I am creating an operating system since this summer, it is an 32 bits operating system which work in protected mode. I need to creat a way to make BIOS interrupt so I need to pass in real mode and before in 16bit, I sucessfully pass to 16 bit but I am not sure that I pass in real mode at the end of my code. I try by example to switch video mode but my emulator, Boch write :
00012417016e[CPU0 ] interrupt(real mode) vector > idtr.limit
00012417016e[CPU0 ] interrupt(real mode) vector > idtr.limit
00012417016e[CPU0 ] interrupt(real mode) vector > idtr.limit
00012417016i[CPU0 ] real mode
00012417016i[CPU0 ] CS.d_b = 16 bit
00012417016i[CPU0 ] SS.d_b = 16 bit
00012417016i[CPU0 ] | EAX=00004c00 EBX=00000123 ECX=00000000 EDX=00001034
00012417016i[CPU0 ] | ESP=0009f000 EBP=0009effc ESI=00000123 EDI=0000ffde
00012417016i[CPU0 ] | IOPL=0 id vip codec vm RF nt of df IF tf sf zf af pf cf
00012417016i[CPU0 ] | SEG selector base limit G D
00012417016i[CPU0 ] | SEG sltr(index|ti|rpl) base limit G D
00012417016i[CPU0 ] | CS:0000( 0004| 0| 0) 00000000 0000ffff 0 0
00012417016i[CPU0 ] | DS:07c0( 0005| 0| 0) 00007c00 0000ffff 0 0
00012417016i[CPU0 ] | SS:8000( 0005| 0| 0) 00080000 0000ffff 0 0
00012417016i[CPU0 ] | ES:07c0( 0005| 0| 0) 00007c00 0000ffff 0 0
00012417016i[CPU0 ] | FS:0000( 0005| 0| 0) 00000000 0000ffff 0 0
00012417016i[CPU0 ] | GS:0000( 0005| 0| 0) 00000000 0000ffff 0 0
00012417016i[CPU0 ] | EIP=00001d63 (00001d63 )
00012417016i[CPU0 ] | CR0=0x00000010 CR1=0 CR2=0x00000000
00012417016i[CPU0 ] | CR3=0x00000000 CR4=0x00000000
00012417016i[CPU0 ] >> int 0x21 : CD21
00012417016e[CPU0 ] exception(): 3rd (13) exception with no resolution, shutdown status is 00h, resetting
00012417016i[SYS ] bx_pc_system_c::Reset(SOFTWARE) called
My assembly codee to switch in real mode is :
global go16
;______________________________________________________________________________________________________
;Switch to 16-bit real Mode
;IN/OUT: nothing
go16:
[BITS 32]
;cli ;Clear interrupts
pop edx ;save return location in edx
jmp 0x20:PM16 ;Load CS with selector 0x20
;For go to 16-bit real mode, first we have to go to 16-bit protected mode
[BITS 16]
PM16:
mov ax, 0x28 ;0x28 is 16-bit protected mode selector.
mov ss, ax
mov ds, ax
mov es, ax
mov gs, ax
mov fs, ax
mov sp, 0x7c00+0x200 ;Stack hase base at 0x7c00+0x200
mov eax, cr0
mov [savcr0], eax
and eax, 0xfffffffe ;Clear protected enable bit in cr0
mov cr0, eax
jmp 0:realMode ;Load CS and IP
realMode:
;Load segment registers with 16-bit Values.
mov ax, 0
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov sp, 0x7c00+0x200
mov ax, 0x07c0
mov ds, ax
mov es, ax
mov ax, 0x8000
mov ss, ax
mov sp, 0xf000
lidt [idt_real] ;Load real mode interrupt vector table
sti
mov ax,4c00h
int 10h
cli
hlt
;Real mode interrupt vector table
idt_real:
dw 0x3ff ; 256 entries, 4b each = 1K
dd 0 ; Real Mode IVT @ 0x0000
savcr0:
dd 0
Thank you for your help, if you need some other elements ask them to me in comments the
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