Freescale Semiconductor MPC8260 Figure 31-16. Pre-Underrun Sequence

ATM AAL1 Circuit Emulation Service
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
31-18 Freescale Semiconductor
Figure 31-16. Pre-Underrun Sequence
BD 1
BD 2
BD 3
BD 4
BD 5
MCC Tx pointer 0
0
0
0
0
ATM- t o- T D M
Step 1:
Initialize the MCC and ATM pointers
to the same BD table.
CESAC=0
MCC_Start=3, MCC_Stop=1
BD 6
0
BD 7
0ATM_Start=5, ATM_Stop=7-1=6
MCC_Start
ATM Rx pointer
BD table
W
BD 1
BD 2
BD 3
BD 4
BD 5
MCC Tx pointer 1
1
1
0
0
ATM- t o- T D M
Step 2:
When CESAC reaches MCC_Start,
the MCC starts transmitting.
CESAC=3
MCC_Start=3, MCC_Stop=1
BD 6
0
BD 7
0ATM_Start=5, ATM_Stop=7-1=6
MCC_Start
ATM Rx pointer
BD table
W
BD 1
BD 2
BD 3
BD 4
BD 5
MCC Tx pointer
0
0
0
0
1
ATM- t o- T D M Step 3:
Because the MCC is reading the data
faster than the ATM, CESAC falls to the
CESAC=1
MCC_Start=3, MCC_Stop=1BD 6
0
BD 7
0ATM_Start=5, ATM_Stop=7-1=6 MCC_Start
ATM Rx pointer
BD table
W
MCC_Stop threshold. The MCC pointer
then freezes, and the current buffer1 is
retransmitted for a multiple of the frame
size. (The buffer size should be a multiple
of the frame size.)
The MCC can optionally transmit
the underrun template.
1
Step 4:
The MCC switches to pre-underrun
state and continues to send the current
buffer (the last buffer that was sent).
When CESAC reaches MCC_Start and
a multiple of complete frames has been
sent, the MCC starts to transmit again
(returns to Step 2 in this flow).