SLAU723A October 2017 – October 2018 MSP432E401Y , MSP432E411Y
Ethernet MAC VLAN Hash Table (EMACVLANHASH)
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.
EMACVLANHASH is shown in Figure 15-54 and described in Table 15-63.
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| 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| RESERVED | VLHT | ||||||||||||||||||||||||||||||
| R-0x0 | R/W-0x0 | ||||||||||||||||||||||||||||||