Broadcom BCM5722 - Table 43: Multicast Hash Table Registers

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Programmer’s Guide BCM5722

10/15/07

Broadcom Corporation

Document 5722-PG101-R Packet Filtering Page 98

CHECKING CRC

The following steps describe a method to check a stream of bytes, which has a CRC appended.

1. Set remainder to 0xFFFFFFFF.

2. For each bit of data starting with least-significant bit of each byte:

If right-most bit (bit-0) of the current remainder XORed with the data bit equal 1,

then remainder = (remainder shifted right one bit) XOR 0xEDB88320,

else remainder = (remainder shifted right one bit).

3. Remainder should equal magic value 0xDEBB20E3 if CRC is correct.

INITIALIZING THE MAC HASH REGISTERS

The 128-bit multicast hash table is treated as a single object occupying four BCM5722 Ethernet controller registers starting

at offset 0x0470 (see Table 43). The 128-bit value follows the big-endian ordering required by BCM5722 Ethernet controller.

Thus, the most significant 32-bit of the 128-bit value resides in Mac_Hash_Register_0 at offset 0x0470 and the least

significant 32-bit resides in Mac_Hash_Register_3 at offset 0x047c.

Host software can enable the reception of all multicast frames including broadcast frames by setting all four multicast hash

registers to 0xFFFFFFFF.

The C code fragment below will illustrate how to initialize the multicast hash table registers. The code fragment computes

the indices into hash table from a given list of multicast addresses and initializes the multicast hash registers.

Unsigned long HashReg[4];

Unsigned long j, McEntryCnt;

Unsigned char McTable[32][6];// List of multicast addresses to accept.

// Initialize the McTable here.

McEntryCnt = 32;

// Initialize the multicast table registers.

HashReg[0] = 0; // Mac_Hash_Regsiter_0 at offset 0x0470.

HashReg[1] = 0; // Mac_Hash_Register_1 at offset 0x0474.

HashReg[2] = 0; // Mac_Hash_Register_2 at offset 0x0478.

HashReg[3] = 0; // Mac_Hash_Register_3 at offset 0x047c.

for(j = 0; j < McEntryCnt; j++)

{

unsigned long RegIndex;

unsigned long Bitpos;

unsigned long Crc32;

Crc32 = ComputeCrc32(McTable[j], 6);

Table 43: Multicast Hash Table Registers

Mac_Hash_Register_0 0x0470 Most significant 32-bit of the 128-bit hash table

Mac_Hash_Register_1 0x0474 Bits 64:93 of the 128-bit hash table

Mac_Hash_Register_2 0x0478 Bits 32:63 of the 128-bit hash table

Mac_Hash_Register_3 0x047c Least significant 32-bit of the 128-bit hash table