LAN9353 Datasheet, PDF (214/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
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 des-
tination 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 usage of the PVID can be forced by setting the 802.1Q VLAN Disable field in the Switch Engine
Global Ingress Configuration Register (SWE_GLOBAL_INGRSS_CFG), in effect creating port based VLANs.
The VLAN membership of the packet is used for ingress and egress checking and for VLAN broadcast domain contain-
ment. The un-tag instructions are used at egress on ports defined as hybrid ports.
Refer to Section 10.7.3.9, on page 297 through Section 10.7.3.12, on page 302 for detailed VLAN register descriptions.
10.3.5 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 10.3.1.6, on page 208) and the
host CPU port special tagging (Section 10.3.10, on page 220).
The Switch Engine Port State Register (SWE_PORT_STATE) is used to place a port into one of the modes as shown
in Table 10-1. Normally only Port 1 and Port 2 are placed into modes other than forwarding. Port 0, which is connected
to the host CPU, should normally be left in forwarding mode.
TABLE 10-1: SPANNING TREE STATES
Port State
11 - Disabled
01 - Blocking
01 - Listening
Hardware Action
Received packets on the port are
always discarded.
Transmissions to the port are always
blocked.
Learning on the port is disabled.
Received packets on the port are dis-
carded unless overridden.
Transmissions to the port are blocked
unless overridden.
Learning on the port is disabled.
Received packets on the port are dis-
carded unless overridden.
Transmissions to the port are blocked
unless overridden.
Learning on the port is disabled.
Software Action
The host CPU may attempt to send packets to the
port in this state, but they will not be transmitted.
The MAC Address Table should be programmed
with entries that the host CPU needs to receive
(e.g., the BPDU address). The Static and Age 1/
Override bits should be set.
The host CPU may send packets to the port in this
state. Only packets with STP override will be trans-
mitted.
There is no hardware distinction between the Block-
ing and Listening states.
The MAC Address Table should be programmed
with entries that the host CPU needs to receive
(e.g., the BPDU address). The Static and Age 1/
Override bits should be set.
The host CPU may send packets to the port in this
state. Only packets with STP override will be trans-
mitted.
DS00001925A-page 214
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