Freescale Semiconductor MPC8260 - Manual (Page 1118)

Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
33-16 Freescale Semiconductor
Figure 33-9. Transmit Queue Behavior: Link Clock Rate Faster than TRL, Worst-Case Event Sequence
33.3.2.4 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