Bitfields for AMD-640 Shadow RAM Control Register 3:
Bit(s)	Description	)
 7-6	segment E000h-EFFFh shadow RAM control
	00 shadowing disabled
	01 write enabled
	10 read enabled
	11 both read and write enabled
 5-4	segment F000h-FFFFh shadow RAM control
 3-2	ISA memory hole
	00 none
	01 = 512K-640K
	10 = 15M-16M
	11 = 14M-16M
 1	enable SMI redirection
	if set: 30000h-3FFFFh redirected to B0000h, 40000h-4FFFFh to A0000h
 0	redirect video RAM accesses (A0000h-BFFFFh) to system DRAM rather than
	  PCI bus (used to initialize SMRAM at B0000h)
SeeAlso: #00983,#00992,#00993