S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
The length of time required to perform the VC Table search is variable. Since the Primary Search
Key is used in a direct lookup, only one cycle is required to process the Primary Search Key. The
Secondary Search Key processing time is highly dependent on the key’s contents, but the
maximum number of processing cycles required is equal to the number of bits in the Secondary
Search Key which must be examined to make a unique identification. Some VPI and VCI bits
may always be zero; therefore, they need not be used in the search. In some instances, the
Primary Search Key may overlap the Secondary Search Key; therefore, the intersecting bits are
only required for the confirmation of a search. If the number of bits used by the binary search is
no greater than 18, a sustained rate of 5.682x106 cells/s is guaranteed. The general expression for
guaranteed throughput is given below
20
22
1
Throughput =
cells/s
(
2 + max(max.binary tree depth,18))(SYSCLK period)
Note, however, if the binary tree depth is less than 18, the throughput remains 5.68x106 cells/s.
10.2.1 Search Table Data Structure
The Primary and Secondary Search Key table fields reside in the lower 8 Mbits of the external
SRAM (SADDR[17] = 0). Each SRAM word is 64 bits wide. The Primary Table Record entry is
located in bits 17 to 0 of each word and the secondary table record entry is located in bits 63 to
18. There are a total of 128K possible primary and secondary records (all located in the lower 8
Mbits of the external SRAM). The following table shows the format of each 64 bit word in the
lower 8Mbits of the external SRAM.
Table 5 Search Table
63
2
0
1
Selector
(6)
Left
Leaf
(1)
1
Left Branch
(17)
Right
Leaf
(1)
1
Right Branch
(17)
Primary Search
Pointer (17)
Shaded Fields are Reserved, and must be programmed to logic 0 for proper operation.
The figure below illustrates the relationship between the Primary Search Table Key, Secondary
Search Table Key and the VC Table and shows the search tree’s that are used in connection
identification.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
77
PMC [ PMC-SIERRA, INC ]
