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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
43
Path RDI alarm is detected by extracting bit 5 of the path status byte. The PRDI
signal is set high when bit 5 is set high for five/ten consecutive frames. PRDI is
set low when bit 5 is low for five/ten consecutive frames. Auxiliary RDI alarm is
detected by extracting bit 6 of the path status byte. The Auxiliary RDI alarm is
indicated when bit 6 is set high for five/ten consecutive frames. The Auxiliary RDI
alarm is removed when bit 6 is low for five/ten consecutive frames. The
Enhanced RDI alarm is detected when the enhanced RDI code in bits 5,6,7 of
the path status byte indicates the same error codepoint for five/ten consecutive
frames. The Enhanced RDI alarm is removed when the enhanced RDI code in
bits 5,6,7 of the path status byte indicates the same non error codepoint for
five/ten consecutive frames. The ERDII maskable interrupt is set high when bits
5, 6 & 7 of the path status byte (G1) byte are set to a new codepoint for five or ten
consecutive frames. The ERDIV[2:0] signal reflects the state of the filtered ERDI
value (G1 byte bits 5, 6, & 7).
10.6
Receive ATM Cell Processor (RXCP)
The Receive ATM Cell Processor (RXCP) performs ATM cell delineation,
provides cell filtering based on idle/unassigned cell detection and HCS error
detection, and performs ATM cell payload de-scrambling. The RXCP also
provides a four cell deep receive FIFO. This FIFO is used to separate the STS-3c
(STM-1) line timing from the higher layer ATM system timing.
10.6.1
Cell Delineation
Cell Delineation is the process of framing to ATM cell boundaries using the
header check sequence (HCS) field found in the cell header. The HCS is a
CRC-8 calculation over the first 4 octets of the ATM cell header. When
performing delineation, correct HCS calculations are assumed to indicate cell
boundaries. Cells are assumed to be byte-aligned to the synchronous payload
envelope. The cell delineation algorithm searches the 53 possible cell boundary
candidates individually to determine the valid cell boundary location. While
searching for the cell boundary location, the cell delineation circuit is in the HUNT
state. When a correct HCS is found, the cell delineation state machine locks on
the particular cell boundary, corresponding to the correct HCS, and enters the
PRESYNC state. The PRESYNC state validates the cell boundary location. If
the cell boundary is invalid, an incorrect HCS will be received within the next
DELTA cells, at which time a transition back to the HUNT state is executed. If no
HCS errors are detected in this PRESYNC period, the SYNC state is entered.
While in the SYNC state, synchronization is maintained until ALPHA consecutive
incorrect HCS patterns are detected. In such an event a transition is made back
to the HUNT state. The state diagram of the delineation process is shown in
Figure 4.