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Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual 75
Host Software Interface
Default - 0 (off).
Recommended - 0.
VLAN TCO: On the 82559, this bit activates VLAN capability filtering of received TCO
packets at nominal D0 state. When this bit is clear, the 82559 implements receive TCO in
D0 for non-tagged TCO packets only. If this bit is set, the 82559 looks for both tagged and
non-tagged TCO packets. When the 82559 is in the power down state or the Force TCO
state, the 82559 looks for the VLAN type for recognition of tagged versus non-tagged
packets. In all other states, the 82559 does not look for the VLAN type for qualification.
0 = Only TCO packets without VLAN headers are supported.
1 = TCO packets with or without VLAN headers are supported.
Default - 0 (off).
Recommended - 0.
— Bit 0 - TCP/UDP Checksum. This bit is reserved on the 82557 and 82558, and should be
set to 0 on those devices. This bit was added for the 82559. When this bit is set to ‘1, the
82559 provides a checksum word of incoming packets, excluding MAC header and CRC.
A detailed description of the checksum calculation and memory structure can be found in
Section 6.4.3.4, “No Buffer Performance Improvements (82558 and 82559)”.
0 = Disabled.
1 = Enabled.
Default - 0.
Recommended - 0 (unless the NOS supports TCP/UDP checksum offload).
• BYTE 10.
— Bits 7:6 - Loopback. This bit defines the type of loopback.
00 = Normal operation (no loopback).
01 - Internal loopback.
10 - Reserved.
11 - External loopback (loopback pin active).
Default - 00.
Recommended - 00.
— Bits 5:4 - Pre-amble Length. This bit selects the length of the pre-amble, not including the
SFD, according to table below.
Default setting - 10b (7 bytes).
Recommended - 10b.
— Bit 3 - No Source Address Insertion. This bit determines the source of the source address.
0 = SA insertion (SA comes from internal device IA).
1 = No SA insertion (SA comes from memory).
Table 46. Pre-amble Length
D5 D4 Preamble Length
0 0 1 byte
0 1 3 bytes
1 0 7 bytes
1 1 15 bytes