T-8207-BAL-DB View Datasheet(PDF) - Agere -> LSI Corporation
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T-8207-BAL-DB Datasheet PDF : 158 Pages
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Advance Data Sheet
September 2001
CelXpres T8207
ATM Interconnect
8 Look-Up Table (continued)
8.3 Look-Up Procedure
Look-up procedure is discussed in terms of 8-byte records. Differences in look-up procedures for 8-byte records
and 16-byte records will be discussed in Section 8.4, Extended Records. When a cell is received, the set
lutX_vpi_mask bits in the LUT X configuration structure (Table 103) indicate which incoming VPI bits are used to
address the VPI record in the look-up table. The selected incoming VPI bits are concatenated and multiplied by
eight (for 8-byte records) to create an offset into the table. The sum of this offset and the VPI base address, found
in the LUT X configuration structure, creates the actual look-up table address for the VPI record associated with
the cell. Note that only bits 3 through 18 of the VPI base address are stored in the LUT X configuration structure. If
the lutX_vpi_chk bit is set, all unused VPI bits in the cell header must be ‘0,’ or the cell will be considered out of
range. If the port is configured as UNI, the upper four VPI bits (GFC field) will be ignored in the verification. When
the cell is out of range, it is discarded and not counted as a received cell.
The validity of the accessed VPI record is determined by checking its active (A) and ignore (I) bits. If the cell is
valid, the enable OAM/RM routing (E) bit is consulted to determine if F4 type OAM cell treatment should occur.
(See the definition for these bits in Section 8.2, Organization.)
When the E bit is set and the incoming VCI is less than 32, the OAM record associated with the cell is read. To cal-
culate the translation record address for the OAM/RM cell, the incoming VCI is multiplied by eight (for 8-byte
records), and the resulting product is added to the port’s OAM base address. (See Section 8.2, Organization.) A
special case exists when the incoming VCI is six and the PTI in the cell header is “110.” For this case, the OAM
translation record address is the sum of the port’s OAM base address and 100h.
Next, the validity of the F4 OAM record is determined by checking its A and I bits. If it is valid, the cell is routed as
described by the OAM routing control (C1, C0) bits. (See the definition for these bits in Section 8.2, Organization.)
If the E bit in the VPI record is not one or if the C1 and C0 bits in the OAM record are zero and one, respectively,
the cell does not receive OAM routing. If the cell is not routed OAM, the virtual path routing bit (P bit) in the original
VPI is checked to determine if the cell receives VPI only or VPI/VCI routing. If the P bit indicates VPI only routing,
the cell’s VPI is replaced as indicated by the switch VPI high and low (SH, SL) bits in the VPI only translation
record. (See the definition for these bits in Section 8.2, Organization.) The cell bus routing header and tandem
routing header are then added to the cell, and the cell is transmitted on the cell bus.
If the P bit indicates VPI/VCI routing, the VCI translation record is accessed using the VCI offset and max VCI
value bits in the VPI for VPI/VCI translation record. (The VCI offset and max VCI value bits are described in Sec-
tion 8.2, Organization.) Again, the validity of the VCI translation record is determined by checking its A and I bits.
Next, if the cell is valid, the E bit in the VCI record and the most significant bit of the PTI value in the cell header are
examined to determine if F5 type OAM cell treatment should occur. The value of the incoming cell’s PTI and port
number determines the address in the OAM/RM record space. The following table outlines the look-up table offsets
used for 8-byte records. The OAM translation record address is the sum of this offset and the port’s OAM base
address.
Table 14. F5 Translation Record Addresses Table—8-Byte Records
PTI
“100”
“101”
“110”
“111”
OAM Translation Offset
Port’s OAM base address plus 108h
Port’s OAM base address plus 110h
Port’s OAM base address plus 118h
Port’s OAM base address plus 120h
Agere Systems Inc.
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