PM7312 pmc-sierra, PM7312 Datasheet - Page 70

• Manufacturer Part Number: PM7312
• Description: Freedm 32a1024l Assp Telecom Standard Datasheet
• Manufacturer: pmc-sierra

Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2021833, Issue 2
the system via the Any-PHY interface enabling the system to observe the behavior of the HDLC
channels.
The Partial packet RAM also passes the associated HDLC channel ID, End of datagram indication,
and error flags (Bad FCS, Abort, etc.). The HDLC channel ID is used to index a data record that
provides the next chunk pointer. This data record is also used to store frame relay header bits
(Sequence number, DLCI, BE, FE, DE, B, E, C) or PPP header bits (Address, Control, PID, COS,
and Sequence number, B, E), and the address of the first chunk in the datagram. These header fields
are passed to the frame builder after the last chunk in a given datagram is stored. Header bits are
extracted from the first data chunk of a datagram. Corrupted datagrams are tagged and the starting
address is passed forward to the re-sequencer.
The RFRAG can be configured to accept compressed PPP headers. The RFRAG will correctly
interpret the compressed header, and extract the information required for downstream processing
from the packet.
The encapsulated data chunk, and an address pointer are passed to the DRAMC controller for
storage in external SDRAM. The address pointer is contained in the HDLC channel record and
points to the memory location that is placed in the next address pointer field of the previous data
chunk for a given datagram. The initial chunk of a datagram is stored at an address location,
(starting address of the datagram).
Datagrams may also be discarded before they are stored in the external SDRAM. When there are
too many datagrams waiting to be processed by the re-sequencer, any datagram smaller than either
a default 40-byte limit, or a programmable 0 to 56-byte threshold, will be discarded, except if it is
tagged as the last fragment of a multi-fragment frame/packet. Furthermore, each Any-PHY channel
has a limit in the maximum number of chunks that it can have stored in the external SDRAM at any
time. If this limit is exceeded, all datagrams for this Any-PHY channel will be discarded until the
number of chunks stored in the external SDRAM is reduced below the limit.
The free list FIFO is stored in external memory. To reduce the accesses to external memory, an
address cache is used to hold addresses that can be used for next pointer values. When a chunk is
encapsulated, the HDLC channel record will fetch, from the local cache, an address that can serve
as the next address for the following data chunk in the datagram. As chunks are retrieved from the
external memory for the address is returned to the cache. When the cache needs to be replenished,
a request is made to the DRAMC. A set of new addresses is provided from external memory. The
external read request is triggered off of a threshold. When the internal Cache crosses the threshold,
it requests a read from external memory.
Figure 19 Encapsulated Chunk Structures (Full = True)
Byte 1
Byte 7
Byte 13
Byte 19
Byte 25
Byte 31
Byte 0
Byte 6
Byte 12
Byte 18
Byte 24
Byte 30
Byte 5
Byte 11
Byte 17
Byte 23
Byte 29
ECC(8)
FREEDM 32A1024L ASSP Telecom Standard Product Data Sheet
L
Byte 4
Byte 10
Byte 16
Byte 22
Byte 28
F
EC(3)
NXT_CHUNK_PTR(19)
Byte 3
Byte 9
Byte 15
Byte 21
Byte 27
Byte 2
Byte 8
Byte 14
Byte 20
Byte 26
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