Texas Instruments TMS320C645x DSP - Manual (Page 123)

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5.37 MAC Hash Address Register 1 (MACHASH1)
EMAC Port Registers
The MAC hash registers allow group addressed frames to be accepted on the basis of a hash function of
the address. The hash function creates a 6-bit data value (hash_fun) from the 48-bit destination address
(DA) as follows:
Hash_fun(0)=DA(0) XOR DA(6) XOR DA(12) XOR DA(18) XOR DA(24) XOR DA(30) XOR DA(36) XOR DA(42);
Hash_fun(1)=DA(1) XOR DA(7) XOR DA(13) XOR DA(19) XOR DA(25) XOR DA(31) XOR DA(37) XOR DA(43);
Hash_fun(2)=DA(2) XOR DA(8) XOR DA(14) XOR DA(20) XOR DA(26) XOR DA(32) XOR DA(38) XOR DA(44);
Hash_fun(3)=DA(3) XOR DA(9) XOR DA(15) XOR DA(21) XOR DA(27) XOR DA(33) XOR DA(39) XOR DA(45);
Hash_fun(4)=DA(4) XOR DA(10) XOR DA(16) XOR DA(22) XOR DA(28) XOR DA(34) XOR DA(40) XOR DA(46);
Hash_fun(5)=DA(5) XOR DA(11) XOR DA(17) XOR DA(23) XOR DA(29) XOR DA(35) XOR DA(41) XOR DA(47);
This function is used as an offset into a 64-bit hash table stored in MACHASH1 and MACHASH2 that
indicates whether a particular address should be accepted or not.
The MAC hash address register 1 (MACHASH1) is shown in Figure 65 and described in Table 65 .
Figure 65. MAC Hash Address Register 1 (MACHASH1)
31 16
MACHASH1
R/W-0
15 0
MACHASH1
R/W-0
LEGEND: R/W = Read/Write; -n = value after reset
Table 65. MAC Hash Address Register 1 (MACHASH1) Field Descriptions
Bit Field Value Description
31-0 MACHASH1 Least-significant 32 bits of the hash table corresponding to hash values 0 to 31. If a hash table bit is
set, then a group address that hashes to that bit index is accepted.
SPRU975B – August 2006 Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO) 123
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