VSC7440 datasheet(254/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

237

Figure 74 •

DTI Frame/Delay Sequence Using Inject Forever

3.25.3.5 Burst Size Test Using DTI Concatenation

Two (or more) DTIs can be concatenated, such that when one DTI completes, another DTI is activated.

This is depicted in the following illustration. It can be used for leaky bucket burst size testing, where the

first part of the sequence empties the bucket, followed by a steady frame flow with the rate of the leaky

bucket.

Note that when DTI concatenation is used, the last delay entry in the frame-delay sequence of the first

DTI is not awaited before starting the next DTI. That is, the next DTI is started when the first DTI reads an

entry with NEXT_PTR = 0. As shown in the illustration, the delay between the last Frame A and the first

Frame B will not be 150 clock cycles, but instead approximately 12 clock cycles. If this is considered

problematic, it can be addressed by using an additional DTI with a sequence consisting only of two delay

entries. For example, DTI #2 could be inserted between DTI#1, and DTI#3 and DTI#2 could then be

configured with a sequence consisting of two delay entries, with the first having delay = 150.

Figure 75 •

DTI Concatenation

DTI

Frame A

INJ_CNT=2

Delay

DELAY=100

FIRST_PTR

Frame B

INJ_CNT=1

Delay

DELAY=150

150

100

Time

Frame B

Resulting frame sequence:

150

Frame B

...

Inject forever

(In other words, until DTI is stopped)

100

Delay

DELAY=200

200

NEXT_PTR

Frame A

INJ_CNT=1

Delay

DELAY=100

FIRST_PTR

Frame B

INJ_CNT=1

Delay

DELAY=150

150

Time

Frame B

Frame A

Resulting frame sequence:

150

Frame B

...

100

NEXT_PTR=0

DTI #1

MODE=2

CNT=3

DTI_NEXT=3

DTI #3

MODE=0

CNT=10

FIRST_PTR

100

Frame A

Frame B is injected 10 times

NEXT_PTR=0

DTI #3 is enabled

when DTI #1

completes

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