assembly - Trying to return from Protected Mode to Real -

i'm trying go real mode, after protected, , processor got stuck right after changing cr0 register. i'm using nasm, , compile program binary .img run under virtualbox bootloader. i'm missing long jump realmain proc.

[org 0x7c00] ; bios boot origin [bits 16] ; 16-bit real mode  jmp start ;jump start() entry-point %include "routines16.asm" [bits 16]  start:   mov si, welcomemsg   call print   call getkey   call clear  realmain:   cli   mov ax, cs   mov ds, ax   mov es, ax   ; mov ax, stack16   ; mov ss, ax   sti    mov si, inrealmsg   call print    mov si, anykeymsg   call print   call getkey    call toprotected  toprotected:   mov si, toprotectedmsg   call print   call clear;   ;move   cli   lgdt [gdt32_descriptor] ; load gdt   mov eax, cr0   or eax, 0x1   mov cr0, eax   jmp dword code_seg_32:protectedmain  ;;;;;;;;;;;;;; welcomemsg db "ipr1-degtyarev. press key start", 0x0 inrealmsg db "in real", 0x0 toprotectedmsg db "switching protected", 0x0 anykeymsg db "press key switch cpu mode...", 0x0 ;;;;;;;;;;;;;;  %include "gdt32.asm" %include "routines32.asm"  [bits 32]  protectedmain:   mov eax, data_seg_32   mov ds, eax   mov es, eax    mov eax, 0x0000; 0 line   mov ebx, inprotectedmsg   call print32   add eax, 0x00a0; moving next line   call toreal  toreal:   mov edx, eax   mov ebx, torealmsg   call print32   ;move   cli    mov eax, cr0   dec al   mov cr0, eax    jmp 0x7c00:realmain  end:   jmp end  ;;;;;;;;;;;;;; inprotectedmsg db "in protected", 0x0 torealmsg db "switching real", 0x0 ;;;;;;;;;;;;;;  times 510 - ($-$$) db 0 ;fill rest of bootloader zeros dw 0xaa55 ;boot signature 

attached gdt32

; descriptor config gdt32_start:  gdt32_null:         ; initialization null     dq 0x0  gdt32_cs:     dw 0xffff    ; limit     dw 0x0000    ; base     db 0x0000    ; base 23:16     db 10011011b ; [p][dpl][][s][type][][][a]     db 11011111b ; [g][x][0][avl][lim][][][]     db 0x0000  gdt32_ds:     dw 0xffff    ; limit     dw 0x0000    ; base     db 0x0000    ; base 23:16     db 10010011b     db 11011111b     db 0x0000  gdt32_end:         ; pour avoir la taille du gdt  gdt32_descriptor:     dw gdt32_end - gdt32_start - 1 ; gdt size     dd gdt32_start  ; constants address of gdt32 code_seg_32 equ gdt32_cs - gdt32_start data_seg_32 equ gdt32_ds - gdt32_start