MPC8280 datasheet(1079/1386 Pages) FREESCALE

1079 / 1386 page

ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-19

Figure 32-17. Pre-Overrun 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:

The MCC reads the data slower than

the ATM fills it. The ATM points to the

CESAC=4

MCC_Start=3, MCC_Stop=1

BD 6

BD 7

ATM_Start=5, ATM_Stop=7-1=6

ATM Rx pointer

BD table

last BD in the common BD table.

Step 4:

The ATM wraps around, and CESAC

reaches the ATM_Stop threshold. The

ATM write pointer freezes on the

current BD.

The MCC continues to process the

valid data. When the CESAC falls to the

ATM_Start threshold, the ATM advances

BD 1

BD 2

BD 3

BD 4

BD 5

MCC Tx pointer

ATM-to-TDM

BD 6

BD 7

ATM_Start

ATM Rx pointer

BD table

CESAC=6

to the first BD after EOSF.

Step 5:

After CESAC reaches the ATM_Start

threshold and the ATM advances to the

BD after EOSF, the ATM resynchronizes

and starts to receive valid data using

the new BD (start of SF).

MPC8280 Datasheet(PDF) 1079 Page - Freescale Semiconductor, Inc

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