8101 Datasheet, PDF (39/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

Undersize packets are packets whose length is less than the minimum
packet size. Minimum packet size is defined to be 64 bytes, exclusive of
preamble and SFD. If a received packet is an undersize packet, the
frame is determined to be invalid and is discarded. Refer to Section 2.13,
“Packet Discard” for more information about discards. Clearing the
DIS_USIZE bit in “Register 8–Configuration 2‚" Section 4.3.9, programs
the controller not to discard an undersize packet.
2.8.8 Maximum Packet Size
The maximum packet size used for receive MAC frame validity checking
is programmed to be one of four values, 1518, 1522, 1535 or unlimited
bytes. Setting the RMXPKT[1:0] receive MAC maximum packet size
select bits in “Register 9–Configuration 3‚" Section 4.3.10, and the
DIS_OSIZE bit in “Register 8–Configuration 2‚" Section 4.3.9, as shown
in Table 2.6. programs the controller to discard packets that exceed the
maximum packet size selected. This selection is also described in the
register descriptions for those registers.
The bits shown in Table 2.6 affect the receive MAC section only; the
maximum packet size for the management counters is described in
Section 2.19, “Counters”.
Table 2.6 Receive Maximum Packet Size Selection
Register 8
DIS_OSIZE Bit
0b0
0b1
0b1
0b1
1. xx = Don’t Care
Register 9
Maximum
RMXPKT [1:0] Bits Packet Size (Bytes)
xx¹
unlimited
0b10
1535
0b01
1522
0b00
1518
2.8.9 MAC Control Frame Check
The length/type field is checked to detect whether the packet is a valid
MAC control frame. Refer to Section 2.17, “MAC Control Frames” for
more details on MAC control frames.
Receive MAC
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