Bitfields for Intel 82371SB legacy support register:
Bit(s)	Description	)
 15	A20GATE pass-through sequence ended
	write 1 to clear this bit
 14	reserved
 13	USB PIRQ enabled
 12	USR IRQ status (read-only)
 11	trap caused by write to PORT 0064h
	write 1 to clear this bit
 10	trap caused by read from PORT 0064h
	write 1 to clear this bit
 9	trap caused by write to PORT 0060h
	write 1 to clear this bit
 8	trap caused by read from PORT 0060h
	write 1 to clear this bit
 7	enable SMI at end of A20GATE Pass-Through
 6	A20GATE pass-through sequence in progress (read-only)
 5	enable A20GATE pass-through sequence
	(write PORT 64h,D1h; write 60h,xxh; read 64h; write 64h,FFh)
 4	enable trap/SMI on USB IRQ
 3	enable trap/SMI on PORT 0064h write
 2	enable trap/SMI on PORT 0064h read
 1	enable trap/SMI on PORT 0060h write
 0	enable trap/SMI on PORT 0060h read
SeeAlso: #01215,#01225