《操作系统真相还原》——加载器

显存

将上一章的中断输出，变为显存输出

加载器

使用mbr引导程序从磁盘中加载loader程序。

MBR

%include "boot.inc"
SECTION MBR vstart=0x7c00         
   mov ax,cs      
   mov ds,ax
   mov es,ax
   mov ss,ax
   mov fs,ax
   mov sp,0x7c00
   mov ax,0xb800
   mov gs,ax


;clear screen
   mov     ax, 0x600
   mov     bx, 0x700
   mov     cx, 0          
   mov     dx, 0x184f	  
			  
			  
   int     0x10            ; int 0x10
	mov eax, LOADER_START_SECTION
	mov cx,1
	mov bx, LOADER_BASE_ADDR
call rd_disk_m_16 ; read data from disk
  jmp LOADER_BASE_ADDR
rd_disk_m_16:
  	mov esi, eax
	mov di, cx

	mov dx, 0x1f2
	mov al, cl
	out dx, al
	
	mov eax, esi

	mov dx, 0x1f3
	out dx, al

	mov cl, 8
	shr eax, cl
	mov dx, 0x1f4
	out dx,al

	shr eax, cl
	mov dx, 0x1f5
	out dx, al

	shr eax, cl
	and al, 0x0f
	or al, 0xe0
	mov dx, 0x1f6
	out dx, al

	mov al, 0x20
	mov dx, 0x1f7
	out dx, al

	
	
.not_ready:
	nop
	in al, dx
	and al, 0x88
	cmp al, 0x08
	jnz .not_ready


	mov ax, di
	mov dx, 256
	mul dx
	mov cx, ax
	mov dx, 0x1f0
.go_on_read:
	in ax, dx
	mov [bx], ax
	add bx, 2
	loop .go_on_read

	ret	 
   times 510-($-$$) db 0
   db 0x55,0xaa

Loader

%include "boot.inc"
SECTION Loader vstart=LOADER_BASE_ADDR        
 mov byte [gs:0x00],'2'
 mov byte [gs:0x01],0xA4 

 mov byte [gs:0x02],' '
 mov byte [gs:0x03],0xA4

 mov byte [gs:0x04],'M'
 mov byte [gs:0x05],0xA4

 mov byte [gs:0x06],'B'
 mov byte [gs:0x07],0xA4

 mov byte [gs:0x08],'R'
 mov byte [gs:0x09],0xA4 
   jmp $