MU9C8338A 10/100Mb Ethernet Filter Interface
Functional Description
Destination Address Processing
Once configured, the MU9C8338A will extract the DA
from the frames that are received through the MII port. 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:
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Packets are characterized as Broadcast, Multicast, or
Unicast types.
Unicast packets initiate a search of the CAM for
existing entries.
Multicast and Broadcast packets will also initiate a
search if the PCFG_EXT register is appropriately
configured.
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.
If a DA match is not found and the packet
characterized as Multicast or Broadcast, a default
action is carried out if Multicast Processing is
enabled. This allows Multicast and Broadcast packets
to be processed appropriately and is configured in the
PCFG_EXT register.
If the MU9C8338A rejects the frame, it asserts the
Reject output pin (REJ) and forces the MII RX_ER
output (FRX_ER) HIGH for the MII Port. This causes
the MAC to discard the frame.
Once the DA processing function is complete, the
MU9C8338A 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.
The result of DA processing may be read in two ways.
1. 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.
2. 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.
Source Address Processing
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Once configured, the MU9C8338A 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 MU9C8338A for further
processing, along with the port ID and the current time
stamp. Note that at start-up, permanent addresses and their
Port ID 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:
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The SA field is collected and temporarily stored. Note
the SA cannot be a Broadcast or Multicast address by
definition.
When the complete packet has arrived, the CRC field
is checked and the length of the packet is checked.
Any errors result in no further SA processing.
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.
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.
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Rev. 0a
MUSIC [ MUSIC SEMICONDUCTORS ]
