User's Manual

80286 SYSTEM INITIALIZATION
See If a valid LOT I. 'peclfled for the .tartup ta.k
If. 0 I hen cop Y I h e E PRO M ve .. .1 0 n I n lot heR A M 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 e.:[.IJ.acce.5,DS_ACCESS; Mark LDT a. dala .egmenl
mov d".1 Polnl OS al EPROM LOT
151
call
mov
IS X 1 5 1
Ie. I_d t_ll·m I I
ex 1 IS X
Gel LDT Ilmil
Verify II i!.valld
Save for later
Examine Ihe LDT alia •• egment and, If good, copy 10 RAM
mov
mov
I • I
call
c a I I
• I , c. : I b x) . I d I_alia 5
e!l , 51
IS X I !l1
le.l_dl_Ilmll
cop y_w I I h_ f I I I
Gel Idl all ••• eleelor
Polnl ES al alia •• egmenl
Get I~nglhof alla~ segment
Verify II I. valid
Copy LDT Inlo RAM alia •• egmenl
Sel Ihe LDT Ilmil and ba.e addre •• 10 Ihe RAM copy of Ihe LOT .
mov
pop
mov
mov
mov
mov!w
mov!iW
10 d • w
mov
• Io.w
mov!lw
ret
bad_Idt:
hit
• I ,c • : [ b x I . I d I _a I I ••
d I
ax.gdl_alla.
d!i 1 I!I X
e!l 1 1< X
a h , d I
endp
A-7
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