PMC-Sierra PM5349 manual HCS Verification State Diagram

PMC-Sierra, Inc.

S/UNI-QUAD

DATASHEET

PM5349 S/UNI-QUAD

PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)

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, x8 + x2 + x + 1. The coset polynomial, x6 + x4 + x2 + 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

ATM DELINEATION

SYNC STATE

ALPHA consecutive incorrect HCS's (To HUNT state)

		Apparent Multi-Bit Error
		(Drop Cell)
No Errors	CORRECTION
Detected		Single-Bit Error
	MODE
(Pass Cell)
		(Correct Error
			Errors
		and Pass Cell)
			Detected
			(Drop Cell)
		DETECTION
		MODE
DELTA	No Errors Detected
	In M Cells
consecutive
	(Pass Mth Cell)
correct HCS's		No Errors Detected

(From PRESYNC	(Pass Cell)
state)

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