VSC7440 datasheet(252/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

235

Miscellaneous DTI related parameters are shown in the following table.

Frame entries in a DTI sequence may point to the same frame in the queue system’s buffer memory. For

example, shown in the following illustration, frame A and frame B shown may point to the same frame in

the buffer memory.

The delay entries in a DTI sequence must be configured such that they are longer than the transmission

time (given the port speed) of the preceding frame in the sequence.

If a DTI sequence is configured with two consecutive frame entries, then these will be injected with a

minimum delay of approximately 14 clock cycles.

3.25.3.1 Frame-Delay Sequence

A DTI flow typically consists of a sequence of alternating frame/delay entries in the frame table. If a given

frame is to be injected multiple times (FRM_ENTRY_PART0.INJ_CNT>1), then the delay of the following

entry in the sequence is applied after each injection. If additional delay is required after the last injection,

then this can be achieved by an additional delay entry. The use of delay entries is shown in the following

illustration.

Figure 71 •

DTI Frame/Delay Sequence Example

3.25.3.2 Bandwidth Fine Tuning

The combination of INJ_CNT and two following delay entries can be used to fine tune the rate generated

by a DTI flow. This is shown in the following illustration, where a small delay after the four injections of

frame A is used to fine tune the rate of the DTI flow.

Table 163 •

Miscellaneous DTI Parameters

Field

Description

Replication

DTI_CTRL

Bandwidth of DTI flow

0: <5 Gbps

1: >=5 Gbps

Per DTI

DTI_CTRL

ENA

Enables DTI

Per DTI

DTI

Frame A

INJ_CNT=2

Delay

DELAY=150

FIRST_PTR

Frame B

INJ_CNT=2

Delay

DELAY=100

Delay

DELAY=200

Frame C

INJ_CNT=1

Delay

DELAY=125

150

100

100 + 200 = 300

125

Time

Frame A

Frame B

Frame C

Frame A

Resulting frame sequence:

150

Frame A

...

Inserted after each

injection of Frame B.

Inserted after last injection of

Frame B.

NEXT_PTR=0

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