MPC8280 datasheet(1160/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

34-14

Freescale Semiconductor

Figure 34-9. Transmit Queue Behavior: Link Clock Rate Faster than TRL, Worst-Case Event Sequence

34.3.2.4

Differences in CTC Operation

Overall, CTC operation is similar to ITC operation in task partitioning and overall structure. Differences

are as follows:

1. Transmit buffers are still maintained for the non-TRL links, but these buffers will not ‘jitter’, since

the transmit clocks are all the same. However, queue depths may vary slightly because PHY

requests, while synchronous, will not necessarily come in simultaneously (i.e. may have constant

offsets) and will definitely not be serviced simultaneously.

Queue extraction pointer

Tx Queue

(Transmitted by non-TRL task)

Normal ‘Wander zone’

Queue extraction pointer

Tx Queue

Before stuff event can

(Transmitted by non-TRL task)

Normal ‘Wander zone’

TRL stuff event occurs

a cell during a round

robin pass.

Depth decreases to 2.x

and this link is not given

“imminent stuff” flagged

happen, queue depth

creeps down below 2.x

threshold to 1.x

Queue extraction pointer

Tx Queue

(Transmitted by non-TRL task)

Normal ‘Wander zone’

Stuff event occurs,

bringing queue depth

back to 2.x

“imminent stuff’

remains flagged, but

is held off for minimum

5 frames.

Queue extraction pointer

Tx Queue

Holdoff expires and

(Transmitted by non-TRL task)

Normal ‘Wander zone’

stuff event occurs,

bringing queue depth

back to normal depth

of 3.x

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