LAN9312 datasheet(70/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

Revision 1.2 (04-08-08)

SMSC LAN9312

DATASHEET

6.4.4

VLAN Support

The switch engine supports 16 active VLANs out of a possible 4096. The VLAN table contains the 16

active VLAN entries, each consisting of the VID, the port membership, and un-tagging instructions.

On ingress, if a packet has a VLAN tag containing a valid VID (not 000h or FFFh), the VID table is

searched. If the VID is found, the VLAN is considered active and the membership and un-tag

instruction is used. If the VID is not found, the VLAN is considered foreign and the membership result

is NULL. A NULL membership will result in the packet being filtered if Enable Membership Checking

is set. A NULL membership will also result in the packet being filtered if the destination address is not

found in the ALR table (since the packet would have no destinations).

On ingress, if a packet does not have a VLAN tag or if the VLAN tag contains VID with a value of 0

(priority tag), the packet is assigned a VLAN based on the Port Default VID (PVID) and Priority. The

PVID is then used to access the above VLAN table.

The VLAN membership of the packet is used for ingress and egress checking and for VLAN broadcast

domain containment. The un-tag instructions are used at egress on ports defined as hybrid ports.

Refer to Section 14.5.3.8, on page 376 through Section 14.5.3.11, on page 379 for detailed VLAN

6.4.5

Spanning Tree Support

Hardware support for the Spanning Tree Protocol (STP) and the Rapid Spanning Tree Protocol (RSTP)

includes a per port state register as well as the override bit in the MAC Address Table entries (Section

6.4.1.5, on page 64) and the host CPU port special tagging (Section 6.4.10, on page 75).

The Switch Engine Port State Register (SWE_PORT_STATE) is used to place a port into one of the

modes as shown in Table 6.2. Normally only Port 1 and Port 2 are placed into modes other than

forwarding. Port 0 should normally be left in forwarding mode.

Figure 6.6 VLAN Table Entry Structure

Table 6.2 Spanning Tree States

Port State

Hardware Action

Software Action

01 - Blocking

(also used for

disabled)

Received packets on the port are

discarded.

Transmissions to the port are blocked.

Learning on the port is disabled.

The MAC Address Table should be programmed

with entries that the host CPU needs to receive

(e.g. the BPDU address). The static and override

bits should be set.

The host CPU should not send any packets to the

port in this state.

The host CPU should discard received packets

from this port when in the Disabled state.

Note:

There is no hardware distinction between

the Blocking and Disabled states.

VID

...

Un-tag

MII

Member

MII

Un-tag

Port 1

Member

Port 1

Un-tag

Port 2

Member

Port 2

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