LAN9303 Datasheet, PDF (81/366 Pages) SMSC Corporation – Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII

Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII
Datasheet
VID bit 5 indicates a request to calculate the packet priority (and egress queue) based on the packet
contents.
If VID bit 5 is zero, the PRI field from the VLAN tag is used as the packet priority.
If VID bit 5 is one, the packet priority is calculated from the packet contents. The procedure described
in Section 6.4.3, "Transmit Priority Queue Selection," on page 71 is followed with the exception that
the special tag is skipped and the VLAN priority is taken from the second VLAN tag, if it exists.
VID bit 6 indicates a request to follow VLAN rules.
If VID bit 6 is zero, a default membership of “all ports” is assumed and no VLAN rules are followed.
If VID bit 6 is one, all ingress and egress VLAN rules are followed. The procedure described in Section
6.4.2, "Forwarding Rules," on page 70 is followed with the exception that the special tag is skipped
and the VID is taken from the second VLAN tag if it exists.
Upon egress from the destination port(s), the special tag is removed. If a regular VLAN tag needs to
be sent as part of the packet, then it should be part of the packet data from the host CPU port or set
as an unused bit in the VID field.
Note:
When specifying Port 0 as the destination port, the VID will be set to 0. A VID of 0 is normally
considered a priority tagged packet. Such a packet will be filtered if Admit Only VLAN is set
on the host CPU port. Either avoid setting Admit Only VLAN on the host CPU port or set an
unused bit in the VID field.
Note:
The maximum size tagged packet that can normally be sent into a switch port (on port 0) is
1522 bytes. Since the special tag consumes four bytes of the packet length, the outgoing
packet is limited to 1518 bytes, even if it contains a regular VLAN tag as part of the packet
data. If a larger outgoing packet is required, the Jumbo2K bit in the Port x MAC Receive
Configuration Register (MAC_RX_CFG_x) of Port 0 should be set.
6.4.10.2
Packets to the Host CPU
The Buffer Manager Egress Port Type Register (BM_EGRSS_PORT_TYPE) configures the switch to
add the special VLAN tag in packets to the host CPU as a source port indicator. A setting of 11b should
be used only on the port that is connected to the host CPU (typically Port 0). Other settings can be
used on the normal network ports as needed.
The special VLAN tag is a normal VLAN tag where:
„ The priority field indicates the packet’s priority as classified on receive.
„ Bits 0 and 1 of the VID field specify the source port (0, 1, or 2).
„ Bit 3 of the VID field indicates the packet was a monitored IGMP packet.
„ Bit 4 of the VID field indicates STP override was set (static AND age bits set) in the ALR entry for
the packet’s Destination MAC Address.
„ Bit 5 of the VID field indicates the static bit was set in the ALR entry for the packet’s Destination
MAC address.
„ Bit 6 of the VID field indicates priority enable was set in the ALR entry or the packet’s Destination
MAC address.
„ Bits 7,8, and 9 of the VID field are the priority field in the ALR entry for the packet’s Destination
MAC address - these can be used as a tag to identify different packet types (PTP, RSTP, etc.) when
the host CPU adds MAC address entries.
Note: Bits 4 through 9 of the VID field will be all zero for Destination MAC Addresses that have been
learned (i.e., not added by the host) or are not found in the ALR table (i.e., not learned or
added by the host).
Upon egress from the host CPU port, the special tag is added. If a regular VLAN tag already exists,
it is not deleted. Instead it will follow the special tag.
SMSC LAN9303/LAN9303i
81
DATASHEET
Revision 1.3 (08-27-09)