MPC8280 datasheet(1105/1386 Pages) FREESCALE

1105 / 1386 page

ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-45

The external framer then places the signaling information at the appropriate position in the super

frame. See Section 32.4.6, “Channel Associated Signaling (CAS) Support.”

•

Simple external logic is needed to synchronize the MCC-to-framer serial connection. When going

from TDM-to-ATM, the CAS information should be read by the MCC on the 24th frame of a super

frame.

•

The adaptive rate FIFO method can be implemented by the core by calculating the difference

between the ATM and MCC pointers.

•

When going from TDM-to-ATM, the ATM channel should be programmed to work at a higher rate

than the MCC super-channel rate. We expect that the jitter caused by the APC traffic reshaping will

depend on the ATM channel rate (PCR, PCR_FRACTION). Figure 32-32 illustrates this timing

issue. See also Section 32.4.1.2, “TDM-to-ATM.”

Figure 32-32. TDM-to-ATM Timing Issue

MCC timing:

BDs are ready to be transmitted at the rate shown below.

ATM timing:

The optimal ATM channel rate would match the MCC super channel rate exactly.

ATM timing (adjusted to higher rate):

If PCR and PCR_FACTION cannot provide the exact MCC super channel rate, the

ATM channel should be programmed to a higher rate to avoid the MCC buffer-not-ready

state. It is recommended that the ATM rate be double that of the MCC.

Extra request at the higher rate to compensate for jitter.

Note that some of the extra requests will not be needed (buffer-not-ready) and will

be ignored by the ATM controller.

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