MPC8280 datasheet(1093/1386 Pages) FREESCALE

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ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-33

10–11

ATT

ATM traffic type

00 Peak cell-rate pacing. The host must initialize PCR and the PCR fraction. Other

traffic parameters are not used.

01 Peak and sustain cell rate pacing (VBR traffic). The APC performs a

continuous-state leaky bucket algorithm (GCRA) to pace the channel-sustain cell

rate. The host must initialize PCR, PCR fraction, SCR, SCR fraction, and BT (burst

tolerance).

10 Peak and minimum cell rate pacing (UBR+ traffic). The host must initialize PCR, PCR

fraction, MCR, MCR fraction, and MDA.

11 Reserved.

AVCF

Auto VC off. Determines APC behavior when the last buffer associated with this VC has

been sent and no more buffers are in the VC’s TxBD table,

0 The APC does not remove this VC from the schedule table and continues to schedule

it to transmit.

1 The APC removes this VC from the schedule table. To continue transmission after the

host adds buffers for transmission, a new ATM TRANSMIT command is needed, which

can be issued only after the CP clears the VCON bit. (Bit 13)

VCON

Virtual channel is on

Should be set by the host before it issues an ATM TRANSMIT command. When the host

sets TCT[STPS] (stop transmit), the CP deactivates this channel and clears VCON

when the channel is next encountered in the APC scheduling table. The host can issue

another ATM TRANSMIT command only after the CP clears VCON.

14–15

INTQ

Points to one of four interrupt queues available.

0x02

0–12

—

Reserved, should be cleared during initialization.

13–15

AAL

AAL type

000 AAL0 —Reassembly with no adaptation layer

001 AAL1 —ATM adaptation layer 1

010 AAL5 —ATM adaptation layer 5.

100 AAL2 —ATM adaptation layer 2. Refer to Chapter 33, “ATM AAL2.”

101 AAL1_CES —ATM adaptation layer 1 with circuit emulation service

All others reserved.

0x04

—

TxDBPTR

Tx data buffer pointer. Holds the real address of the current position in the Tx buffer.

0x08

—

TBDCNT

Transmit BD count. Counts the remaining data to transmit in the current transmit buffer.

Its initial value is loaded from the data length field of the TxBD when a new buffer is

open; its value is subtracted for any transmitted cell associated with this channel.

0x0A

—

TBD_Offset

Transmit BD offset. Holds offset from TBD_BASE of the current BD. Initialize to 0.

0x0C

0–7

Rate

Reminder

Rate remainder. Used by the APC to hold the rate remainder after adding the pace

fraction to the additive channel rate. Initialize to 0.

8–15

PCR Fraction Peak cell rate fraction. Holds the peak cell rate fraction of this channel in units of 1/256

slot. If this is an ABR channel, this field is automatically updated by the CP.

0x0E

—

PCR

Peak cell rate. Holds the peak cell rate (in units of APC slots) permitted for this channel

according to the traffic contract. Note that for an ABR channel, the CP automatically

updates PCR to the ACR value.

0x10

—

Protocol-specific

0x16

—

APCLC

APC linked channel. Used by the CP. Initialize to 0 (null pointer).

0x18

—

ATMCH

ATM cell header. Holds the full (4-byte) ATM cell header of the current channel. The

transmitter appends ATMCH to the cell payload during transmission.

Table 32-7. TCT Field Descriptions (continued)

Offset

Bits

Name

Description

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