MPC8280 datasheet(1127/1386 Pages) FREESCALE

1127 / 1386 page

ATM AAL2

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

33-21

•

RxQD offsets from 8 through 511 point into the internal RxQD table located in dual-port RAM at

RxQD_Base_Int. Note that the first 32 bytes of the internal RxQD table are reserved (so offsets

0–7 are reserved).

•

RxQD offsets greater than 511 point into the external RxQD table located at RxQD_Base_Ext +

(512*4).

•

Because the three types of RxQDs are different sizes, some offset numbers may not be used.

Figure 33-13. CID Mapping Process

33.4.3

AAL2 Switching

Switching is performed by pointing an RX CID at a switch RxQD (see Figure 33-14). The switch RxQD

is unique for each Rx CID. The descriptor holds a translation CID number and a pointer to a CPS TxQD

into which this packet is saved and later sent by the transmitter. (The TxQD pointer is responsible for the

actual PHY | VP | VC switching.) The TxQD pointed to by the switch RxQD(s) should have TxQD[SW]

set and should not be modified by the host when the channel is active. The transmit scheduling of the

packet is done by the APC according to the programmed bit rate of the ATM channel that holds the

switched queue.

RxQD table (internal)

2044

Reserved

SSSAR RxQD

CPS RxQD

Switch RxQD

RxQD table (external)

2048

CPS RxQD

Switch RxQD

RxBD table

Tx queue descriptor

TxBD table

Rx buffers

Tx buffers

RxQD_Base_Int +

RxQD_Offset*4

CID mapping table

RxQD offset

CID0

CID1

CID255

RxQD_Base_Ext + 512*4

(in FCC parameter RAM)

RxQD offset

•

Half-word

CID mapping table base

RxQD_Base_Int

(in FCC parameter RAM)

AAL2 RCT

ATM cell

Header

STF

CID-PH

CPS packet payload

CID-PH

CPS packet payload

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