PM7311 pmc-sierra, PM7311 Datasheet - Page 73

• Manufacturer Part Number: PM7311
• Description: Freedm 84a1024l Assp Telecom Standard Datasheet
• Manufacturer: pmc-sierra

Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2021832, Issue 2
10.9.4
block. The roamer informs the partial packet reader of the HDLC channel to process. The reader
transfers the data to the RFRAG until the HDLC channel transfer size is reached or an end of
packet is detected. The reader then informs the roamer that a transaction is consumed. The
roamer updates its transaction count and clears the non-zero transaction count flag if required.
The roamer then services the next HDLC channel with its transaction flag set high.
The writer and reader determine empty and full FIFO conditions using flags. Each block in the
partial packet buffer has an associated flag. The writer sets the flag after the block is written and
the reader clears the flag after the block is read. The flags are initialized (cleared) when the block
pointers are written using indirect block writes. The writer declares an HDLC channel FIFO
overrun whenever the writer tries to store data to a block with a set flag. In order to support
optional removal of the FCS from the packet data, the writer does not declare a block as filled (set
the block flag nor increment the transaction count) until the first double word of the next block in
the HDLC channel FIFO is filled. If the end of a packet resides in the first double word, the
writer declares both blocks as full at the same time. When the reader finishes processing a
transaction, it examines the first double word of the next block for the end-of-packet flag. If the
first double word of the next block contains only FCS bytes, the reader would, optionally, process
next transaction (end-of-packet) and consume the block, as it contains information not transferred
to the RFRAG block.
Receive Fragment Builder (RFRAG)
The receive fragment builder re-constructs datagrams from the incoming data stream, moves data
chunks from the partial packet processor into external memory, and manages the assignment of
free external memory addresses to data chunks. The receive fragment builder also discards
datagrams under the following conditions:
·
number of datagrams are waiting to be processed by the re-sequencer.
·
channel’s chunk storage allocation has been exceeded.
The external chunk buffer memory is partitioned into data units called chunks. A chunk is a block
(36 bytes) of contiguous memory used to store parts of the data frames. Associated with each
chunk is an address that is used to index the chunk. The addresses are stored in the external
memory in a free list FIFO. The Free list FIFO contains addresses of all the chunks that are
available for the storage of data. A chunk of data is unavailable when the data stored within the
chunk is part of a datagram that is being actively processed by the FREEDM 84A1024L. Chunks
become available when the FREEDM 84A1024L completes the processing of the data in the
chunk (i.e. the datagram is transferred across the Any-PHY interface to the rest of the system).
Data received from the partial packet RAM is encapsulated (Figure 19). The encapsulation
contains the next address pointer, Last and Full flags, Error codes and an error correction code
that covers the encapsulation header. The next address pointer is used to create a linked list of
chunks that comprise a datagram (Figure 21).The address indicates where the next chunk of the
datagram is located in the external memory. This effectively links the chunks of a datagram in
external memory. The last flag is used to tag the last chunk of a datagram. The full flag indicates
if the chunk contains 32 bytes of data. If the data chunk of a datagram is partially filled, the full
flag is false and the number of valid bytes in the chunk is inserted in byte 0. The error codes are
Small datagrams (shorter than a user-programmable length) are discarded when an excessive
All datagrams received on a particular channel are discarded when the associated Any-PHY
FREEDM 84A1024L ASSP Telecom Standard Product Data Sheet
Released
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