![](http://datasheet.mmic.net.cn/260000/PM7390-BI_datasheet_15944927/PM7390-BI_91.png)
Multi-Service Access Device For Channelized Interfaces
Telecom Standard Product Data Sheet
Production
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990823, Issue 4
91
11.15 Receive Cell and Frame Processor (RCFP)
The Receive Cell and Frame Processor (RCFP) performs both ATM and PPP processing. It has
the capability to process a single STS-12c/STM-4c channel or a single STS-48c/STM-16c
channel.
RCFP ATM Cell Processor
In ATM mode, the RCFP performs ATM cell delineation, provides cell filtering based on
idle/unassigned cell detection and HCS error detection, and performs ATM cell payload
descrambling. Details on each of these functions can be found in the RTDP description.
RCFP POS Frame Processor
The RCFP performs PPP packet extraction, provides FCS error detection, performs packet
payload descrambling, and provides performance monitoring functions. Details on each of these
functions can be found in the RTDP description. Note that the RCFP only processes byte
synchronous PPP, not bit synchronous HDLC.
The RCFP handles malformed packets (smaller than 4 bytes) differently than the RTDP. In the
RCFP, the minimum packet violation is counted in MINPL, while for the RTDP, they only cause
MINPLI to be asserted. Note that the FCS calculation in the RCFP will proceed independent of
any errors detected upstream. Thus, under abort, max length violations, etc, one might also get
FCS violations.
11.16 PHY-to-Layer Decoupling FIFO (RXSDQ)
The RXSDQ provides FIFOs for each channel to separate the receive line-side timing from the
higher layer ATM system timing. FIFO space can be allocated to different channels in blocks of
16 bytes. The receive FIFO holds a maximium of 768 blocks. For instance, if the S/UNI-
MACH48 is configured to carry one STS-12c and 36 STS-1 POS channels, the FIFO can allocate
space for 192 blocks for the STS-12c channel and 16 blocks for each of the 36 STS-1s. This
would fully utilize the entire FIFO storage space. The maximum value that can be allocated to
any single channel is 192 blocks.
The RXPHY provides either a Utopia Level 3 or a POS-PHY Level 3 interface to read data from
the FIFO.
ATM Receive FIFO
The Receive FIFO is responsible for holding cells until they are read by Receive System
Interface.
Receive FIFO management functions include filling the receive FIFO, indicating when cells are
available to be read from the receive FIFO, maintaining the receive FIFO read and write pointers,
and detecting FIFO overrun conditions. Upon detection of an overrun, the FIFO discards the
current cell and subsequent cells until there is room in the FIFO. FIFO overruns are indicated
through a maskable interrupt and register bit and are considered a system error.