Freescale Semiconductor MPC8260 - Manual (Page 1119)

Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 33-17
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).
33.3.3 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 33-10. IMA Receive Task Interaction
33.3.3.1 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