CN8236
4.0 Segmentation Coprocessor
ATM ServiceSAR Plus with xBR Traffic Management
4.3 Segmentation Control and Data Structures
28236-DSH-001-A
Mindspeed Technologies
4-21
AAL_OPT
Options for AAL_MODE:
For AAL_MODE = AAL0
00 = Normal operation
01 = SINGLE
10 = Reserved
11 = Reserved
For AAL_MODE = AAL3/4 or AAL5
00 = Normal operation
01 = ABORT
SINGLE: LENGTH is ignored and 48-octets are read from buffer to form the payload of a single ATM
cell. VCC table entry CRC_REM, BUFF_LENGTH, and PDU_LENGTH are not affected. By using the
LINK_HEAD bit in the transmit entry, the buffer descriptor is linked at the start of buffer descriptor
chain for VCC. This means that there are no concerns with mid-cell insertion and that the cell has low
latency. This is intended for OAM cells.
NOTE: This option MUST be set in the buffer descriptor for any Tx Queue entry with LINK_HEAD set.
To do otherwise may result in corrupted SEG data.
ABORT: Send AAL3/4 or AAL5 ABORT cell (no data is read from segmentation buffer). A buffer that
has both ABORT and BOM set is returned without sending an abort cell.
CELL
0 = CN8236 reads the 48-octet payload of ATM cells from memory and generates the ATM header internally.
1 = The CN8236 reads the entire 52-octet ATM cell from segmentation buffer. The ATM_HEADER
stored in the VCC table entry is not used in this mode, and AAL_MODE is ignored.
BOM
1 = Buffer contains the beginning of a message. (See
Table 4-1.)EOM
1 = Buffer contains the end of a message. (See
Table 4-1.)LENGTH
Number of bytes of data contained in the segmentation buffer. Local memory, non-EOM buffer lengths
must be multiples of 4 bytes (mod 4). Maximum allowable size is 64 KB.
GFC_DATA
Data for WR_GFC option.
WR_GFC
0 = The CN8236 generates the GFC field from the VCC table entry ATM_HEADER field.
1 = The CN8236 overwrites the ATM header GFC field for all cells in the buffer with GFC_DATA.
Global GFC changes (active for all buffers of VCC) can be set in the VCC table entry ATM header.
This bit is active only when HEADER_MOD is set.
WR_PTI
0 = The CN8236 generates the PTI field from the VCC table entry ATM_HEADER field.
1 = The CN8236 overwrites the ATM header PTI field for all cells in the buffer with PTI_DATA.
The host can use this feature to generate F5 and PM OAM cells. (See
Chapter 7.0.)This bit is active only when HEADER_MOD is set.
This bit disables PM TUC and BIP16 calculations.
WR_VCI
0 = The CN8236 generates the VCI field from the VCC table entry ATM_HEADER field.
1 = The CN8236 overwrites the ATM header VCI field for all cells in the buffer with
(0x0000|VCI_DATA). (MSBs of VCI are set to 0.)
This bit is active only when HEADER_MOD is set.
This bit disables PM TUC and BIP16 calculations.
PTI_DATA
Data for WR_PTI option. Normally used to generate OAM cells.
VCI_DATA
Data for WR_VCI option. Normally used to generate OAM cells.
NEW_VCI
Data for the RPL_VCI. The CN8236 overwrites the VCC table entry ATM_HEADER VCI field with this
data. Therefore, the effect is permanent until the next buffer descriptor with RPL_VCI is processed.
Table 4-13. Segmentation Buffer Descriptor Field Descriptions (2 of 3)
Field Name
Description