LAN9353 Datasheet, PDF (220/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
Normally, packets are never transmitted back to the receiving port. For IGMP/MLD monitoring, this may optionally be
enabled via the Allow Monitor Echo field in the Switch Engine Global Ingress Configuration Register (SWE_-
GLOBAL_INGRSS_CFG). This function would be used if the monitoring port wished to participate in the IGMP/MLD
group without the need to perform special handling in the transmit portion of the driver software.
Note: Most forwarding rules are skipped when a packet is monitored. However, a packet is still filtered if:
• The source port is in the Disabled state.
• The source port is in the Learning or Listening / Blocking state (unless Spanning Tree Port State Override is in
effect.
• VLANs are enabled, the packet is untagged or priority tagged and the Admit Only VLAN bit for the ingress port is
set.
• VLANs are enabled and the packet is tagged and had a VID equal to FFFh.
• VLANs are enabled, Enable Membership Checking on Ingress is set, Admit Non Member is cleared and the
source port is not a member of the incoming VLAN.
10.3.9 PORT MIRRORING
The device supports port mirroring where packets received or transmitted on a port or ports can also be copied onto
another “sniffer” port.
Port mirroring is configured using the Switch Engine Port Mirroring Register (SWE_PORT_MIRROR). Multiple mirrored
ports can be defined, but only one sniffer port can be defined.
When receive mirroring is enabled via the Enable RX Mirroring field, packets that are forwarded from a port designated
as a Mirrored Port are also transmitted by the Sniffer Port. For example, Port 2 is setup to be a mirrored port and Port
0 is setup to be the sniffer port. If a packet is received on Port 2 with a destination of Port 1, it is forwarded to both Port
1 and Port 0.
When transmit mirroring is enabled via the Enable TX Mirroring field, packets that are forwarded to a port designated
as a Mirrored Port are also transmitted by the Sniffer Port. For example, Port 2 is setup to be a mirrored port and Port
0 is setup to be the sniffer port. If a packet is received on Port 1 with a destination of Port 2, it is forwarded to both Port
2 and Port 0.
A packet will never be transmitted out of the receiving port. A receive packet is not normally mirrored if it is filtered. This
can optionally be enabled via the Enable RX Mirroring Filtered field.
10.3.10 HOST CPU PORT SPECIAL TAGGING
The Switch Engine Ingress Port Type Register (SWE_INGRSS_PORT_TYP) and the Buffer Manager Egress Port Type
Register (BM_EGRSS_PORT_TYPE) are used to enable a special VLAN tag that is used by the host CPU. This special
tag is used to specify the port(s) where packets from the CPU should be sent and to indicate which port received the
packet that was forwarded to the CPU.
10.3.10.1 Packets from the Host CPU
The Switch Engine Ingress Port Type Register (SWE_INGRSS_PORT_TYP) configures the switch to use the special
VLAN tag in packets from the host CPU as a destination port indicator. A setting of 11b should be used on the port that
is connected to the host CPU (typically Port 0). A setting of 00b should be used on the normal network ports.
The special VLAN tag is a normal VLAN tag where the VID field is used as the destination port indicator.
VID bit 3 indicates a request for an ALR lookup.
If VID bit 3 is zero, then bits 0 and 1 specify the destination port (0, 1, 2) or broadcast (3). Bit 4 is used to specify if the
STP port state should be overridden. When set, the packet will be transmitted, even if the destination port(s) is (are) in
the Learning or Listening / Blocking state.
If VID bit 3 is one, then the normal ALR lookup is performed and learning is performed on the source address (if enabled
in the Switch Engine Port Ingress Configuration Register (SWE_PORT_INGRSS_CFG) and the port state for the CPU
port is set to Forwarding or Learning). The STP port state override is taken from the ALR entry.
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 10.3.3,
"Transmit Priority Queue Selection," on page 210 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.
DS00001925A-page 220
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