PMC-Sierra PM5349 manual Receive ATM Cell Processor Rxcp, Cell Delineation

PMC-Sierra, Inc.

S/UNI-QUAD

DATASHEET

PM5349 S/UNI-QUAD

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

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.

10.6.1Cell 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.

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