MPC8280 datasheet(1073/1386 Pages) FREESCALE

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ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-13

Table 32-1 describes CAS routing table entry fields.

32.4.7.2

TDM-to-ATM CAS Support

During the segmentation process, the AAL1 CES transmitter reads the CAS data from the internal CAS

block and packs the data and the signaling information at the end of an AAL1 super frame (depicted in

Figure 32-3). All AAL1 functions operate normally (generating AAL1 PDU-headers, structured pointers,

etc.). Each common (MCC, ATM) BD table should point to buffers that can contain a whole number of

super frames. The last buffer of the super frame is marked as the end of a super frame (BD[EOSF]=1).

After closing a buffer with the EOSF indication, the ATM transmitter processes the CAS data—reads it

from the internal CAS block and inserts it into the cell payload at the transmit side. The EOSF indication

in the BD is statically set by the CPU when initializing the BD table.

Figure 32-12. CAS Flow TDM-to-ATM

The CAS block is automatically written to internal RAM by the MCC receiver using a separate TDM.

When a super frame is received the MCC should be triggered with a super-frame (multi-frame) SYNC

from the external framer. The incoming CAS block should be captured by the MCC only once for each

super frame (on the last frame).

Table 32-1. CAS Routing Table Entry Field Descriptions

Bits

Name

Description

Wrap bit. When set, this bit indicates the last circular table entry. During initialization, the host must clear

all W bits in the table except the last one, which must be set.

—

Reserved, should be cleared during initialization.

F/S

First/Second.

0 Indicates that the signaling information occupies the first nibble in the CAS block (LSB).

1 Indicates that the signaling information occupies the second nibble in the CAS block (MSB).

3–7

SOP

Signaling Offset Pointer. Offset of the signaling nibble from the internal CAS base address.

Note that in ESF mode the maximum offset is 23 and in E1 framing format the maximum offset is 31.

EOSF

Buffer 1

Buffer 2

Buffer 3

Buffer 4

MCC

Data I/F

T1/E1 framer

MCC

Rx pointer

ATM

Tx pointer

ATM

UTOPIA

interface

BD table per VC

MCC

Incoming CAS block per trunk

(internal RAM)

Transmit

CAS routing

table

Super

frame

Super

frame

CAS serial I/F

T1/E1 framer

Shown in

Figure 1-10

Note: With CAS only 4 T1/E1 are supported.

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