Intel PCI-X manual Ctrl Register Bit Description, Field Bits Initial Description Value

			Register Descriptions
Table 13-3. CTRL Register Bit Description
31			0
			Device Control Bits
Field	Bit(s)	Initial	Description
		Value
			Full-Duplex
			Enables software to override the hardware Auto-Negotiation
			function. The FD sets the duplex mode only if CTRL.FRCDPLX
			is set.
			When cleared, the Ethernet controller operates in half-duplex;
			when set, the Ethernet controller operates in full-duplex.
FD	0	1b	When the Ethernet controller operates in TBI mode/internal
		0b1	SerDes mode, and the AN Hardware is enabled, this bit is
			ignored. When the Ethernet controller operates in TBI mode/
			internal SerDes, and the AN Hardware is disabled, or the link is
			forced, this bit should be set by software.
			When the Ethernet controller operates in internal PHY mode,
			the FD bit is set by software based on AN and data rate
			resolution.
			Configurable through the EEPROM.
Reserved	2:1	0b	These bits are reserved and should be set to 00b.
			Link Reset (not applicable to the 82540EP/EM, 82541xx, or
			82547GI/EI)
			0b = Normal; 1b = Link Reset
			Applicable only in TBI mode/internal SerDes of operation. Used
LRST	3	1b	to reset the link control logic and restart the Auto-Negotiation
			process, when TXCW.ANE is set and TBI mode/internal SerDes
			is enabled.
			When set, transmission and reception are halted regardless of
			TBI mode/internal SerDes setting. A transition to 0b initiates the
			Auto-Negotiation function. Configurable from the EEPROM,
			allowing initiation of Auto-Negotiation function at power up.
Reserved	4	0b	Reserved
			Factory use only. Should be written with 0b.
			Auto-Speed Detection Enable.
			When set, the Ethernet controller automatically detects the
			resolved speed of the link by sampling the link in internal PHY
ASDE	5	0b	mode and self-configures the appropriate status and control
			bits. Software must also set the SLU bit for this operation. This
			function is ignored in TBI mode/internal Serdes. The ASD
			feature provides a method of determining the link speed without
			the need for software accesses to the MII management
			registers.

Software Developer’s Manual 221