
Chapter 3
Functional Operation
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AMD-8111 HyperTransport I/O Hub Data Sheet
AMD Preliminary Information
The Logical Address Filter block consists of a 64-bit Logical Address Filter Table and associated
control logic. The Logical Address Filter logic uses the CRC generator from the Frame Check
Sequence block to perform a calculation on the DA field of a frame to determine whether or not to
signal a match. The CRC generator calculates a CRC value for the DA field of the frame. If the
destination address is a multicast address, the 6 most significant bits of this CRC value are used as a
pointer to a bit in the Logical Address Filter Table. If the selected bit is 1, the Logical Address Filter
signals a match. See Figure 21 on page 96.
The broadcast address (all ones) is treated as a special case, not as an instance of a multicast address.
A frame addressed to the broadcast address does not cause a multicast address match. This means that
if the DRCVBC bit is set, broadcast frames are not received even if the bit in the Logical Address
Filter that corresponds to the broadcast address is set.
The host CPU can read and write the Logical Address Filter Register directly.
Although the Logical Address Filter rejects the vast majority of addresses that are not intended for
this device, it is not a perfect filter. More than one multicast address maps to each bit in the filter table.
Therefore the host software must compare the DA field of each frame that was accepted by the
Logical Address Filter with a software table of acceptable multicast addresses. If the Logical Address
Filter signals a match for an incoming frame, the Logical Address Filter Match (LAFM) bit is set in
the receive descriptor that corresponds to the frame. The host CPU can examine this bit to determine
whether or not it should look up the destination address in the software address table.
3.10.6.2.2 Address Match Classification
The receive descriptor associated with a frame includes 3 bits that indicate why the frame was
received.
The Physical Address Match (PAM) bit is set when the destination address matches the contents of
the PADR.
The Logical Address Filter Match (LAFM) bit is set when the destination address is a multicast
address that causes the Multicast Hash Filter to signal a match and the destination address is not the
broadcast address.
The Broadcast Address Match (BAM) bit is set when the destination address is the broadcast address.