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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

34-15

2. The non-TRL tasks do not determine when to perform stuffing on the non-TRL links. When the

TRL flags ‘imminent stuff’ on its own link, it will flag ‘imminent stuff’ on all of the non-TRL links

as well. Thus, the non-TRL links will also stuff their links every 2048 cells.

3. The non-TRL queue depths are the same as the TRL’s queue (i.e. 4 cells).

34.3.3

Receive Architecture

The receive task consists of three parts. The first part is for cell reception from the link. The second part

provides the trigger for activating the cell processing task, including timing recovery if desired. The third

part performs the actual cell processing (i.e. passing cells to the ATM layer). The cell reception task

services requests from the links (via the UTOPIA multi-PHY interface and the FCC), maintains the link

state, and (if the link and group state dictates) writes the received cells into the link’s delay compensation

buffer in external memory. The cell processing activation function coordinates passing cells from the cell

reception task, on either an on-demand basis or at a rate determined by the reconstructed IDCR (IMA data

cell rate). The cell processing task extracts cells from the delay compensation buffers and passes them to

the ATM layer for processing.

Figure 34-10. IMA Receive Task Interaction

34.3.3.1

Cell Reception Task

In the cell reception task, received ICP cells in which an SCCI change is noted, except for the first ICP

received cell, are passed to a user-defined receive AAL0 channel to be processed by software. These

Cell Reception

UTOPIA Multi-PHY

Task

Delay

Compensation

Buffers

Cell Processing

Task

Cell Processing Activation Function

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