0.00-050613_boot.s

 !    boot.s
 !
 ! It then loads the system at 0x10000, using BIOS interrupts. Thereafter
 ! it disables all interrupts, changes to protected mode, and calls the 

 BOOTSEG = 0x07c0
 SYSSEG  = 0x1000            ! system loaded at 0x10000 ().
 SYSLEN  =                 ! sectors occupied.

 entry start
 start:
     jmpi    go,#BOOTSEG
 go:    mov    ax,cs
     mov    ds,ax
     mov    ss,ax
     mov    sp,#0x400        ! arbitrary value >>

 ! ok, we've written the message, now
 load_system:
     mov    dx,#0x0000
     mov    cx,#0x0002
     mov    ax,#SYSSEG
     mov    es,ax
     xor    bx,bx
     mov    ax,#0x200+SYSLEN
     int     0x13
     jnc    ok_load
 die:    jmp    die

 ! now we want to move to protected mode ...
 ok_load:
     cli            ! no interrupts allowed !
     mov    ax, #SYSSEG
     mov    ds, ax
     xor    ax, ax
     mov    es, ax
     mov    cx, #0x2000
     sub    si,si
     sub    di,di
     rep
     movw
     mov    ax, #BOOTSEG
     mov    ds, ax
     lidt    idt_48        ! load idt with 0,0
     lgdt    gdt_48        ! load gdt with whatever appropriate

 ! absolute address 0x00000, in 32-bit protected mode.
     mov    ax,#0x0001    ! protected mode (PE) bit
     lmsw    ax        ! This is it!
     jmpi    0,8        ! jmp offset 0 of segment 8 (cs)

 gdt:    .word    0,0,0,0        ! dummy

     .word    0x07FF        ! 8Mb - limit=2047 (2048*4096=8Mb)
     .word    0x0000        ! base address=0x00000
     .word    0x9A00        ! code read/exec
     .word    0x00C0        ! granularity=4096, 386

     .word    0x07FF        ! 8Mb - limit=2047 (2048*4096=8Mb)
     .word    0x0000        ! base address=0x00000
     .word    0x9200        ! data read/write
     .word    0x00C0        ! granularity=4096, 386

 idt_48: .word    0        ! idt limit=0
     .word    0,0        ! idt base=0L
 gdt_48: .word    0x7ff        ! gdt limit=2048, 256 GDT entries
     .word    0x7c00+gdt,0    ! gdt base = 07xxx
 .org 510
     .word   0xAA55

C