LAN9353 Datasheet, PDF (224/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
- When a received packet is special-tagged from a CPU port, the special tag is removed.
• CPU Port - Packets transmitted from this port type generally contain a special tag. Special tags are described in
detail in Section 10.3.10, "Host CPU Port Special Tagging," on page 220.
• Hybrid Port - Generally, this port type supports a mix of normal-tagged and non-tagged packets. It is the most
complex, but most flexible port type.
For clarity, the following details the incoming un-tag instruction. As described in Section 10.3.4, "VLAN Support,"
on page 213, the un-tag instruction is the three un-tag bits from the applicable entry in the VLAN table. The entry
in the VLAN table is either the VLAN from the received packet or the ingress port’s default VID.
When a received packet is non-tagged, a new VLAN tag is added if two conditions are met. First, the Insert Tag bit
for the egress port in the Buffer Manager Egress Port Type Register (BM_EGRSS_PORT_TYPE) must be set.
Second, the un-tag bit, for the egress port, from the un-tag instruction associated with the ingress port’s default
VID, must be cleared. The VLAN tag that is added will have a VID taken from either the ingress or egress port’s
default VID. The priority of the VLAN tag is either the priority calculated on ingress or the egress port’s default. The
choice of ingress or egress is determined by the egress port’s VID/Priority Select bit in the Buffer Manager Egress
Port Type Register (BM_EGRSS_PORT_TYPE).
When a received packet is priority-tagged, either the tag is removed or it is modified. If the un-tag bit, for the
egress port, from the un-tag instruction associated with the ingress port’s default VID is set, then the tag is
removed. Otherwise, the tag is modified. The VID of the new VLAN tag is changed to either the ingress or egress
port’s default VID. If the Change Priority bit in the Buffer Manager Egress Port Type Register
(BM_EGRSS_PORT_TYPE) for the egress port is set, then the Priority field of the new VLAN tag is also changed.
The priority of the VLAN tag is either the priority calculated on ingress or the egress port’s default. The choice of
ingress or egress is determined by the egress port’s VID/Priority Select bit.
When a received packet is normal-tagged, either the tag is removed, modified or passed unchanged. If the un-tag
bit, for the egress port, from the un-tag instruction associated with the VID in the received packet is set, then the
tag is removed. Else, if the Change Tag bit in the Buffer Manager Egress Port Type Register
(BM_EGRSS_PORT_TYPE) for the egress port is clear, the packet passes untouched. Else, if both the Change
VLAN ID and the Change Priority bits in the Buffer Manager Egress Port Type Register (BM_EGRSS_PORT_-
TYPE) for the egress port are clear, the packet passes untouched. Otherwise, the tag is modified. If the Change
VLAN ID bit for the egress port is set, the VID of the new VLAN tag is changed to either the ingress or egress
port’s default VID. If the Change Priority bit for the egress port is set, the Priority field of the new VLAN tag is
changed to either the priority calculated on ingress or the egress port’s default. The choice of ingress or egress is
determined by the egress port’s VID / Priority Select bit.
When a packet is received special-tagged from a CPU port, the special tag is removed.
DS00001925A-page 224
 2015 Microchip Technology Inc.