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PM7329 S/UNI-APEX-1K800
DATASHEET
PMC-2010141
ISSUE 2
ATM TRAFFIC MANAGER AND SWITCH
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
63
The masked write mechanism is provided to allow the microprocessor to change
a field within a word in context memory while traffic is present, without risk of
context corruption. The masked write can be performed on one word per
operation. In this mode (as indicated in the control register), the second word in
the 4-word burst write buffer and the second pair of bits in the overflow register
represent a bit mask which will be used by S/UNI-APEX-1K800 to perform a
masked write function.
10.8 SAR Assist
The SAR assist module allows cells or AAL5 frames to be transferred to and
from the queue engine. Burst transfers from the microprocessor into and out of
the SAR staging buffers enable efficient access to the queuing structures. The
staging buffers are organized as 64 byte units, including the ICI/ECI, the cell
header, the payload, and control or status information. A complete buffer can be
written or read in one continuous burst, or the data can be accessed individually
or with a series of shorter bursts. Within this structure, both the cell header and
the payload are aligned on 32-bit boundaries, to simplify microprocessor access.
The SAR assist module can also optionally perform calculation, checking, and
insertion of AAL5 CRC32 or CRC10.
One staging buffer is provided for cell or frame injection, while four staging
buffers are provided for cell or frame reception (one for each microprocessor
class queue).
10.8.1 Transmit
The transmit function of the SAR has the following features:
Read staging buffer for each of the 4 class queues associated with the
microprocessor.
CRC-32 checking for AAL5 re-assembly.
Simultaneous re-assembly assist on all 4 class queues.
CRC-10 checking for OAM.
Cell header is provided with each PDU, including PTI for end-of-message
detection by the microprocessor.
Each read buffer represents a 2-cell pipeline, providing minimum latency for cell
retrieval. While a cell is read out, a second cell is retrieved from the queue
engine automatically. By having read buffers for each class, the microprocessor
can decide which class has the highest priority. The microprocessor can