MPC8280 datasheet(1120/1386 Pages) FREESCALE

1120 / 1386 page

ATM AAL2

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

33-14

Freescale Semiconductor

33.3.5.3

CPS Buffer Structure

The CPS buffer structure consists of a BD table that points to data buffers. The BDs contain, apart from

the buffer pointer, also the packet header. The buffers contain the packet payload. See Figure 33-8.

Figure 33-8. Buffer Structure Example for CPS Packets

0x0A

—

Number of

Packets In

Queue

Counts the number of packets currently in the queue. If this queue is switched, the

receiver increments this counter with each new received packet and the transmitter

decrements it with each packet sent. For switching, the user should initialize this

counter to zero. When this queue is not switched, this counter counts down with every

packet sent. (This can have various purposes such as evaluating the packet rate that

is transmitted from this queue.).

0x0C

—

NextQueue

Points to the next TxQD to be serviced after this one. See Section 33.3.2, “Transmit

Priority Mechanism.”

0x0E

—

Reserved, should be cleared during initialization.

Boldfaced entries must be initialized by the user.

Table 33-2. CPS TxQD Field Descriptions (continued)

Offset

Bits

Name1

Description

BD memory space

TxBD_Table_Base

TxBD table

of ch 1

TxBD table

of ch 4

TxBD_Table_Offset_Out

Pointers

TxBD 1

TxBD 2

TxBD 3

TxBD 4

TxBD 5

TxBD 6

TxBD 7

TxBD 8

TxBD 9

TxBD 1

TxBD 2

TxBD 3

TxBD 4

TxBD 5

TxBD 6

Tx buffer 3 of

channel 1

Tx buffer 4 of

channel 1

Tx buffer 1 of

channel 4

Tx buffer 2 of

channel 4

Tx buffer 3 of

channel 4

Tx buffer 2 of

channel 1

Tx buffer 8 of

channel 4

•

Tx buffer 1 of

channel 1

Data memory space

from

CPS TxQD

Pointers

from

another

CPS TxQD

TxBD_Table_Base

TxBD_Table_Offset_Out

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