Intel Gigabit Ethernet Controllers ユーザーズマニュアル

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If one of the LAN devices is disabled, the Ethernet controller no longer is a multi-function device. 

It normally reports a 01h in the PCI Configuration Header field Header Type, indicating multi-

function capability. However, if a LAN id disabled, it reports a 0h in this filed to signify single-
function capability.

When both LAN devices are enabled, the Ethernet controller uses both the INTA# and INTB# pins 
for interrupt-reporting. The EEPROM Initialization Control Word 3 (bit 4) associated with each 

LAN device controls which of these two pins is used for each LAN device. The specific interrupt 

pin used is reported in the PCI Configuration Header Interrupt Pin field associated with each LAN 
device.

However, if either LAN device is disabled, then the INTA# be used for the remaining LAN device, 

regardless of the EEPROM configuration. Under these circumstances, the Interrupt Pin field of the 

PCI Header always reports a value of 1h, indicating INTA# usage.

When both LAN devices are enabled, the PCI Power Management Register Block has the 

capability of reporting a Common Power value. The Common Power value is reflected in the data 
field of the PCI Power Management registers. The value reported as Common Power is specified 

via EEPROM, and is reflected in the data field each time the Data_Select field has a value of 8h 

(8h = Common Power Value Select).

When either LAN is disabled and the Ethernet controller appears as a single-function device, the 
Common Power value, if selected, reports 0h (undefined value), as Common Power is undefined 

for a single-function device.