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We can now switch to 32-bit mode.

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This commit is contained in:
David Given 2022-08-08 23:22:00 +02:00
parent 1e0961c679
commit 21b30ccadb
1 changed files with 38 additions and 29 deletions
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67
plat/msdos386/boot.s
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@ -45,9 +45,8 @@ dpmi_cs = 0x2c
dpmi_sp = 0x2e
dpmi_ss = 0x30
dpmi_ps = 0x32 ! WORD: protected register segment
dpmi_rs = 0x34 ! WORD: real register segment
dpmi_psp = 0x36 ! WORD: PSP segment
dpmi_rs = 0x32 ! WORD: real segment
dpmi_psp = 0x34 ! WORD: PSP segment
dpmi_switch = 0x38 ! DWORD: far pointer of pmode switch routine
.seek 0x3c
@ -79,33 +78,10 @@ exe_start:
mov ax, 1 ! 32-bit app
callf (dpmi_switch)
jc no_pmode
jnc pmode ! Success!
mov (dpmi_edx), go_msg
mov ax, (dpmi_rs)
mov (dpmi_ds), ax
mov (dpmi_eax+1), 9
call int21
mov ax, 0x4c00
int 0x21
! Could not switch to protected mode.
! Simulate DOS interrupt bx.
int21:
mov bx, 0x21
callint:
xor ax, ax
mov (dpmi_ss), ax ! zero stack: DPMI host allocates one.
mov (dpmi_sp), ax
push ds
pop es
mov di, ax
mov ax, 0x300
int 0x31 ! simulate DOS interrupt
push cs
pop ds
ret
no_pmode: ! Could not switch to protected mode.
mov dx, no_pmode_msg
jmp exit_with_error
@ -120,8 +96,41 @@ exit_with_error:
mov ax, 0x4cff
int 0x21 ! terminate with error code al
pmode:
! We're now in protected mode! Switch our code segment to 32-bit mode.
mov cx, cs
lar cx, cx
movb cl, ch
movb ch, 0xc0
mov bx, cs
mov ax, 0x0009
int 0x31 ! Make selector 32 bit
.use32
start_32bit:
o16 mov (dpmi_edx), go_msg
o16 mov ax, (dpmi_rs)
o16 mov (dpmi_ds), ax
movb (dpmi_eax+1), 9
call int21
o16 mov ax, 0x4c00
int 0x21
! Simulate DOS interrupt bx.
int21:
o16 mov bx, 0x21
callint:
o16 xor ax, ax
o16 mov (dpmi_ss), ax ! zero stack: DPMI host allocates one.
o16 mov (dpmi_sp), ax
push ds
pop es
mov di, ax
o16 mov ax, 0x300
int 0x31 ! simulate DOS interrupt
push cs
pop ds
ret
go_msg:
.ascii "Go!$"