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PMC-Sierra, Inc.
PM5349 S/UNI-QUAD
DATASHEET
PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
45
enabled, cells are dropped if uncorrectable HCS errors are detected, or if the
corrected header contents match the pattern contained in the RXCP Match
Header Pattern and RXCP Match Header Mask registers. Idle or unassigned cell
filtering is accomplished by writing the appropriate cell header pattern into the
RXCP Match Header Pattern and RXCP Match Header Mask registers.
Idle/Unassigned cells are assumed to contain the all zeros pattern in the VCI and
VPI fields. The RXCP Match Header Pattern and RXCP Match Header Mask
registers allow filtering control over the contents of the GFC, PTI, and CLP fields
of the header.
The HCS is a CRC-8 calculation over the first 4 octets of the ATM cell header.
The RXCP block verifies the received HCS using the polynomial, x
8
+ x
2
+ x + 1.
The coset polynomial, x
6
+ x
4
+ x
2
+ 1, is added (modulo 2) to the received HCS
octet before comparison with the calculated result. While the cell delineation
state machine (described above) is in the SYNC state, the HCS verification circuit
implements the state machine shown in Figure 5.
Figure 5: HCS Verification State Diagram
DETECTION
MODE
ATM DELINEATION
SYNC STATE
CORRECTION
MODE
No Errors Detected
In M Cells
(Pass M Cell)
Apparent Multi-Bit Error
(Drop Cell)
Errors
Detected
(Drop Cell)
No Errors
Detected
(Pass Cell)
ALPHA
consecutive
incorrect HCS's
(To HUNT state)
DELTA
consecutive
correct HCS's
(From PRESYNC
state)
Single-Bit Error
(Correct Error
and Pass Cell)
th
No Errors Detected
(Pass Cell)