Intel 80286, 80287 manual Mov!w

80286 SYSTEM INITIALIZATION

See If a valid LOT I. 'peclfled for the .tartup ta.k If . 0 I hen cop Y I h e EPRO M ve ...1 0 n I n lot heR AM a I I a •.

mov mov and

Jz

pu.h

I a r

J n z

mov and cmp

J n e

d • ,c. : [b x J . I •• _all a.

.I,d.:word plr LOT_OFFSET

.I,nol TJRPL_MASK n a_I d I

d I ,d h

dh,nol DPL

dh, DT_ACCESS bad_Idl

Addre •• TSS 10 get LOT

Ignore TI and RPL

Skip Ihl. If no LOT u.ed

Save LDT .eleclor Te.1 de.crlplor

Jump If Invalid .eleclor

Save LDT de.crlplor acce •• byle [gnore privilege

Be .ure II I. an LDT de.crlptor Jump If Invalid

mov mov

151

call mov

e.:[.IJ.acce.5,DS_ACCESS; Mark LDT a.		dala	.egmenl
d" .1	Polnl OS al	EPROM	LOT
IS X 1 5 1	Gel LDT Ilmil
Ie. I_d t_ll·m I I	Verify II i!.valld
ex 1 IS X	Save for later

Examine Ihe LDT alia •• egment and, If good, copy 10 RAM

mov mov

I • I

call

c a I I

Sel

• I , c. : I b x) . I d I_alia 5	Gel	Idl		all ••• eleelor
e!l , 51	Polnl		ES	al alia •• egmenl
IS X I !l1	Get	I~nglhof alla~ segment
le.l_dl_Ilmll	Verify II I. valid
cop y_w I I h_ f I I I	Copy		LDT	Inlo RAM alia •• egmenl
Ihe LDT Ilmil and ba.e	addre ••	10	Ihe RAM copy of Ihe LOT .

mov	• I ,c • : [ b x I . I d I _a I I ••
pop	d I
mov	ax.gdl_alla.
mov	d!i 1	I!I X
mov	e!l 1	1< X
mov!w

mov!iW

10 d • w

mov a h , d I

• Io.w

mov!lw

ret

bad_Idt:

hit

Re.lore LDT alia •• eleelor Re.lore LDT .eleclor

Re.lore GDT addre •• lng

Move Ihe RAM LDT Ilmil

Move Ihe low 16 bll. aero •• Gel Ihe high 8 bit.

Mark a. LDT de.erlptor

Sel high addre •• and aeee •• rlghl • Copy re.erved word

All done

Hall here If LDT I. Invalid

endp

A-7