Motorola PowerQUICC II MPC8280 Series Reference Manual page 1053

Freescale Semiconductor, Inc.
ATM-to-TDM Interworking
31.9.6 CAS Support
For applications requiring channel-associated signaling (CAS), circuit emulation with CAS
requires additional core processing. External framers perform the CAS manipulation
through a serial or parallel interface.
When the MCC receives a multi-frame block, it generates an interrupt to the core. The core
reads the CAS block from the external framer and places it at the end of the ATM data
buffer after the structured multi-frame block. The core then passes the buffer pointer to the
ATM controller, and the controller packs the data and CAS block into AAL1 CES cells. All
AAL1 CES functions, such as generating PDU-headers and structured pointers, operate
normally.
When the ATM controller receives a multi-frame block, it generates an interrupt to the core.
The core reads the CAS block from the data buffer and writes it to the external framer. The
core then moves the buffer pointer to the MCC. The buffer's data length should not include
the CAS octets.
To optimize the process, the framer may interrupt the core only when the CAS information
changes. (CAS information changes slowly.) The core can keep the CAS block in memory
and connect to the framer only when the CAS changes. The core can use regular read and
write cycles when connecting to the framer through a parallel interface.
The MCC and ATM controller should be synchronized with the framer's multi-frame block
boundary. At the ATM side, the structured block size should equal the multi-frame block
size plus the size of the CAS block so that the structured pointer, inserted by the ATM
controller, points to the start of the structured data block. At the MCC side, the MCC must
to be synchronized with the super frame sync signal. This synchronization can be achieved
by external logic that triggers on the super frame sync signal and starts delivering the frame
sync to the MCC. When loss of super frame synchronization occurs, this logic should reset
and trigger again on the next super frame indication.
31.9.7 Trunk Condition
According to the Bellcore standard, the interworking function (IWF) should be able to
transmit special payload on both ATM and TDM channels to signal alarm conditions
(Bellcore TR-NWT-000170). The core can be used to generate the trunk condition payload
in special buffers (or existing buffers) for the ATM controller or MCC.
31.9.8 ATM-to-ATM Data Forwarding
Automatic data forwarding can be used to switch ATM AAL0 cells from one ATM port to
another without core intervention. The ATM receiver and transmitter should be programed
to process the same BD table. When the ATM receiver fills an AAL0 buffer, the ATM
transmitter sends it. The ATM receiver and transmitter are synchronized using the same
MOTOROLA Chapter 31. ATM Controller and AAL0, AAL1, and AAL5 31-39
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