Motorola PowerQUICC II MPC8280 Series Reference Manual page 1159

TBD_Base
Pointers
from ch 1
entry of
TCT
TBD_Offset
TBD_Base
Pointers
from ch 4
entry of
TCT
TBD_Offset
Figure 32-26. Transmit Buffers and BD Table Example
32.11.2 Receive Buffer Operation
The user prepares a table of BDs pointing to the receive buffers. The address of the first BD
is put in the channel's RCT[RBD_BASE]. When an ATM cell arrives, the CP opens the first
BD in the table and starts filling its associated buffer with received data. When the current
buffer is full, the CP increments RBD_OFFSET, which is the offset to the current BD from
RBD_BASE, and reads the next BD in the table. If the BD is empty (RxBD[E] = 1), the CP
continues receiving. If the BD is not empty, a busy condition has occurred and the ATM
receiver optionally issues an interrupt to the event queue.
Note that when the ATM receiver is in CES mode, the buffer-not-ready (busy) state is
handled by an automatic slip control mechanism; see Section 32.5, "ATM-to-TDM
Adaptive Slip Control."
MOTOROLA
Freescale Semiconductor, Inc.
BD memory space
Tx BD table
of ch 1
TxBD 1
TxBD 2
TxBD 3
TxBD 4
•
TxBD 5
•
TxBD 6
•
Tx BD table
of ch 4
TxBD 1
TxBD 2
TxBD 3
TxBD 4
•
•
TxBD 5
•
TxBD 6
TxBD 7
TxBD 8
TxBD 9
Chapter 32. ATM AAL1 Circuit Emulation Service
For More Information On This Product,
Go to: www.freescale.com
Buffer Descriptors
Data memory space
Tx buffer 1 of
channel 1
Tx buffer 3 of
channel 1
Tx buffer 4 of
channel 1
Tx buffer 1 of
channel 4
Tx buffer 2 of
channel 1
Tx buffer 2 of
channel 4
Tx buffer 3 of
channel 4
Tx buffer 8 of
channel 4
32-39