TC9205M
Preliminary Data Sheet
7
Broadcast Throttling
In case of excessive broadcast, TC9205M will throttle the broadcast traffic based on buffer memory
loading. Both global buffer pool loading and source port loading are considered. The number of frame
buffers that can be consumed by broadcast packets received from an individual source port is
permanently limited to the EEPROM configurable value (contained by SrcLoadTrsh field from Broadcast
Configuration Register). The default value is 32 when the EEPROM is not present. Additionally,
regarding the global aspect, broadcast frames are always dropped by broadcast queues overflow. Two
broadcast queues are implemented within TC9205M, one for low and normal priority (Classes 0 and 1)
and another for higher priorities (Classes 2 and 3).
Both filtering mechanisms described above can be avoided by enabling the flow control for broadcast
process. This mechanism can be enabled using the FcBcstEn pin shared configuration or by adjusting
the EEPROM setting. In this case the loading thresholds will never be reached and as result no
broadcast packet will be dropped although the filtering mechanism always remains active. If the
broadcast flow control is disabled TC9205M is still capable of taking continuous broadcast frames from
one port and deliver them to all the other ports at maximum speed without losing packets.
Independent of the throttling mechanisms, a bandwidth based broadcast throttling can be enabled using
the BcstThrot pin or by EEPROM setting. When this process is active, the receive broadcast bandwidth
per port will be limited to a value between 1% and 31% from the port’s maximum bandwidth. This
percentage is encoded within ThrotTrsh field from EEPROM's Broadcast Configuration Register. Default
value is 5 (%). Whenever the broadcast traffic bandwidth exceeds the above limit some broadcast
frames will be randomly dropped in order to precisely meet the enforced bandwidth.
TC9205M has the ability to give an indication about its status, from the broadcast packets handling issue
perspective. Its BcstLED pin can signal either if the incoming broadcast packets are dropped or if
broadcast packets overflow a certain threshold. During reset, this pin has the meaning of BcstCfg
shared configuration pin. The BcstLED will behave as a broadcast packets dropping indicator, it lights
periodically whenever a broadcast packet is dropped due to buffer overflow.
8
Port Mirroring
Although TC9205M is a smart switch, it has the ability to set a pair of mirroring ports. This feature is
available only through EEPROM settings. The port mirroring feature can be enabled by setting a value of
‘1’ in either EnTxMirror field from EEPROM’s PortMirrorConfig register or EnRxMirror field from the
same register, or both.
When port-mirroring feature has been enabled, the SourcePort field from EEPROM’s PortMirrorConfig
register selects the monitored port while DestinationPort field from EEPROM’s PortMirrorConfig
register selects the monitoring port. The traffic on the monitored (mirror source) port will be forwarded to
the monitor port (mirror destination). Both ports can be any of the TC9205M’s ports.
If EnRxMirror field is set to ‘1’ then all the incoming traffic of the mirror source port will be simultaneously
forwarded towards its due destination and to the monitoring port. The bad CRC / undersized frames will
be filtered out.
If EnTxMirror field is set to ‘1’ then all the outgoing traffic of the mirror source port will be also forwarded
to the monitoring port.
Confidential.
22/51
July 30, 2003
Copyright © 2003, IC Plus Corp.
TC9205M-DS-R03
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