PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 103

• Manufacturer Part Number: PM5381-BI
• Description: ATM UNI, Single Channel ATM PHY Interface for 2488.32Mbps
• Manufacturer: PMC-Sierra, Inc.

10.15 Transmit Cell and Frame Processor (TCFP)
10.15.1 ATM Idle/Unassigned Cell Generator
10.15.2 ATM Scrambler
10.15.3 ATM HCS Generator
10.15.4 POS PPP/HDLC Frame Generator
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
The Transmit Cell and Frame Processor (TCFP) performs both ATM and PPP processing. It has
the capability to process a single STS-48c (STM-16c) channel. In ATM mode, the TCFP performs
provides rate adaptation via idle/unassigned cell insertion, provides HCS generation and
insertion, and performs ATM cell scrambling. In POS mode, the TCFP provides rate adaptation
by transmitting flag sequences (0x7E) between packets, provides FCS generation and insertion,
performs packet data scrambling, and provides performance monitoring functions.
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.
The Scrambler scrambles the 48-octet information field. Scrambling is performed using a parallel
implementation of the self-synchronous scrambler (x
references. The cell headers are transmitted unscrambled, and the scrambler may optionally be
disabled.
The HCS Generator performs a CRC-8 calculation over the first four header octets. A parallel
implementation of the polynomial, x
added (modulo 2) to the residue. The HCS Generator optionally inserts the result into the fifth
octet of the header.
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.
8
+x
2
+x+1, is used. The coset polynomial, x
S/UNI-2488 Telecom Standard Product Datasheet
43
+ 1 polynomial) described in the
6
+x
4
+x
2
+1, is
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