Register 37: Ethernet MAC VLAN Hash Table (EMACVLANHASH), offset 0x588
The 16-bit hash table is used for group address filtering based on VLAN tag when the VTHM bit of
the EMACVLANTG register is set. For hash filtering, the content of the 16-bit VLAN tag or 12-bit
VLAN ID (enabled by ETV in the EMACVLANTG register) in the incoming frame is passed through
the CRC logic and the upper four bits of the calculated CRC are used to index the contents of the
EMACVLANHASH register. For example, a hash value of 0x8 selects bit 8 of the VLAN Hash table.
The hash value of the destination address is calculated in the following way:
1. Calculate the 32-bit CRC for the VLAN tag or ID (See IEEE 802.3, Section 3.2.8 for the steps to
calculate CRC32).
2. Perform bitwise reversal for the value obtained in Step 1.
3. Take the upper four bits from the value obtained in Step 2.
If the corresponding bit value of the register is 0x1, the frame is accepted. Otherwise, it is rejected.
Ethernet MAC VLAN Hash Table (EMACVLANHASH)
Base 0x400E.C000
Offset 0x588
Type RW, reset 0x0000.0000
16171819202122232425262728293031
reserved
ROROROROROROROROROROROROROROROROType
0000000000000000Reset
0123456789101112131415
VLHT
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
0000000000000000Reset
DescriptionResetTypeNameBit/Field
Software should not rely on the value of a reserved bit. To provide
compatibility with future products, the value of a reserved bit should be
preserved across a read-modify-write operation.
0x0ROreserved31:16
VLAN Hash Table
This field contains the 16-bit VLAN Hash Table.
0x0RWVLHT15:0
1533June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller
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