Motorola PowerQUICC II MPC8280 Series Reference Manual page 1127

Possible interworking applications are as follows:
• Circuit emulation service (CES)
• Carrying voice over ATM
• Multiplexing low speed services, such as voice and data, onto one ATM connection
32.4.1 Automatic Data Forwarding
The basic concept of automatic data forwarding is to program the ATM controller and the
MCC to process the same BD table (ring).
The MCC and ATM receivers must be programmed to operate in opposite E-bit polarity.
That is, both receivers receive into buffers in which RxBD[E] = 0 and then set RxBD[E]
when the buffer is full. For the ATM receiver, set RCT[INVE] of the AAL1 CES-specific
areas of the receive connection table; see Section 32.9.1, "Receive Connection Table
(RCT)." For the MCC receiver, set CHAMR[EP].
32.4.1.1 ATM-to-TDM
When going from ATM to TDM (depicted in Figure 32-5), the ATM receiver reassembles
data received from a particular channel to a specific BD table. The MCC transmitter is
programmed to operate on the same table. When the ATM controller fills a receive buffer,
the MCC controller sends it. The controllers synchronize on the ATM controller's RxBD[E]
and the MCC's TxBD[R].
A threshold mechanism for the MCC transmitter is used to synchronize the automatic start
of the ATM-to-TDM data forwarding. The transmitter waits until the start threshold is
reached (enough cells are received) before sending the valid data. In effect, the MCC start
threshold mechanism implements a jitter buffer designed to accommodate the CDV of the
ATM network.
In a CES application, software should first initialize the MCC transmitter, then initialize the
ATM receiver. This way the MCC transmitter sends idle data (0xFF) until the ATM receiver
fills enough buffers to reach the MCC start threshold. (The receiver is effectively filling a
jitter buffer.) When the CES_Adaptive_Counter (CESAC) reaches the MCC_Start
threshold, the MCC super channel polling CESAC starts sending the received data with the
first frame SYNC. (The first octet using the first BD is sent on the first assigned time slot.)
Section 32.5, "ATM-to-TDM Adaptive Slip Control," shows the flow of ATM-to-TDM
interworking.
MOTOROLA
Freescale Semiconductor, Inc.
Chapter 32. ATM AAL1 Circuit Emulation Service
For More Information On This Product,
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Interworking Functions
32-7