MPC8280 datasheet(1156/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

34-10

Freescale Semiconductor

Figure 34-5. IMA Transmit Task Interaction

34.3.2.1

TRL Operation

A request from the TRL PHY is used to trigger a complete round-robin process of cell scheduling and

distribution, distributing one cell for each of the transmit queues of the N links in the IMA group. For each

link, the microcode will:

1. Determine whether an ICP cell or a data/filler cell should be sent for the link:

— If data/filler, determine whether link is in ‘active’ or ‘filler-only’ mode

— If active, run the APC scheduling algorithm to find the next scheduled ATM channel

2. Distribute either:

— An ICP cell

— A filler cell (if ‘filler-only’ or ‘active’ with nothing scheduled in the APC)

— A data cell (if a channel is scheduled in the APC, performing the appropriate segmentation task

for the scheduled ATM channel, as determined by the channel’s AAL type)

The cells are distributed by writing the complete cells into circular transmit queues provided per link.

These transmit queues function as ‘jitter buffers’, as they are used to decouple the transmit rate of the TRL

PHY from the transmit rate of the non-TRL PHYs in the group to allow for clocking differences between

the PHYs.

APC

Jitter

Tx Queue

Buffers

Tx Queue

TRL Tx Task

non-TRL Tx

UTOPIA Multi-PHY

Task

SAR

N times

TRL Tx

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