VIA Technologies, Inc.
Preliminary VT6508 Datasheet
-27-
SRAM size
# of buffers
Max XOFF Min XOFF XON
Rmax
128KB
64
D+C = 29
D = 19
C = 10
D+C = 29
D = 15
C = 10
43
1
256KB
149
4x9+C = 46
C = 10
D+C = 38
D = 28
C = 10
98
4
512KB
320
6x9+C = 76
C = 20
D+C = 57
D = 37
C = 20
198
6
1MB
661
8x9+C=102
C = 30
D+C = 67
D = 37
C = 30
381
8
2.5 BROADCAST STORM FILTERING
In VT6508, the feature of broadcast storm filtering is based on the above congestion
control, and subjects to incoming broadcast packets. When an incoming broadcast packet
is first enqueued by the Input Control of the source port, Queue Control will check if any
one of its destination output ports is in XOFF window. If yes, it will trigger flow control to
source port. For example, if a broadcast packet comes in from port 0, it will be forwarded
to port1, port2, port3, port4, ... port8 in turn. If any one of ports 1~8 is congested, it will
trigger flow control to source port 0, right on it is received and enqueued by Input Control
of port 0.
If any port’s drop window is turned on, Forwarding Control will drop the incoming
broadcast packets to restrict the resource allocation.
2.6 SERIAL EEPROM INTERFACE AND CONFIGURATION COMMANDS
If the chip initialization mode is “EEPROM-init” (by strapping), VT6508 will read the
external EEPROM device through EEC, EEIO during the system initialization
. The signals of
EEPROM interface are described as follows:
Name
Type
Description
EEC
O
serial EEPROM
interface clock
EEIO
IO
serial EEPROM
interface data signal
There are two types of EEPROM commands with the following format:
1. EOF Command: this must be the last command in EEPROM.
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