Freescale Semiconductor MPC8260 - Manual (Page 1081)

ATM AAL2
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 32-19
32.3.5.5 SSSAR Transmit Buffer Descriptor
The SSSAR buffer structure consists of a BD table that points to data buffers. The buffers may contain
SSSAR SDUs belonging to different CIDs. Each buffer may contain a whole SSSAR SDU or part of it.
The CPS CID is located in the first BD of the SSSAR SDU. See
Figure 32-12 .
.
0 1 2 3 4 5 7 8 15
Offset + 0x00 R CM W I L — CID
Offset + 0x02 Data Length (DL)
Offset + 0x04 Tx Data Buffer Pointer (TXDBPTR)
Offset + 0x06
Figure 32-12. SSSAR TxBD
Table 32-5. SSSAR TxBD Field Descriptions
Offset Bits Name
1
Description
0x00 0 R 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.
1 CM 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.
2 W 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.
3 I 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 L Last.
0 This is not the last buffer of the SSSAR SDU.
1 This is the last buffer of the SSSAR SDU.
5-7 — Reserved, should be cleared during initialization.
8-15 CID Contains the CID number of the SSSAR SDU pointed by this BD. This field should be
written to the first BD of an SSSAR SDU.