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Once configured, the MU9C8358L will extract the DA
from the frames that are received through the MII ports.
An automatic address processing function is subsequently
triggered. Once the DA processing function is triggered,
the frame is monitored to detect whether it is a broadcast,
multicast, or unicast frame and the appropriate actions are
taken. DA processing consists of the following actions:
Once configured, the MU9C8358L also will perform SA
processing functions after the address information has
been extracted from a received frame. The SA of each
arriving frame is stored by the MU9C8358L for further
processing, along with the ID of the port on which it
arrived, and the current time stamp. Note that at start-up,
permanent addresses and Port IDs are loaded into the
LANCAM through the CPU port; as message traffic
proceeds, new addresses are learned and added to the
LANCAM database, and aged addresses are purged. SA
processing consists of the following actions:
•
•
•
Packets are characterized as Broadcast, Multicast, or
Unicast types.
Unicast packets initiate a search of the CAM for
existing entries.
•
The SA field is collected and temporarily stored. Note
the SA cannot be a Broadcast or Multicast address by
definition.
If a DA match is found, the Port ID read from the
CAM is compared to the Source Port ID. If the Source
Port ID and Destination Port ID match, the frame is
rejected. If the Port IDs are different, the Tag
information is made available for MACs that support
Tag switching, through the Tag port.
•
When the complete packet has arrived, the CRC field
is checked and the length of the packet is checked (if
the CRC facility is enabled and the packet is
10 Base - X). Any errors result in no further SA
processing.
•
•
If the MU9C8358L rejects the frame, it asserts the
Reject output pin (REJ) and forces the MII RX_ER
output (FRX_ER) HIGH for the appropriate MII Port.
This causes the MAC to discard the frame.
•
•
If the packet did not contain any errors (or the CRC
check facility is disabled), the SA field is compared
with the address fields that are stored in the
LANCAM.
Once the DA processing function is complete, the
MU9C8358L stores the result. This result indicates
the characterization of the processed frame.
(Broadcast, Multicast, or Unicast) and the Source Port
ID. Additionally, if a unicast frame was processed, the
result of the search and the port ID of the DA is also
stored. Finally, the detail of whether the Destination
port and the Source port are identical is also stored.
If a match is found, the Port ID and time stamp for
that entry are updated. If no match is found, the SA is
added to the CAM, along with the current time stamp
and the Port ID assigned to that particular Source port.
See the PCFG registers section for more information on
the CRC check facility.
•
The result of DA processing may be read in two ways.
An interrupt may be sent to the host processor
indicating that there is a result available. The host
processor would read the result from an internal
Result Data register. Alternatively, external circuitry
can monitor the status of the Result Port Data valid
(RP_DV) output pin. This output indicates that there
is a result available in the internal register, which can
be read through the Result port. The external circuitry
can read the data by asserting the Result Port Select
(RP_SEL) pin. Assertion of Result Port Next
(RP_NXT) clears the value and advances the next
entry if there is one available.
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MUSIC [ MUSIC SEMICONDUCTORS ]
