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4.0 Segmentation Coprocessor
4.2 Segmentation Functional Description
RS8234
Datasheet for RS8234 xBR ServiceSAR
N8234DS1B
4.2.1.1 VCC
Identification
The Host allocates a region of SAR shared memory for the Segmentation VCC
Table at system initialization, based on the maximum number of connections and
the maximum number of ABR connections. The Host informs the SAR of the
location of the table through the internal base register, SEG_VBASE
(SEG_VCCB).
Once a table has been established, the Host assigns segmentation VCCs to
entries in the table. The Host describes the Seg VCC by initializing the Seg VCC
Table entry including the SCH_STATE portions of the assigned VCC. The
VCC_INDEX, defined as the offset into the table in 10 word increments,
uniquely identifies a segmentation channel. In all communication between the
SAR and the Host, a VCC_INDEX field specifies a VCC.
4.2.2 Submitting Segmentation Data
Once the Host establishes a connection, it supplies data for segmentation. The
Host submits full or partial PDUs, either one at a time or in batches, for individual
VCCs. The SAR accepts PDUs at any time, regardless of the state of the connec-
tion, and segments data on each VCC independently.
4.2.2.1 User Data
Format
The RS8234 accepts user PDUs as sequences of data buffers. SAR shared mem-
ory resident segmentation buffer descriptors (SBDs) provide the address, length,
and control information for buffers. The Host forms PDU buffer sequences by
linking buffer descriptors. The data buffers themselves contain only user data and
reside in Host (or optionally SAR shared) memory.
NOTE:
(Note: SAR shared memory data buffer segmentation should be limited to
low bandwidth applications, such as Signalling, OAM, and ILMI).
Host data buffers contain the bulk of segmentation data, and can begin on any
byte-aligned address in the SARs PCI address space.
4.2.2.2 Buffer
Descriptors
The Host submits data using the following process sequence. First, the Host allo-
cates an SBD for each buffer in a message. SBDs reside in SAR shared memory,
and must begin on word-aligned addresses. Then, the Host describes the buffers
in the SBD. This description includes the address and length of the buffer, as well
as control fields for the SAR during buffer segmentation. These control fields
specify the VCC_INDEX, the AAL type, and header override information for the
buffer.
The Host then creates PDU message sequences by concatenating buffers. The
Host forms the buffer sequence by linking a list of buffer descriptors using the
SBDs NEXT field. Two bits in the SBD control fields delineate the beginning and
end of messages. One bit, BOM, specifies that the buffer contains the beginning
of a message. The second bit, EOM, notifies the SAR that the buffer contains the
end of the current message. Table 4-1 shows the appropriate utilization of these
bits in detail. The host identifies the end of the SBD chain by terminating the list
with a NULL (0) NEXT pointer.