Intel 80287, 80286 manual System Initialization

80286 SYSTEM INITIALIZATION

Form an adlij!lmenl faclor from Ihe r~al CS bale of FFOOOOH 10 Ihe !egmenl bale address assumed by ASM286 •. Any data reference made

Inlo CS mij!1 add an Indexing lerm IBPI 10 compen!ale for Ihe difference belween Ihe off!el genera led by ASM286 and Ihe off!el reqijlred from Ihe bale of FFOOOOH.

Ia r I	proc			The valije of IP al rijn lime will nol be
				Ihe lame a! Ihe one ij!ed by ASM286!
!larI1:	c a II	!larl1		Get Irije off!el of !lart1
	pop	bp
	!ijb	bp,offul !larl1		Sijblracl ASM286 offset of !lart1
				leaving adlij!lment faclor In BP
	II d t	I n I I I a I_g d I I bpi		Setijp nijll IDT 10 force shij1down
				on any protecllon error or Inlerrijpt
	Copy the EPROM-ba!ed lemporary GDT Inlo RAM.
	lea	!I,lnlllal_gdllbpl	;	Selijp polnler 10 lemporary GDT
				templale In EPROM
	mov	c x , ( e n d_g d I - I n III a I_g d I ) I 2		5 e I len g I h
rep	maY!	es:word plr Idll,cs:lslli Pijl Inlo reserved RAM area

Look for 80287 processor exten!lon. A!sijme all one! will. be read If an 80287 15 nol pre!enl.

f n I n I I		Inillalize			80287	If preunt
mov	bx,EM	A!!ume		no	80287
htsw	ax	Look	al	!lah! of		80287
or	a I, a I	Ho error.			!hould	be pre!enl
In z	!el_mode	Jump	If	no	80287
hetpm		Put	80287		In t 0 protecled mode
mov	bx,MP

Swllch to prolecled mode and !elup a stack, GDT, and LDT.

i
!el_mode:		Get	current MSW
!m!w	ax
or	.. ,PE	Sel	PE	bit
or	ax,bx	Sel	HPX !lalu!		flag!
Im!w	ax	Enter		prolected	mode!
Imp	i .2	Clear qijeij~ of In,lr"ctlon~ decoded
		while In Real Addre!s Mode
		CPL 15 now 0, CS !IIII polnl! at
		FFFE10		In phy!lcal memory

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