PM7385 Datasheet, PDF (53/244 Pages) PMC-Sierra, Inc – Frame Engine and Data Link Manager

DATA SHEET
PMC-1990114
ISSUE 6
8.4.2 Priority Encoder
PM7385 FREEDM-84A672
84 LINK, 672 CHANNEL FRAME ENGINE AND DATA LINK MANAGER
WITH ANY-PHY PACKET INTERFACE
The priority encoder monitors the line interfaces for requests and synchronises
them to the SYSCLK timing domain. Requests are serviced on a fixed priority
scheme where highest to lowest priority is assigned from the line interface
attached to link 0 to that attached to link 83. Thus, simultaneous requests from
link ‘m’ will be serviced ahead of link ‘n’, if m < n. When there are no pending
requests, the priority encoder generates an idle cycle. In addition, once every
fourth SYSCLK cycle, the priority encoder inserts a null cycle where no requests
are serviced. This cycle is used by the channel assigner downstream for host
microprocessor accesses to the provisioning RAMs.
8.4.3 Channel Assigner
The channel assigner block determines the channel number of the data byte
currently being processed. The block contains a 2688 word channel provision
RAM. The address of the RAM is constructed from concatenating the link
number and the time-slot number of the current data byte. The fields of each
RAM word include the channel number and a time-slot enable flag. The time-slot
enable flag labels the current time-slot as belonging to the channel indicated by
the channel number field.
8.4.4 Loopback Controller
The loopback controller block implements the channel based diagnostic loopback
function. Every valid data byte belonging to a channel with diagnostic loopback
enabled from the Transmit HDLC Processor / Partial Packet Buffer block
(THDL672) is written into a 256 word FIFO. The loopback controller monitors for
an idle time-slot or a time-slot carrying a channel with diagnostic loopback
enabled. If either conditions hold, the current data byte is replaced by data
retrieved from the loopback data FIFO.
8.5 Receive HDLC Processor / Partial Packet Buffer
The Receive HDLC Processor / Partial Packet Buffer block (RHDL672)
processes up to 672 synchronous transmission HDLC data streams. Each
channel can be individually configured to perform flag sequence detection, bit de-
stuffing and CRC-CCITT or CRC-32 verification. The packet data is written into
the partial packet buffer. At the end of a frame, packet status including CRC
error, octet alignment error and maximum length violation are also loaded into the
partial packet buffer. Alternatively, a channel can be provisioned as transparent,
in which case, the HDLC data stream is passed to the partial packet buffer
processor verbatim.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE 44