MPC8280 datasheet(1078/1386 Pages) FREESCALE

1078 / 1386 page

ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

32-18

Freescale Semiconductor

Figure 32-16. Pre-Underrun Sequence

BD 1

BD 2

BD 3

BD 4

BD 5

MCC Tx pointer

ATM-to-TDM

Step 1:

Initialize the MCC and ATM pointers

to the same BD table.

CESAC=0

MCC_Start=3, MCC_Stop=1

BD 6

BD 7

ATM_Start=5, ATM_Stop=7-1=6

MCC_Start

ATM Rx pointer

BD table

BD 1

BD 2

BD 3

BD 4

BD 5

MCC Tx pointer

ATM-to-TDM

Step 2:

When CESAC reaches MCC_Start,

the MCC starts transmitting.

CESAC=3

MCC_Start=3, MCC_Stop=1

BD 6

BD 7

ATM_Start=5, ATM_Stop=7-1=6

MCC_Start

ATM Rx pointer

BD table

BD 1

BD 2

BD 3

BD 4

BD 5

MCC Tx pointer

ATM-to-TDM

Step 3:

Because the MCC is reading the data

faster than the ATM, CESAC falls to the

CESAC=1

MCC_Start=3, MCC_Stop=1

BD 6

BD 7

ATM_Start=5, ATM_Stop=7-1=6

MCC_Start

ATM Rx pointer

BD table

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.

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).

MPC8280 Datasheet(PDF) 1078 Page - Freescale Semiconductor, Inc

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