Ethernet MAC Register Definitions
8-72
ADSP-BF537 Blackfin Processor Hardware Reference
EMAC_HASHLO and EMAC_HASHHI Registers
The
EMAC_HASHLO
register holds the values for bins 31–0 of the multicast
hash table. The
EMAC_HASHHI
register holds the values for bins 63–32 of
and
The 64-bit multicast table is used for multicast frame address filtering. A
cyclic redundancy check (CRC) based hash table scheme is used. After the
destination address (6th byte) of the frame is received, the state of the
CRC-32 checksum unit is sampled. This CRC-32 unit implements the
IEEE 802.3 CRC algorithm used in validating the FCS field of the frame.
The 6 most significant bits from this state identify one of 64 hash bins
representing the frame’s destination address. These 6 bits are then used to
index into the two hash table registers and extract the corresponding hash
bin enable bit. The most significant bit of this value determines the regis-
ter to be used (high/low) while the other five bits determine the bit
position within the register. A CRC value of 000000 selects bit 0 of the
MAC multicast hash table low register and a CRC value of 111111 selects
bit 31 of the MAC multicast hash table high register.
If the corresponding bit in the hash table register is set, the multicast
frame is accepted. Otherwise, it is rejected. If the
PM
bit in the
EMAC_OPMODE
register is set, all multicast frames are accepted regardless of
the hash values.
For example, consider the calculation of the hash bin for the MAC address
01.23.45.67.89.AB. The CRC algorithm uses an LFSR with the prime
generator polynomial specified in IEEE 802.3 Sec 3.2.8:
G(x) = x
32
+ x
26
+ x
23
+ x
22
+ x
16
+ x
12
+ x
11
+ x
10
+ x
8
+ x
7
+ x
5
+ x
4
+ x
2
+ x + 1
The bits of the MAC address are fed in leftmost byte first, least significant
bit first, in this sequence (left to right):
1000 0000 1100 0100 1010 0010 1110 0110 1001 0001 1101 0101
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...