Revisions Affected

0, A

Details

The ETV, DOVLTC, and ERSVLM bits of the MAC_VLAN_Tag_Data register accessed via the MAC_VLAN_Tag_Ctrl register (Extended Receive VLAN filtering is selected) are used to program the mode of operation of the Receive VLAN Hash Filtering. The ETV bit is used to enable computation of Hash for only 12 bits of VLAN Tag. The DOVLTC bit is used to disable VLAN Type Check for VLAN Hash filtering. The ERSVLM bit is used to enable VLAN Hash filtering for S-VLAN Type. However, due to this defect, the Receive VLAN Hash filter always operates in default mode; that is, VLAN Hash is always computed for 16-bits (ETV = 0) of C-VLAN Tag (DOVLTC = 0 and ERSVLM = 0). Therefore, programming the ETV, DOVLTC, or ERSVLM bits to 1 has no effect because these bits have an incorrect read-only attribute. As a result, unintended packets might be forwarded to the application due to an incorrect filter pass or bypass results/status. Also, packets might be dropped in the MAC due to an incorrect filter fail result.

The defect is applicable when non-default VLAN Hash filtering modes are programmed; that is, one or more of the ETV, DOVLTC, and ERSVLM bits are set to 1.

Workaround

The software should disable the Receive VLAN Hash filtering by setting the VTHM bit of the MAC_VLAN_Tag_Ctrl register to 0 (when non-default VLAN Hash filtering mode is required) and use the alternative filtering methods available in the hardware (perfect or inverse VLAN filtering), or perform filtering in software.

Use only the default VLAN Hash filtering modes.