TC9208M
Preliminary Data Sheet
6
Trunk Configuration
TC9208M can setup two port aggregation links, named ‘Trunk A’. Using this feature multiple TC9208M
can be cascaded or interconnected with other switches supporting the trunking feature.
The trunks can be independently configured according with tables below using shared configuration pins
or configuring EEPROM settings. Trunk channel A is comprised from ports 0 and 1,. The traffic on the
ports of the same trunk will be automatically balanced. TC9208M can select from three balancing
methods based on source port, source address and destination address fields within the packet as
shown in the table below, using TnkMod0, TnkMod1 shared configuration pins or EEPROM.
Configuration
Pins Latched
Description
TrunkA
TxData2_7
Enable/disable the trunk channel A.
'0' – Trunk A is disabled
'1' – Trunk A is enabled
TnkMod[1:0]
TxData2_[5:4] Sets the balancing method for loading the two ports within the same
trunk channel.
'00' – Sets the source port based method
'01' – Sets the source address based method
'10' – Sets the source and destination addresses based method
'11' – not used
Different stations connected on the same port may not send traffic on the same trunk line. The frame
order is guaranteed for source port based method and source address based method for all frame
types. If the source and destination addresses based method is used a better balancing may be
achieved but the broadcast frames might be misordered with respect to unicast frames from the same
source address.
If ports within the trunk channel are configured as 10/100 Mbps ports, it is recommended to operate them
in full duplex and with the same speed. Interconnection port order is not mandatory. If one port within the
trunk experience link failure, TC9208M will redistribute the whole traffic to the other remaining trunk port.
7
Flow Control
Whenever the memory load exceeds preset thresholds flow control commands are issued by the traffic
management entity to the transmit MACs to prevent overflow conditions occurred. The overrun conditions
are either locally or globally triggered, depending on the traffic management entity configuration. Transmit
MAC executed those flow control commands depending on the duplex mode status. TC9204M executes
backpressure for half duplex operation mode and it is IEEE 802.3x compliant for full duplex operation mode.
In special conditions forward-pressure is also executed to eliminate packet loss.
For full duplex operation mode, TC9208M applies the XON/XOFF method using IEEE 802.3x PAUSE
frames. When a flow control command is internally generated, the transmit MAC inserts a pause frame
immediately or after the current transmission ends. On the receiving side, if a flow control frame is received,
the transmit MAC will stop transmission for a number of slot times, where the pausing time was extracted
from the received pause frame. The flow control function of the receiving side is always operational unless is
specifically disabled by EEPROM on a per port basis (if no EEPROM is present the receive side flowcontrol
is always operational), while transmission of the pause frames obeys the auto negotiation result.
TC9208M recognizes flow control frames from the incoming frames and these frames should also have a
valid CRC. The IEEE 802.3x PAUSE operation reserved destination address, MAC control type and
PAUSE opcode (88-08-00-01). The chip filters all frames having PAUSE operation reserved DA
disregarding the other fields. If enabled, direct flow control addressing can be executed. This implies
inserting the port address as SA in each flow control frame generated by TC9208M and recognizing as
flow control all received frames with the port’s address as DA, MAC control type and PAUSE opcode.
Confidential.
22/53
August 1, 2003
Copyright © 2003, IC Plus Corp.
TC9208M-DS-R06
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