Broadcom BCM5722 - Table 34: Frame Format with 802.1 Q VLAN Tag Inserted

BCM5722 Programmer’s Guide
10/15/07
Broadcom Corporation
Page 69 VLAN Tag Strip Document 5722-PG101-R
VLAN TAG STRIP
Receiving VLAN-tagged (IEEE 802.1q-compliant) packets are automatically supported by the BCM5722 Ethernet controller.
There is no register or setting needed to receive packets that are VLAN-tagged. The VLAN tag is automatically stripped from
the IEEE 802.1q compliant packet at reception and then placed in a receive buffer descriptor’s two byte VLAN tag field. The
flag field has the BD_FLAGS_VLAN_TAG bit set when a valid VLAN packet is received. Once the packet has been serviced
by the host software, these fields should be zeroed out.
In the Receive MAC Mode register (offset 0x468–0x46b), the Keep VLAN Tag Diag Mode bit (bit 10) can be set to force the
BCM5722 Ethernet controller to not strip the VLAN tag from the packet. This is only for diagnostic purposes.
The following table shows the frame format with IEEE 802.1Q VLAN tag inserted.
Table 34: Frame Format with 802.1Q VLAN Tag Inserted
Offset Description
0:5 MAC destination address
6:11 MAC source address
12:13 Tag Protocol ID (TPID)—0x8100
14:15 Tag Control Information (TCI):
• Bit 15:13—IEEE 802.1P priority
• Bit 12—CFI bit
• Bit 11:0—VLAN ID
16:17 The original EtherType
18:1517 Payload