T8207 Datasheet, PDF (27/158 Pages) Agere Systems – ATM Interconnect

Advance Data Sheet
September 2001
CelXpres T8207
ATM Interconnect
8 Look-Up Table
Cells arriving from the UTOPIA bus obtain information from the external static RAM look-up table (LUT), which is
divided among VPI, VCI, and OAM/RM records. Each of these records contains specific VPI or VPI/VCI translation
and cell bus routing information. The size of the records is programmable to 8 bytes or an extended 16 bytes. The
16-byte mode adds two 32-bit counters to each record. The 16-byte mode is discussed in Section 8.4, Extended
Records.
The VPI value in the header, in addition to the PHY port number, of the incoming cell points to a VPI record in the
look-up table. This VPI record is examined first. If the VPI record indicates OAM F4 routing, the OAM record, to
which the VPI record points, provides the OAM routing and VPI/VCI translation information. If OAM F4 routing is
not indicated, information about the type of translation, VPI only or VPI/VCI, is obtained from the original VPI
record. For VPI only translation, routing information is obtained from the VPI record, and full or partial VPI transla-
tion is performed.
For VPI/VCI translation, the VPI record points to the appropriate VCI record, where VPI/VCI translation and routing
information is stored. If the VCI record indicates OAM F5 routing, the OAM record, to which the VCI record points,
provides the OAM routing and VPI/VCI translation information. If no OAM F5 routing is indicated, VPI/VCI transla-
tion and cell routing is performed using the information in the VCI record.
8.1 Look-Up Table RAM
The number of memory devices (up to two) used for the look-up table and the size of the external SRAM are pro-
grammable. The tram_qnty_sel bit in the main configuration 1 register (address 0100h) specifies whether one or
two RAM chips are used. If two memory devices are used, separate chip select signals are generated. These chip
selects are created from the decoded RAM addresses. The tram_size configuration bits, also in the main configu-
ration 1 register, are used to select memory sizes of 32 Kbytes, 64 Kbytes, 128 Kbytes, or 256 Kbytes. Therefore,
the maximum look-up table size of 512 Kbytes is realized when two RAM chips of 256 Kbytes each are used.
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