MPC8280 datasheet(968/1386 Pages) FREESCALE

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ATM Controller and AAL0, AAL1, and AAL5

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

31-8

Freescale Semiconductor

The MPC8280 supports partially filled cells configured on a per-VC basis. In this mode (RCT[PFM] = 1),

the ATM controller copies only the valid octets from the cell user data field to the buffer.

31.2.2.2.1

AAL1 CES Receiver Overview

Refer to Section 32.3, “AAL1 CES Receiver Overview.”

31.2.2.3

AAL0 Receiver Overview

For AAL0, no specific adaptation layer processing is done. The ATM controller copies the whole cell to

an external buffer. Each buffer contains exactly one AAL0 cell. The ATM controller calculates and checks

the CRC10 of the cell payload and sets RxBD[CRE] if a CRC error occurs. AAL0 mode can be useful for

receiving OAM cells or AAL3/4 raw cells.

31.2.2.4

AAL2 Receiver Overview

Refer to Section 33.4.1, “Receiver Overview.”

31.2.3

Performance Monitoring

The ATM controller supports performance monitoring testing according to ITU I.610. When performance

monitoring is enabled, the ATM controller automatically generates and terminates FMCs (forward

monitoring cells) and BRCs (backward reporting cells). See Section 31.6.6, “Performance Monitoring.”

31.2.4

ABR Flow Control

When AAL5-ABR is enabled, the ATM controller implements the ATM Forum TM 4.0 available-bit-rate

flow. It automatically inserts forward- and backward-RM cells into the user cell stream and adjusts the

transmission rate according to the backwards RM cell feedback; see Section 31.10.2.2.2, “AAL5-ABR

Protocol-Specific RCT.” The ABR flow is controlled on a per-VC basis.

31.3

ATM Pace Control (APC) Unit

The ATM pace control (APC) unit schedules the ATM channels for transmitting. While performing this

task, the APC unit uses the following parameters:

•

Frequency (bandwidth) of each ATM channel

•

ATM traffic pacing—Peak cell rate (PCR), sustain cell rate (SCR), and minimum rate (MCR)

•

Priority level—Real-time channels (CBR or VBR-RT) are scheduled at high-priority levels;

non-real-time channels (VBR-NRT, ABR, UBR) are scheduled at low-priority levels. Up to eight

priority levels are available.

31.3.1

APC Modes and ATM Service Types

The ATM Forum (http://www.atmforum.com) defines the service types described in Table 31-1.

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