PMC-Sierra, Inc.
PRELIMINARY
PM5381 S/UNI-2488
DATASHEET
PMC-2000489
ISSUE 1
SATURN USER NETWORK INTERFACE FOR 2488 MBIT/S
10.15.1 ATM Idle/Unassigned Cell Generator
The Idle/Unassigned Cell Generator inserts idle or unassigned cells into the cell stream when
enabled. Registers are provided to program the GFC, PTI, and CLP fields of the idle cell header
and the idle cell payload. The idle cell HCS is automatically calculated and inserted.
10.15.2 ATM Scrambler
The Scrambler scrambles the 48 octet information field. Scrambling is performed using a parallel
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implementation of the self-synchronous scrambler (x + 1 polynomial) described in the
references. The cell headers are transmitted unscrambled, and the scrambler may optionally be
disabled.
10.15.3 ATM HCS Generator
The HCS Generator performs a CRC-8 calculation over the first four header octets. A parallel
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2
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4
2
implementation of the polynomial, x +x +x+1, is used. The coset polynomial, x +x +x +1, is
added (modulo 2) to the residue. The HCS Generator optionally inserts the result into the fifth
octet of the header.
10.15.4 POS PPP/HDLC Frame Generator
The PPP/HDLC Frame Generator runs off of the SONET sequencer to create the POS frames to
be transmitted. Flags are inserted whenever the Transmit FIFO is empty and there is no data to
transmit. When there is enough data to be transmitted, the block operates normally; it removes
packets from the Transmit FIFO and transmits them. In addition, FCS generation, error insertion,
byte stuffing, and scrambling can be optionally enabled.
In the event of a FIFO underflow caused by the FIFO being empty while a packet is being
transmitted, the packet is aborted by transmitting the Abort Sequence. The PPP Abort Sequence
consists of an Escape Control character (0x7D) followed by the Flag Sequence (0x7E). Bytes
associated with this aborted frame are still read from the FIFO but are discarded and replaced
with the Flag Sequence in the outgoing data stream. If an overflow occurs, the packet being
transmitted will also be aborted and the same abort sequence will be added. Transmission of
data resumes when a Start of Packet is encountered in the FIFO data stream.
The POS Frame Generator also performs Inter Packet Gapping. This operation consists of
inserting a programmable number of Flag and Idle Sequence characters between each
PPP/HDLC Frame transmission. This feature allows one to control the system effective data
transmission rate if required.
Proprietary and Confidentail to PMC-Sierra Inc., and for its Customer’s Internal Use
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PMC [ PMC-SIERRA, INC ]
