VT6516 datasheet(34/73 Pages) ETC

34 / 73 page

VIA Technologies, Inc.

Preliminary VT6516 Datarsheet

-34-

When request transfer to or from SDRAM through scheduler, the input control need to derive each burst

starting address to bank0 or bank1 information for scheduler to utilize SDRAM bandwidth efficiently. When

input FIFO is filled to 12x64 or page boundary or end of frame, the input port control will request DRAM access

to write packet. Input FIFO size is 64 bits by 24.

After receiving the grant of queueing (cut-through or store-and-forward), even the bad packet has to be

forwarded.

While cut-through, the input control will request the grant of cut-through counter bus for passing the cut

through packet count from input port to output port as the whole packet has received.

4.2.1 Cross VLAN Server Port support

The VT6516 support Cross VLAN server port configuration, the following illation show the sample of

server ports configuration by set the register of server port mask(14A0H~14A1H), and server ports only enable

after the VLAN enabled. The multicast or broadcast frames received from one VLAN group will forward to any

server ports and only forward to the ports with same VID.

4.3 Network Management Features

Flow control

The flow control activity is triggered when the buffer utilization exceeds certain thresholds specified by

the dedicated register XXXX, Register-XXXX is used to specify the upper and lower thresholds of reserved

buffer slot for whole switch.

Under full-duplex mode operation, if the buffer utilization of whole switch has exceeded the upper

threshold and the permanent buffer has been used up, a flow control with a predefined pause time value will

be sent to the source port to stop the input traffic. If flow control mechanism is not enabled, the public buffer

will exhausted so that the further incoming frames will be dropped.

Under half duplex operation, if the buffer utilization of whole switch has exceeded the upper threshold

and the permanent buffer has been used up, the port will perform back-pressure based flow control by

sending a jam pattern on each incoming frame. If backpressure flow control of the port is not enable, the

frame will be dropped.

Sniffer port

The VT6516 support sniffer function for user to monitor the network traffic. The Sniffer port enable can

be set for any individual port of sixteen ports. And each sniffer port can set to monitor the traffic coming

from any others fifteen port(monitor port). Any packets sent to the monitor ports or transmitted out of

monitor port will be forwarded to sniffer port.

Spanning tree support

The VT6516 support the spanning tree protocol (STP). When spanning tree protocol support is enabled,

frames from the CPU port having a DA value equal to reserved Bridge Management Group Address for

BPDU will be forwarded to the port specified by the CPU. Frames from other port with a DA equal to

reserved Bridge Management Group Address for BPDU will be forwarded to the CPU port.

VT6516 Datasheet(PDF) 34 Page - List of Unclassifed Manufacturers