SMSC LAN9312 - Manual (Page 67)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
SMSC LAN9312 67 Revision 1.4 (08-19-08)
DATASHEET
6.4.3 Transmit Priority Queue Selection
The transmit priority queue may be selected from five options. As shown in Figure 6.4 , the priority may
be based on:
„ the static value for the destination address in the ALR table
„ the precedence bits in the IPv4 TOS octet
„ the DIFFSERV mapping table indexed by the IPv4 TOS octet or the IPv6 Traffic Class octet
„ the VLAN tag priority field using the per port Priority Regeneration table
„ the port default
The last four options listed are sent through the Traffic Class table which maps the selected priority to
one of the four output queues. The static value from the ALR table directly specifies the queue.
Figure 6.4 Switch Engine Transmit Queue Selection
priority
calculation
programmable
DIFFSERV table
programmable
port default
table
programmable
Priority
Regeneration
table
per port
3b
3b
3b
2b
6b
3b
2b
static DA
override
programmable
Traffic Class
table
Packet is Tagged
VL Higher Priority
Packet is IPv 4
Packet is IP
Use Precedence
Use IP
ALR Static Bit
IPv4(TOS)
IPv6(TC)
DA Highest Priority
priority queue
Source Port
ALR Priority
VLAN Priority
IPv4 Precedence 2b
3b
VLAN Enable
Packet is from Host