Freescale Semiconductor MPC8260 - Manual (Page 928)

ATM Controller and AAL0, AAL1, and AAL5
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
30-8 Freescale Semiconductor
The PowerQUICC II 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.
30.2.2.2.1 AAL1 CES Receiver Overview
Refer to Section 31.3, “AAL1 CES Receiver Overview.”
30.2.2.3 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.
30.2.2.4 AAL2 Receiver Overview
Refer to Section 32.4.1, “Receiver Overview.”
30.2.3 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 30.6.6, “Performance Monitoring.”
30.2.4 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 30.10.2.2.2, “AAL5-ABR
Protocol-Specific RCT.” The ABR flow is controlled on a per-VC basis.
30.3 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.
30.3.1 APC Modes and ATM Service Types
The ATM Forum (http://www.atmforum.com) defines the service types described in Table 30-1 .