_LIMIT_MODE.PAYLOAD_CFG. The payload configuration applies to Payload Data

Rate and Frame Rate mode.

Table 199 •

Aging Configuration Register Overview

Target::Register.Field

Description

Replication

DSM::BUF_CFG.AGING_ENA

Enable aging of frames stuck in the disassembler buffer system for

long periods.

Per port

Table 200 •

Aging Status Register Overview

Target::Register.Field

Description

Replication

DSM::AGED_FRMS.AGED_FRMS_CNT

Count number of aged frames.

Per port

Table 201 •

Rate Limiting Common Configuration Registers Overview

Target::Register.Field

Description

Replication

DSM::TX_RATE_LIMIT_MODE.

TX_RATE_LIMIT_ACCUM_MODE_ENA

Enables for accumulated rate limit mode.

Per port

DSM::TX_RATE_LIMIT_MODE.

PAYLOAD_PREAM_CFG

Defines whether the preamble is counted as payload in

txRateLimitPayloadRate and txRateLimitFrameRate mode.

Per port

DSM::TX_RATE_LIMIT_MODE.

PAYLOAD_CFG

Defines if what is configured as header size in

TX_RATE_LIMIT_HDR_SIZE::

TX_RATE_LIMIT_HDR_CFG is subtracted form the

payload.

Per port

DSM::TX_RATE_LIMIT_MODE.

IPG_SCALE_VAL

Scales the IPG calculated by txRateLimitFrameOverhead

and/or txRateLimitPayloadRate by a power of 2.

Per port

DSM::TX_RATE_LIMIT_HDR_CFG.

TX_RATE_LIMIT_HDR_SIZE

Defines how much of the frame is seen as header and not

counted as payload.

per port

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