Freescale Semiconductor MPC8260 - Manual (Page 1078)

ATM AAL2
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
32-16 Freescale Semiconductor
Table 32-3 describes the CPS TxBD fields.
.
0 1 2 3 4 7 8 15
Offset + 0x00 R CM W I — CPS Packet Header
Offset + 0x02 CPS Packet Header
Offset + 0x04 Tx Data Buffer Pointer (TXDBPTR)
Offset + 0x06
Figure 32-9. CPS TxBD
Table 32-3. CPS TxBD Field Descriptions
Offset Bits Name
1
1
Boldfaced entries must be initialized by the user.
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
2
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.
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.
4-7 — 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 32-10 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 32-10 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.