Register 3: Ethernet MAC Hash Table High (EMACHASHTBLH), offset 0x008
The 64-bit Hash table is used for group address filtering. For hash filtering, the contents of the
Destination Address (DA) in the incoming frame is passed through the CRC logic, and the upper 6
bits of the CRC register are used to index the contents of the Hash table. The most significant bit
determines the register to be used (Ethernet MAC Hash Table High (EMACHASHTBLH) or
Ethernet MAC Hash Table Low (MACHASHTBLL)), and the other five bits determine which bit
within the register. A hash value of 5b'00000 selects bit 0 of the selected register, and a value of
5b'11111 selects bit 31 of the selected register.
The hash value of the destination address is calculated in the following way:
1. Calculate the 32-bit CRC for the DA (See IEEE 802.3, Section 3.2.8 for the steps to calculate
CRC32).
2. Perform bit-wise reversal for the value obtained in Step 1.
3. Take the upper 6 bits from the value obtained in Step 2.
For example, if the DA of the incoming frame is received as 0x1F52419CB6AF, then the internally
calculated 6-bit Hash value is 0x2C and Bit 12 of EMACHASHTBLH register is checked for filtering.
If the DA of the incoming frame is received as 0xA00A98000045, then the calculated 6-bit Hash
value is 0x07 and Bit 7 of Hash Table Low register is checked for filtering.
If the corresponding bit value of the register is 0x1, the frame is accepted. Otherwise, it is rejected.
If the PM (Pass All Multicast) bit is set in the Ethernet MAC Frame Filter (EMACFRAMEFLTR)
register, then all multicast frames are accepted regardless of the multicast hash values.
Ethernet MAC Hash Table High (EMACHASHTBLH)
Base 0x400E.C000
Offset 0x008
Type RW, reset 0x0000.0000
16171819202122232425262728293031
HTH
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
0000000000000000Reset
0123456789101112131415
HTH
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
0000000000000000Reset
DescriptionResetTypeNameBit/Field
Hash Table High
This field contains the upper 32 bits of the hash table.
0x0RWHTH31:0
June 18, 20141482
Texas Instruments-Production Data
Ethernet Controller
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