Motorola PowerQUICC II MPC8280 Series Reference Manual page 1175

TCT
Fix=0
FirstQueue
The transmitter steps from one TxQD to the next along the queue links. The TCT[MaxStep]
parameter limits the number of TX Queues that the transmitter visits during a cell time. If
MaxStep is reached before the cell has been completely filled, one of the following events
takes place:
• TCT[ET]=0 (Timer CU disabled). The cell is padded with zeros and sent.
• TCT[ET]=1 (Timer CU enabled). If the timer has not expired, the cell is not sent.
(The transmitter attempts to fill the cell the next time this channel is scheduled.) If
the timer has expired, the cell is padded with zeros and sent
After the transmitter sends a cell, it saves the queue link of the last TxQD serviced in
TCT[FirstQueue].
33.3.2.2 Fixed Priority
In fixed priority mode (TCT[Fix]=1), the transmitter, with each new cell, starts with
searching the highest priority queue and then moves on to the lower priority queues. The
TCT[FirstQueue] points to the highest priority queue, as shown in Figure 33-5, and remains
unchanged by the CP.
MOTOROLA
Freescale Semiconductor, Inc.
Figure 33-4. Round Robin Priority
Chapter 33. ATM AAL2
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TxQD
NextQueue
TxQD
NextQueue
TxQD
NextQueue
AAL2 Transmitter
33-7