VLAN Support

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

Document ID
UG1085
Release Date
2022-09-15
Revision
2.3 English

An Ethernet encoded IEEE Std 802.1Q VLAN tag is shown in Table: Ethernet Encoded IEEE Std 802.1Q VLAN Tag.

Table 34-4:      Ethernet Encoded IEEE Std 802.1Q VLAN Tag

16-bit Tag Protocol Identifier (TPID)

16-bit Tag Control Information (TCI)

0x8100

First 3 bits priority, then CFI bit, last 12 bits VID

The VLAN tag is inserted at the 13th byte of the frame adding an extra four bytes to the frame. To support these extra four bytes, the gigabit Ethernet controller can accept frame lengths up to 1,536 bytes by setting bit [8] in the network configuration register.

If the VLAN identifier (VID) is null (0x000) a priority-tagged frame is indicated.

The following bits in the receive buffer descriptor status word provide information about VLAN tagged frames.

Set bit [21] if the receive frame is VLAN tagged (that is, type ID of 0x8100).

Set bit [20] if receive frame is priority tagged (that is, type ID of 0x8100 and null VID). If bit [20] is set, bit [21] is also set.

Set bits [19], [18], and [17] to priority if the bit [21] is set.

Set bit [16] to CFI if bit [21] is set.

The controller can be configured to reject all frames except VLAN tagged frames by setting the discard non-VLAN frames bit in the network configuration register.