Freescale Semiconductor MPC8260 - Manual (Page 1114)

Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
33-12 Freescale Semiconductor
Figure 33-5. IMA Transmit Task Interaction
33.3.2.1 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 Tx Queue Tx Queue
TRL Tx Task
non-TRL Tx
UTOPIA Multi-PHY
Task
SAR
N times
TRL Tx