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76 Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
Host Software Interface
Default - 1.
Recommended - Depends on the NOS and driver environment.
• BYTE 11.
— Bits 2:0 - Linear Priority. These bits are reserved on the 82558 and 82559 and should be
set to 000b on those devices.
For the 82557, these bits correspond to he number of slot times that the device will wait
after the IFS or after backoff before enabling transmission. A higher number reduces the
priority. Stations with this value set to 0, the highest priority, conform to the IEEE 802.3
backoff algorithm.
Default - 000 (normal CSMA/CD operation).
Recommended - 000.
• BYTE 12.
— Bits 7:4 - Interframe Spacing. This field specifies the period (in multiples of 16 bit times)
that the device must defer after the later of the following two events:
• The last bit has been transmitted.
• Carrier sense becomes inactive.
Default - 96 (6 in the register).
Recommended - 6.
— Bit 0 - Linear Priority Mode. This bit is reserved on the 82558 and 82559 and should be
set to 1 for those devices. For the 82557, it determines the way the linear priority
mechanism works.
0 = Wait after transmit only. The device defers for IFS + N * slot time after the
transmission of the frame only.
1 = Wait transmit or receive. The device defers for IFS + N * slot time after the
transmission or reception of a frame.
N = Linear priority number.
Default - 0.
Recommended - 0.
• BYTE 13 and BYTE 14.
Bits 7:0 (byte 13 and byte14) - IP Address. This field is available only in the 82558 B-step.
Byte 13 should be set to 0h, and byte 14 should be set to F2h for the 82557, 82558 A-step, and
82559 devices.
For the 82558 B-step, this field holds the 16 least significant bits of the IP address used for
ARP frame filtering. For example, to configure the filter for ARP frames with an IP address of
012h 034h 056h 078h, the following values are written to the configuration block:
The ARP filter compares the value stored in offset 13 of the configuration block to the byte at
offset 41 in an ARP frame without a VLAN header and to byte 45 in ARP frames with a
VLAN header.
Table 47. 82558 B-step Configuration Block ARP Frame IP Address
Configuration Block
Offset
Configuration
Parameter Name
Example Value
13 IP Address Low 078h
14 IP Address High 056h