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PATIO_COM:
;PATIO.COM
;
;         This program will load our 32-bit kernel
;         into physical address 1048576.
;
;         version 2017-06-17
;;

bits 16
org 100h



;Print program identification:
;;
 mov ah,9
 mov dx,str_kernelloader
 int 21h




;Open file read only:
;;
 mov ax,3D00h
 mov dx,kernel_bin
 int 21h
 jnc .noerr

  ;If we are here, print error:
  ;;
   mov ah,9
   mov dx,str_fileopenerr
   int 21h

 .noerr:
 mov [file_handle],ax

mov ah,9
mov dx,str_openkernfile
int 21h




.readkernloop:

mov ah,9
mov dx,str_readingkernfromdos
int 21h


 mov ah,3Fh            ;Service -.- read from file
 mov bx,[file_handle]  ;File handle by AH==3Dh
 mov dx,data_cache     ;Our temporary file read buffer
; mov cx,65535          ;Number of bytes to read
 mov cx,512            ;Number of bytes to read
 int 21h               ;Execute
 jc .kernreaderr       ;If CF==1, there was a read error


  ;;;INIT: Copy the kernel to its final destination
  ;;;INIT: Copy the kernel to its final destination
  ;;;INIT: Copy the kernel to its final destination
  ;;;INIT: Copy the kernel to its final destination

   cli
   push ds
   push es
   push cx
   push ax
    mov esi,data_cache
    xor ebp,ebp
    mov bp,ds
    shl ebp,4
    add esi,ebp

    mov edi,[final_kern_buff_ptr]

    mov ecx,512
    ;mov ecx,65535

    xor eax,eax
    mov ds,ax
    mov es,ax

    a32 o32 rep movsb
   pop ax
   pop cx
   pop es
   pop ds
    ;mov [final_kern_buff_ptr],edi
    add dword[final_kern_buff_ptr],512
   sti


  ;;;END:  Copy the kernel to its final destination
  ;;;END:  Copy the kernel to its final destination
  ;;;END:  Copy the kernel to its final destination
  ;;;END:  Copy the kernel to its final destination




 ;See if we already read all of the file.
 ;If AX and CX are different, then it means
 ;that we alreade read it all:
 ;;
  cmp ax,cx
  jne .kernreadend

jmp .readkernloop



.kernreaderr:
;If we are here, there was a kernel read error:
;;
 mov ah,9
 mov dx,str_fileopenerrread
 int 21h
 jmp .END


.kernreadend:
;;;INIT: Enable Protected Mode with local program GDT and jump to it
;;;INIT: Enable Protected Mode with local program GDT and jump to it
;;;INIT: Enable Protected Mode with local program GDT and jump to it
;;;INIT: Enable Protected Mode with local program GDT and jump to it

;Print that we are finally jumping into the kernel:
;;
 mov ah,9
 mov dx,str_kernjump
 int 21h

       ;Adjust the actual pointer of the GDT
       ;to where DOS has actually loaded this program:
       ;;
        mov eax,[GDT_actualptr]
        xor ebp,ebp
        mov bp,ds
        shl ebp,4
        add eax,ebp
        mov [GDT_actualptr],eax



        lgdt    [ds:GDT]              ;Load GDT. This is how we would
                                      ;exactly access the GDT in
                                      ;real mode

        cli     ;v2012-05-31
	mov	eax, CR0		;Turn on protected mode
	or	eax, 0x00000001         ;v2012-05-31
	mov	CR0, eax
        mov     ax, SELDat32            ;Setup ds and es
	mov	ds, ax
	mov	es, ax

       ;Indicate in EAX that we have loaded
       ;our kernel from a flavor of DOS, and thus
       ;we can exit our kernel back to it.
       ;We just need to learn to be increasingly
       ;careful to leave all of the hardware
       ;and CPU environment as it was before we
       ;loaded our OS, or as compatible as possible
       ;to avoid DOS from freezing.
       ;;
        mov eax,"DOSL"
        mov edx,"OAD1"


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;        jmp dword SELCod32:0xFF800000   ;Go
;     a32   jmp dword SELCod32:0x100000   ;Go
     a32   call dword SELCod32:0x100000   ;Go


 ;We will return to this point if we use
 ;the "exittodos" command of our
 ;LowEST Kernel console.
 ;
 ;We will need to learn a lot from DPMI
 ;to know how to properly disable paging
 ;and any other thing, as well as to use
 ;newly-developed multitasking structures
 ;whose first genuine task will be to save
 ;the machine state right after entering
 ;the kernel, for being able to return
 ;to our previous OS, more commonly DOS,
 ;or being able to return to the BIOS boot-level
 ;to execute INT 19h and load any other OS
 ;without rebooting the machine, which are things
 ;that will help us better understand the fine
 ;details of the machine and manage them
 ;by knowing that they are there, which will
 ;yield tiny hacking-grade tricks for low-level
 ;programming:
 ;;
  cli

 ;Disable Protected Mode:
 ;;
  mov eax,cr0
  dec eax
  mov cr0,eax


;;;END:  Enable Protected Mode with local program GDT and jump to it
;;;END:  Enable Protected Mode with local program GDT and jump to it
;;;END:  Enable Protected Mode with local program GDT and jump to it
;;;END:  Enable Protected Mode with local program GDT and jump to it






.END:
;Return to DOS:
;;
 sti
 mov ax,4C00h
 int 21h







kernel_bin db "kernel.bin",0
file_handle dw 0

final_kern_buff_ptr dd 1048576



str_kernelloader db "32-Bit LowEST Kernel Loader for DOS",10,13,"$"

str_openkernfile db "Opening KERNEL.BIN file for reading...",10,13,"$"

str_fileopenerr db "Error opening file KERNEL.BIN",10,13,0

str_readingkernfromdos db "Reading kernel file from DOS...",10,13,"$"

str_fileopenerrread db "Read error while reading KERNEL.BIN",10,13,0

str_kernjump db "Jumping into 32-bit kernel at 0x100000...",10,13,"$"









 ;INIT: GDT
 ;INIT: GDT
 ;INIT: GDT
    GDT:
   _SELNull equ 0   ;WARNING: This selector, besides being the pointer to the GDT
        GDT_size:   ;         is the null selector.
        dw GDTsize
        GDT_actualptr:
        dd GDT
       dw 0x0000

   _SELCod32 equ 8
     dw 0FFFFh       ; bits 0-15 length
     dw 00000h       ; bits 0-15 base address
     db 0            ; bits 16-23 base address
     db 10011010b    ; bits P,DPL,DT and type
     db 11001111b    ; bits G,D and bits 16-19 length
     db 0            ; bits 24-31 base address

   _SELDat32 equ 16  ;this is the "plain data selector"
     dw 0FFFFh       ; bits 0-15 length
     dw 00000h       ; bits 0-15 base address
     db 0            ; bits 16-23 base address
     db 10010010b    ; bits P,DPL,DT and type
     db 11001111b    ; bits G,D and bits 16-19 length
     db 0            ; bits 24-31 base address
   GDT_end:

   GDTsize equ (GDT_end-GDT)-1


  SELNull  equ 0
  SELCod32 equ 8
  SELDat32 equ 16
 ;END:  GDT
 ;END:  GDT
 ;END:  GDT







data_cache times 512 db 0


;EOF