LAN9303 datasheet(79/366 Pages) SMSC

79 / 366 page

Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII

Datasheet

SMSC LAN9303/LAN9303i

Revision 1.3 (08-27-09)

DATASHEET

6.4.7

Broadcast Storm Control

In addition to ingress rate limiting, the device supports hardware broadcast storm control on a per port

basis. This feature is enabled via the Switch Engine Broadcast Throttling Register

(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 Table 6.4. When a port is receiving at 10Mbps, any setting above 34 has the effect

of not limiting the rate.

In addition to the rate limit, the Buffer Manager Broadcast Buffer Level Register (BM_BCST_LVL)

specifies the maximum number of buffers that can be used by broadcasts, multicasts, and unknown

unicasts.

6.4.8

IPv4 IGMP Support

The device 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 Switch Engine Global Ingress Configuration

IGMP monitor 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 Section 6.4.1.3, "Multicast Pruning," on page 68. The host software should also forward the original

IGMP packet if necessary.

Normally, packets are never transmitted back to the receiving port. For IGMP monitoring, this may

optionally be enabled via 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 group without the need to perform special handling in the transmit portion of

the driver software.

Table 6.4 Typical Broadcast Rate Settings

Broadcast Throttle Level

Bandwidth

252

75 Mbps

168

50 Mbps

134

40 Mbps

20 Mbps

10 Mbps

5 Mbps

82.4 Mbps

41.2 Mbps

900 Kbps

600 Kbps

300 Kbps

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