DM9016
3-port switch with Processor Interface
9.2 Switch function:
9.2.1 Address Learning
The DM9016 stores MAC addresses, port
number and time stamp information in the
Hash-based Address Table. The table can learn up to
1K unicast address entries. The DM9016 provides
two methods to learn address in the table,
self-learning and manual learning.
based on DA when incoming packets is UNICAST. If
the DA was not found in address table, the packet is
treated as a multicast packet and forward to other
ports. If the DA was found and its destination port
number is different to source port number, the packet
is forward to destination port.
(3). Switch engine also look up VLAN, Port
Monitor setting and other forwarding constraints for
the forwarding decision, more detail will discuss in
later sections.
Self-learning
The self-learning mechanism means the DM9016
learn the MAC addresses of incoming packets in real
time without CPU’s assistance.
The switch engine creates a new entry if incoming
packet’s Source Address (SA) does not exist and the
packet is valid (error-free). If SA was found and
incoming port mismatch with port number in table,
update the entry with SA and incoming port number.
Those entries will be created, updated or aged
dynamically.
The DM9016 will filter incoming packets under
following conditions:
(1). Error packets, including CRC errors,
alignment errors, illegal size errors.
(2). PAUSE packets.
(3). If incoming packet is UNICAST and its
destination port number is equal to source port
number.
Besides, the DM9016 has an option to disable
address learning for individual port. This feature can
be set by bit 0 of register 65h.
9.2.4 Inter-Packet Gap (IPG)
IPG is the idle time between any two valid packets
at the same port. The typical number is 96 bits time.
In other word, the value is 9.6u sec for 10Mbps and
960n sec for 100Mbps.
Manual Learning
The DM9016 also provides manual learning
mechanism with CPU’s assistance. The CPU can
create, update or delete entry for flexible
management. In addition to above, the entry can be
set as static one that will not be aged-out forever.
9.2.5 Back-off Algorithm
The DM9016 implements the binary exponential
back-off algorithm in half-duplex mode compliant to
IEEE standard 802.3.
9.2.2 Address Aging
The time stamp information of address table is
used in the aging process. The switch engine
updates time stamp whenever the corresponding SA
receives. The switch engine would delete the entry if
its time stamp is not updated for a period of time.
The period can be programmed or disabled through
bit 0 & 1 of register 52h.
9.2.6 Late Collision
Late Collision is a type of collision. If a collision
error occurs after the first 512 bit times of data are
transmitted, the packet is dropped.
9.2.7 Full Duplex Flow Control
The DM9016 supports IEEE standard 802.3x flow
control frames on both transmit and receive sides.
On the receive side, The DM9016 will defer
transmitting next normal frames, if it receives a pause
frame from link partner.
On the transmit side, The DM9016 issues pause
frame with maximum pause time when internal
resources such as received buffers, transmit queue
and transmit descriptor ring are unavailable. Once
9.2.3 Packet Forwarding
The DM9016 forwards the incoming packet
according to following decision:
(1). If DA is Multicast/Broadcast, the packet is
forwarded to all ports, except to the port on which the
packet was received.
(2). Switch engine would look up address table
Preliminarydatasheet
DM9016-13-DS-P01
March 26, 2009
63
DAVICOM [ DAVICOM SEMICONDUCTOR, INC. ]
