
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
4-15
Table 4-6. Segmentation VCC Table Entry—AAL3/4, 5, and 0 Field Descriptions (1 of 2)
Field Name
Description
PM_INDEX
Performance Monitoring index. 128 VCCs can be selected for automatic OAM PM generation. Each
monitored VCC has a unique performance monitoring index.
If this field is changed while the VCC is active, only the byte containing the field should be written.
ACK_PM
Toggled after each backward reporting PM cell is sent. Used to prevent PM information in PM table from
being overwritten before cell is sent.
FWD_PM
Indicates that next cell should be forward monitoring PM cell.
LAST_PNTR
Points to last buffer descriptor currently linked to the VCC. The two least significant bits of the pointer
are assumed to be 0 (word-aligned). The address of the buffer descriptor is (LAST_PNTR << 2) or
(LAST_PNTR x 4).
UU
AAL5 User-to-User indication. This field is copied from the buffer descriptor UU field. The CN8236
inserts the UU field in the CPCS-PDU trailer contained in the EOM cell.
BOM_PNTR
In Message mode (STM_MODE=0), points to the first buffer descriptor of a message composed of more
than one buffer descriptor. The CN8236 returns the corresponding USER_PNTR from this buffer
descriptor in the status queue.
In Streaming mode (STM_MODE=1), it is not used.
The two least significant bits of the pointer are assumed to be zero (word-aligned). The address of the
buffer descriptor is (BOM_PNTR<<2) or (BOM_PNTR * 4).
ATM_HEADER
Used for each ATM cell for the VCC. The transmitted header may be modified by option bits in the
current buffer descriptor.
PDU_LEN
CPCS-PDU Trailer Length field. This field is generated by the SAR and inserted in the Length field of the
EOM cell.
BUFFER_LEN
Buffer Length. The number of bytes of data read from the current segmentation buffer.
PORT_ID
Identifies the Physical Device (Port) ID for the VCC.
CRC_REM
Accumulated value of AAL5 32-bit CRC, calculated on-the-fly by the SAR and appended to the PDU at EOM.
BETAG
AAL3/4 Btag and Etag fields.
SN
AAL3/4 Sequence Number field.
MID
AAL3/4 Message Id field.
STM_MODE
Streaming Status Mode.
0 = Message Mode—a status entry is written (with a corresponding maskable interrupt) only when the
last buffer in a message completes segmentation. The status entry written corresponds to the first
buffer descriptor in the message.
1 = Streaming Mode—a status entry is written (with a corresponding maskable interrupt) for each buffer
as it completes segmentation.
STAT/HPORT_ID
Identifies the Segmentation Status Queue used for all status entries, or if the AALx_EN bit is set,
identifies the AALx port.
PM_EN
Enables performance monitoring for the VCC. If this bit is changed while the VCC is active, only the byte
LAST_CLP
Last transmitted CLP bit for VCC. This bit is updated by the SRC after each transmitted cell. This bit is in
the same word as the PM_EN bit, and is copied by the SAR from the current buffer descriptor. The bit is
used to select the correct VBR bucket for certain VBR VCCs.