DM8203
2-port switch with MII / RMII Interface
programmed by EEPROM or register 67h, the default
setting is no broadcast storm protecting.
9.2.9 Partition Mode
The DM8203 provides a partition mode for each
port, see bit 6 of register 61h. The port enters
partition mode when more than 64 consecutive
collisions are occurred. In partition mode the port
continuous to transmit but it will not receive. The port
returned to normal operation mode when a good
packet is seen on the wire. The detail description of
partition mode represent following:
9.2.11 Bandwidth Control
The DM8203 supports two types of bandwidth
control for each port. One is the ingress and egress
bandwidth rate can be controlled separately, the
other is combined together, this function can be set
through bit 3 of register 61h. The bandwidth control is
disabled by default.
(1). Entering Partition State
A port will enter the Partition State when either of
the following conditions occurs:
z The port detects a collision on every one of 64
consecutive re-transmit attempts to the same packet.
z The port detects a single collision which occurs
for more than 512 bit times.
To separate bandwidth control mode, the
threshold rate is defined in register 66h. For
combined mode, it is defined in register 67h.
The behavior of bandwidth control as below:
(1).For the ingress control, if flow control function
is enabled, Pause or Jam packet will be transmitted.
The ingress packets will be dropped if flow control is
disabled.
z Transmit defer timer time out, which indicates
the transmitting packet is deferred to long.
(2).For the egress control, the egress port will not
transmit any packets. On the other hand, the ingress
bandwidth of source port will be throttled that prevent
packets from forwarding.
(3).In combined mode, if the sum of ingress and
egress bandwidth over threshold, the bandwidth will
be throttled.
(2). While in Partition state:
The port will continue to transmit its pending
packet, regardless of the collision detection, and will
not allow the usual Back-off Algorithm. Additional
packets pending for transmission will be transmitted,
while ignoring the internal collision indication. This
frees up the ports transmit buffers which would
otherwise be filled up at the expense of other ports
buffers. The assumption is that the partition is
9.2.12 Port Monitoring Support
The DM8203 supports “Port Monitoring” function
on per port base, detail as below:
signifying
a
system failure situation (bad
connection/cable/station), thus dropping packets is a
small price to pay vs. the cost of halting the switch
due to a buffer full condition.
(1). Sniffer Port and Monitor Port
There is only one port can be selected as “sniffer
port” by register 52h, multiple ports can be set as
“receive monitor port” or “transmit monitor port” in
per-port register 65h.
(3). Exiting from Partition State
The Port exits from Partition State, following the
end of a successful packet transmission.
successful packet transmission is defined as no
collisions were detected on the first 512 bits of the
transmission.
(2).Receive monitor
A
All packets received on the “receive monitor port”
are send a copy to “sniffer port”. For example, port 0
is set as “receive monitor port” and port 2 is selected
as a “sniffer port”. If a packet is received form port 0
and predestined to port 1 after forwarding decision,
the DM8203 will forward it to port 1 and port 2 in the
end.
9.2.10 Broadcast Storm Filtering
The DM8203 has an option to limit the traffic of
broadcast or multicast packets, to protect the switch
from lower bandwidth availability.
There are two types of broadcast storm control,
one is throttling broadcast packet only, the other
includes multicast. This feature can be set through bit
1 of register 61h.
(3).Transmit monitor
All packets transmitted on the “transmit monitor
port” are send a copy to “sniffer port”. For example,
port 1 is set as “transmit monitor port” and port 2 is
selected as “sniffer port”. If a packet is received from
port 0 and predestined to port 1 after forwarding
decision, the DM8203 will forward it to port 1 and port
The broadcast storm threshold can be
Preliminarydatasheet
DM8203-15-DS-P05
October 23, 2008
45
DAVICOM [ DAVICOM SEMICONDUCTOR, INC. ]
