.code16gcc
.global _start
.text
.align 4
_start:

###### A20 ########

     pushl  %eax
     pushl  %ecx            # needed to save, (demo code is like this)

     cli
     

     xor  %eax,  %eax 

     movw $0x2401 ,  %ax
     int  $0x15             #al 00-disabled 01-enabled

     movw $0x2402 ,  %ax
     int  $0x15             #al 00-disabled 01-enabled


     sti

     popl   %ecx
     popl   %eax


###################

##### VESA #######

     pushw %di
     pushl %eax
     pushl %ecx
     pushw %bx

     movw  $0x8000, %di

     movw  $0x4115, %bx
     movw $0x4f02, %ax

     int  $0x10

     movb  %ah,  number

     popw %bx
     popl %ecx
     popl %eax
     popw %di
 
#########################

########  protected mode ########
     cli
 
     lgdt   gdt_48
     movl   %cr0,  %eax
     orl    $1 , %eax
     movl   %eax, %cr0

     ljmp     $0x8, $protcseg
#################################

####### write video ram ####
.code32
write_vram:

     sti

     pushl  %eax
     pushw  %ds
     pushw  %di


#.byte 0x66  
     movl $0xe0000000, %eax
     addl $720000,      %eax
     movw   %fs,  %cx
     movw   %cx,  %di

     calll  main2          
     jmp .                 # remove these two lines to show assembly drawing


     movl $800, %ecx
loop:

     movl $0x00ff0000, (%eax)

     addl $3,   %eax
     subl $1,   %ecx
     cmp  $0,   %ecx
     jnz  loop
 
     popw  %di
     popw  %ds
     popl  %eax

     jmp .

##################


.code16gcc
##### base code ###
base:
   pushw %ds
   pushw %es
   pushw %ss

   movw %cs, %ax
   movw %ax, %ds
   movw %ax, %es
   movw %ax, %ss

    pushw %sp   

    movw $stack, %ax
    movw  %ax, %sp

    calll  main2

    popw %sp
    movw $stack, %sp

    popw %ss
    popw %es
    popw %ds


    hlt 


message:
   .string "Hello, world!\n\0"

.global display_str
display_str:
  pushl        %ebp
  movl   %esp, %ebp

  and 0xfffffff0, %esp

  pushl %ebp              

  pushl %ebx
  pushl %ecx
  pushl %edx

 
   movw    0x0c(%ebp) , %cx       # 15
   movw     0x8(%ebp),  %bp       #  movw  $message, %bp
  movw $0x1301, %ax
  movw $0x000c, %bx
  movw  $0x0,   %dx

  int $0x10

   popl %edx
   popl %ecx
   popl %ebx

  popl %ebp

#   movl %ebp, %esp   
#   popl %ebp
   leavel
   retl


.org  .+0x40
stack:


.code32
protcseg:
 
     sti


     movw  $0x10,  %ax
     movw %ax, %ds        # this is indispensable


######### return to real mode ######
.code16gcc
     cli

     movl   %cr0,  %eax
     andl    $0xfffffffe , %eax
     movl   %eax, %cr0



#DATA32 ADDR32
     jmp     $0x0, $write_vram    #ljmp $0x08, $write_vram #jmp  write_vram

####################################
.code32
gdt:   .word 0,0,0,0
    .word  0xffff
    .word  0x0000
    .word  0x9a00
    .word  0x00cf

    .word  0xffff
    .word  0x0000
    .word  0x9200
    .word  0x00cf

#    .word  0xffff
#    .word  0x0000
#    .word  0x9200
#    .word  0xe0cf

      .word 0,0,0,0  
#      .word 0,0,0,0  

gdt_48:    .word  0x1f
           .long  gdt
 

__asm__(".code32\n");


void display_str(char* str, short length);

int number ;
int number2;

void main2()
{
   char* str;

   number2 = number;
      char* pAddress = (char*)0xe0000000;
      pAddress +=300*800 + 100*3;
      for(int i = 0; i < 2400-200*3; i++)   
      {
         *pAddress = 255;
	 pAddress += 1;
      }
      while(1)
	 ;
}