Intel 80286, 80287 manual Ax,.x

inter

I 9 d I mov mov xor II d I

mov I I r

80286 SYSTEM INITIALIZATION

I em p_. I a c k [ bpi	U.e	I n I I I a I	GDT	I n	RAM arel
ax, lemp_. tac k -I n I I lal_gdl	; Selup SS		wI I h	vall d		prolected mode
!!IS,IIX	.eleclor 10 Ihe RAM					GDT	and	• I a ok
a x I a x	Sel Ihe current LDT 10 null
ax	Any	references		10	I I	will	CIlU!!Ie
	an excepllon cau.lng .huld.wn
a x, • a v e_ I •• - I n I I I a I_g d I	Set	I n I I I a I	TSS	I n I 0		I he	10.	RAM
a x	The	I a • k .wllch		need.		a vall d		TSS

Copy Ihe EPROM-ba.ed GDT Inlo Ihe RAM data .egmenl 0110 •.

Flr.1 the descrlplor for the RAM data segmenl must be copied Into the temporary GDT.

mov cmp

Jb

mov mov call mov mov

c a I 1

mov mov mov

I 9 d t

a x , 9 d t_d e!C [ bpI. II mI I ax,S'slze desc-!

bad_gdl

b x, 9 d t_d e. c - I nit lal_g d I

.I,gdt_allas copy_EPROM_dt s I , I d I_a II a s

b x, I d I_d esc - I n I I I a I_g d I copy_EPROM_dl

a x , 9d t _d esc - I nit I a I_g d I

d s , a x

bx,gdt_allas

[b x I

Gel size of GDT

Be .ure Ihe lasl enlry expecled by this code Is Inside Ihe GDT

Jump If GDT I. not big enough

Form selector 10 EPROM GDT Get selector of GDT alias Copy Into EPROM

Get selector of lDT alias [ndlcate EPROM [DT

Setup addre.slng Inlo EPROM GDT

Gel GDT alia. data segmenl .elector Sel GDT to RAM GDT

SS and TR remain In low RAM

Copy all task's TSS and LDT . • egmenls Inlo RAM

I e a

copy_task_loop: call add mov

or

Jnz

With

	Define		list of		tasks 10 setup
copy_la.ks	Copy	them		Inlo	RAM
b x , s I z e I ask _e n try	Go to		next	entry
ax,cl: [bxl. tss_sel	See If		Ihere Is		another enlry

ax,.x

copy_la.k_loop

TSS, GDT, and LDT set, .tarlup the Initial task!

mov	b x, 9 d t_a Ila.
mov	d. , b x
mov	b x , I d .I_a I I a •
II d t	[b x I
Jmp	.tart_polnter[bpl

Potnt DS at GDT

Get lDT alias data .egment .elector Set [DT for errors and Interrupt. Slarl Ihe flrsl lask!

The low RAM area Is overwrllten with Ihe current CPU conlexl

Halt here If GDT Is not big enough

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