DM8108
8 port 10/100M Fast Ethernet Switching Controller
Preliminary
11
Version: DM8108-DS-P02
November 25, 1999
Packet Routing
As any port in the DM8108 receives a packet, the DM8108
will put the received data in the receiving buffer and start the
address recognition at same time.
1.
If the destination address is pointed to a local port
other than receiving port, the DM8108 will update the
Transmit Descriptor of the target port with the buffer
location and byte count information and wait for
transmission.
2.
If the destination address is pointed to a port located in
other devices, the DM8108 will update the
Transmit Descriptor of the expansion port with the
receiving buffer location and byte count information
and wait for transmission.
3.
I
f the destination address is not found in the Address
Table, the DM8108 will update all the Transmit
Descriptors, except the one of the receiving port, for
transmission.
4.
For the Multicast/Broadcast addresses, the DM8108
simply updates all the Transmit Descriptors, except
the one of the receiving port or the ports that are
disabled, for Transmission.
5.
For bad packet, the DM8108 simply discards it.
6.
If the receiving buffer or the Transmit Descriptor for a
particular port is full, the packet will be lost.
Network Management Features
The DM8108 is targeted for the non-managed Ethernet
Switching application. No management functions provided.
DRAM Interface
The DM8108 interfaces to 1M or 2M bytes of SGRAM or
SDRAM. The DRAM is used to store incoming packets as
well as he address table and Transmit Descriptors. The
DRAM can operate at up to 90MHz. One 256kx32 or
512kx16 SGRAM are required respectively for 1M or 2M
shared memory size.
Expansion Bus
The expansion bus contains Receive Port and Transmit
Port. Each port is 4-bit wide.
The Receive Port takes the incoming packet into a FIFO
that has to be distributed to the Receiving Buffer
immediately. At the same time, the DM8108 will check the
destination and source addresses to determine the target
port and update the Address Table if necessary.
The Transmit Port is dedicated for transferring packets out
to other switching members if the Transmit Descriptor for
this port saying the transmission is pending.
Total of 8-DM8108 can be cascaded for a 64-port switching
system.
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