
94
Functional Operation
Chapter 3
AMD-8111 HyperTransport I/O Hub Data Sheet
24674
Rev. 3.00
April 2003
AMD Preliminary Information
For test purposes, the controller can be programmed to accept runt packets of 12 bytes or larger by
setting RPA in CMD2.
3.10.6.2
Address Matching
MAC addresses are classified as either unicast, multicast, or broadcast. The least significant bit of the
first octet of a MAC address (the I/G bit) indicates whether the address is unicast (individual) or
multicast (group). If the bit is 0, the address is an individual address and is intended to be received by
a single network station. If the bit is 1, the address is a group address and is intended to be received by
more than one network station. The special address that consists of all 1s is known as the broadcast
address. Frames addressed to the broadcast address are intended to be received by all stations on the
local area network.
The network controller contains three address matching mechanisms that determine which incoming
frames it will receive:
1. The Physical Address Match Comparator
2. The Broadcast Address Match Comparator
3. The Multicast Hash Filter
In addition if the Promiscuous Mode bit (PROM, CMD2, bit 16) is set, all valid frames are received.
An incoming frame is saved in system memory if any one of these mechanisms signals a match for
that frame.
The Physical Address Match Comparator signals a match if the Destination Address (DA) field of the
incoming frame exactly matches the contents of the Physical Address Register (PADR). The byte
ordering is such that the first byte received from the network (after the SFD) must match the least
significant byte of PADR (PADR[7:0]), and the sixth byte received must match the most significant
byte of PADR (PADR[47:40]). The Physical Address Match comparator can be disabled by setting
the Disable Receive Physical Address Match (DRCVPA) bit in the CMD2 register.
The Broadcast Address Match Comparator signals a match if the Destination Address (DA) field of
the incoming frame is all ones. The Broadcast Address Match comparator can be disabled by setting
the Disable Receive Broadcast Address Match (DRCVBC) bit in the CMD2 register. If DRCVBC is
set and PROM is cleared, no broadcast frames are received even if another address match function
signals a match.
3.10.6.2.1 The Logical Address Filter
If the least significant bit of the first octet of a MAC address (as transmitted over the network) is a 1,
the address is a multicast (or logical) address that indicates that the frame is meant to be received by
more than one network node. The network controller can be programmed to accept frames addressed
to any number of multicast addresses. The Logical Address Filter is used to filter out unwanted
multicast frames.