Bitfields for Intel 82437,82439HX/TX,82443BX/EX/LX SMRAM control register:
Bit(s)	Description	)
 7	reserved
 6	SMM Space Open
	=1 make SMM DRAM visible even when not in SMM if bit 4 =0
 5	SMM Space Closed
	=1 no data references permitted to SMM DRAM even in SMM
 4	SMM Space Locked
	=1 force bits 4 and 6 to become read-only; and clear bit 6
 3	SMRAM Enable
	=1 128K DRAM are accessible for use at A000 while in SMM
 2-0	SMM Space Base Segment
	010 segment A000-BFFF
	100 segment C000-CFFF (82437MX,82443EX only)
	other reserved
Note:	bits 5 and 6 must never both be set at the same time
SeeAlso: #01099,#01108,#01098,#01124,#01106,#01107,#01142,#01129