LAN9312-NZW Standard Microsystems (SMSC), LAN9312-NZW Datasheet - Page 74

• Manufacturer Part Number: LAN9312-NZW
• Manufacturer: Standard Microsystems (SMSC)

Specifications of LAN9312-NZW

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Revision 1.7 (06-29-10)
6.4.7
6.4.8
Broadcast Throttle Level
Broadcast Storm Control
In addition to ingress rate limiting, the LAN9312 supports hardware broadcast storm control on a per
port basis. This feature is enabled via the
(SWE_BCST_THROT). The allowed rate per port is specified as the number of bytes multiplied by 64
allowed to be received every 1.72 mS interval. Packets that exceed this limit are dropped. Typical
values are listed in
of not limiting the rate.
In addition to the rate limit, the
specifies the maximum number of buffers that can be used by broadcasts, multicasts, and unknown
unicasts.
IPv4 IGMP Support
The LAN9312 provides Internet Group Management Protocol (IGMP) hardware support using two
mechanisms: IGMP monitoring and Multicast Pruning.
On ingress, if IGMP packet monitoring is enabled in the
Register
IGMP monitoring port (typically set to the port to which the host CPU is connected). IGMP packets are
identified as IPv4 packets with a protocol of 2. Both Ethernet and IEEE 802.3 frame formats are
supported as are VLAN tagged packets.
Once the IGMP packets are received by the host CPU, the host software can decide which port or
ports need to be members of the multicast group. This group is then added to the ALR table as detailed
in
IGMP packet if necessary.
Normally, packets are never transmitted back to the receiving port. For IGMP monitoring, this may
optionally be enabled via the
(SWE_GLOBAL_INGRSS_CFG). This function would be used if the monitoring port wished to
participate in the IGMP group without the need to perform special handling in the transmit portion of
the driver software.
Section 6.4.1.3, "Multicast Pruning," on page
252
168
134
(SWE_GLOBAL_INGRSS_CFG), IGMP multicast packets are trapped and redirected to the
67
34
17
8
4
3
2
1
Table
Table 6.4 Typical Broadcast Rate Settings
6.4. When a port is receiving at 10Mbps, any setting above 34 has the effect
High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Buffer Manager Broadcast Buffer Level Register (BM_BCST_LVL)
DATASHEET
Switch Engine Global Ingress Configuration Register
74
64. The host software should also forward the original
Switch Engine Broadcast Throttling Register
Switch Engine Global Ingress Configuration
Bandwidth
900 Kbps
600 Kbps
300 Kbps
2.4 Mbps
1.2 Mbps
75 Mbps
50 Mbps
40 Mbps
20 Mbps
10 Mbps
5 Mbps
SMSC LAN9312
Datasheet