Frame Recognition
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
25-25
25.9.2 Destination Address Recognition
The Ethernet controller filters frame using the traditional destination address recognition
methods, with the following requirements:
Reject all must not be enabled (that is, RCTRL[RA] is cleared).
There should be no pattern matches with a decode of (PCNTRLn[PMC] = 10 or 11).
If a specific pattern has PCNTRLn[PMC] = 10 or 11, destination address filtering still occurs if
that specific pattern is not matched. With address recognition filtering, patterns are set up to
identify only frames that need special processing (filing to a specified queue). If a frame is
accepted due to destination address filtering and no pattern match occurs, the Ethernet controller
uses the default queue specified in DATTR as the destination queue.
The Ethernet controller identifies the type of the address. Hash table filtering, for example, can be
implemented with ease. The addresses are classified as physical (individual), group (multicast),
broadcast (all-ones group address), and promiscuous. The difference between an individual
address and a group address is determined by the I/G bit in the destination address field.
Additional fields in the frame can be searched for a pattern match. Figure 25-18 shows a
flowchart for address recognition on received frames. In the actual implementation, most
decision points shown in the figure occur simultaneously.
The Ethernet controller compares the destination address field of the received frame with the
physical address that you program in the station address registers (MACSTNADDR1 and
MACSTNADDR2). If the destination address does not match the station address, the controller
performs address recognition on multiple individual addresses using the IADDRn hash table.
You must write zeros to the hash to avoid a hash match and ones to the station address to avoid an
individual address match, or you can turn on Promiscuous mode (see page 25-78).
In the group type of address recognition, the Ethernet controller determines whether the group
address is a broadcast address. If it is a broadcast, and broadcast addresses are enabled, the frame
is conditionally accepted and further activity on the frame is determined by pattern matching. If
the group address is not a broadcast address, you can perform address recognition on multiple
group addresses using the GADDRn hash table. In Promiscuous mode, the Ethernet controller
receives all of the incoming frames, regardless of their address, but performs further processing
with pattern matching. Therefore, in Promiscuous mode the Ethernet controller allows all but a
few specific addresses to be received.
Address recognition allows the Ethernet controller to use the traditional destination address
selection criteria to determine which frames to keep and which to reject. Because pattern
matching takes place in the background even in address recognition mode, the controller can use
the pattern matching to implement features such as selectively storing some frames in one queue
and others in a different queue even if they had the same destination address. The pattern
matching capabilities are explained in detail in Section 25.10.2, Receive Frame Processing with
Pattern Matching, on page 25-30.
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