MPC8280 datasheet(1121/1386 Pages) FREESCALE

1121 / 1386 page

ATM AAL2

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

33-15

Figure 33-9 shows a CPS TxBD.

Table 33-3 describes the CPS TxBD fields.

Offset + 0x00

—

CPS Packet Header

Offset + 0x02

CPS Packet Header

Offset + 0x04

Tx Data Buffer Pointer (TXDBPTR)

Offset + 0x06

Figure 33-9. CPS TxBD

Table 33-3. CPS TxBD Field Descriptions

Offset

Bits

Name1

Boldfaced entries must be initialized by the user.

Description

0x00

Ready

0 The buffer associated with this BD is not ready for transmission. The user is free

to manipulate this BD or its associated buffer. The CP clears R after the buffer is

sent or after an error condition is encountered.

1 The user-prepared buffer has not been sent or is currently being sent. No fields of

this BD may be written by the user once R is set.

CM2

2 Setting Continuous mode (TxBD[CM] = 1) is not allowed in CID switching mode.

Continuous mode

0 Normal operation.

1 The CP does not clear R after this BD is closed, allowing the associated buffer to

be retransmitted automatically when the CP next accesses this BD. However, the

R bit is cleared if an error occurs during transmission, regardless of the CM bit

setting.

Wrap (final BD in table)

0 This is not the last BD in the TxBD table.

1 This is the last BD in the TxBD table. After this buffer is used, the CP transmits

outgoing data for this channel from the first BD in the table (the BD pointed to by

the channel’s TxBD_table_Base in the TxQD). The number of TxBDs in this table

is determined only by the W bit.

Interrupt

0 No interrupt is generated after this buffer has been serviced.

1 A Tx Buffer event is sent to the interrupt queue after this buffer is serviced. The

GHIN/GLIN bit in the event register is set when the INT_CNT counter reaches

terminal count.

4–7

—

Reserved, should be cleared during initialization.

8–15

CPS Packet

Header

This field contains the beginning (MSB) of the 3-byte packet header. See

Figure 33-10 for the CPS packet header format.

0x02

—

CPS Packet

Header

This field contains the rest of the packet header. If TxQD[HEC] = 0, the HEC part of

the packet header is calculated by the CP, and the user may disregard the five

least-significant bits of this field. See Figure 33-10 for the CPS packet header format.

0x04

—

TXDBPTR

Tx data buffer pointer. Points to the address of the associated buffer. There are no

byte-alignment requirements for the buffer, and it may reside in either internal or

external memory. This pointer is not modified by the CP.

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