head_test.asm

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 1 [bits 32]
 2 start_32:
 3     mov ax,0x10
 4     mov ds,ax
 5     mov word [gdtr],gdt_end-gdt
 6     mov dword [gdtr+2],gdt
 7     mov word [idtr],idt_end-idt
 8     mov dword [idtr+2],idt
 9     lgdt [gdtr]
10     lidt [idtr]
11     mov ax,0x10
12     mov ds,ax
13     mov es,ax
14     mov ss,ax        ; stack segment = data segment = code seg
15     mov sp,stack_top
16     mov ax,0x18
17     mov gs,ax
18     
19     call clr_scr
20     call welcome
21     
22     jmp $
23     
24 welcome:
25     mov esi,str_welcome
26     sub edi,edi
27     mov ah,0ch
28 rp_welcome:
29     mov al,[esi]
30     test al,al        ; al & al = 0 ?
31     jz end_welcome
32     mov [gs:edi],ax
33     inc esi
34     add edi,2
35     jmp rp_welcome
36 end_welcome:
37     ret
38 
39 clr_scr:
40     xor ah,ah
41     mov al,' '
42     mov ecx,2000
43     sub edi,edi
44 rp_clr:
45     mov [gs:edi],ax
46     add edi,2
47     dec ecx
48     jne rp_clr
49     ret
50 
51 
52     
53 ;---------------------------------------------------------------------
54 ;    data segment, ds:esi, r/w
55 ;    因为数据段和代码段重叠，而前面一部分已经被代码段覆盖，所以
56 ;    数据段str_welcome的地址不是 0，而是代码段地址结尾处。
57 ;    堆栈段包含在数据段中，即16MB的末尾部分。
58 ;    实际分布：代码段->数据段->堆栈段
59 
60 str_welcome:    db    "Hello, OS! Welcome to protected mode!",0
61 
62 align 2
63 gdt:    dw 0,0,0,0                        ; 256*4*2bytes = 2KB
64         dw 0x1000,0x0000,0x9a00,0x00c0    ; 16MB
65         dw 0x1000,0x0000,0x9200,0x00c0
66         dw 0x0002,0x8000,0x920b,0x00c0
67         times (256-4) dw 0,0,0,0
68 gdt_end:
69 
70 idt:    times 256 dw 0,0,0,0            ; 256 interrupts
71 idt_end:
72 
73 gdtr:    dw 0,0,0
74 align 2
75 idtr:    dw 0,0,0
76 
77 ;---------------------------------------------------------------------
78 ;    stack segment
79 
80 stack_buttom:    times 512 dw 0    ;1KB
81 stack_top:

 

 

posted @ 2012-07-03 13:29  jinfengswust  阅读(129)  评论(0)    收藏  举报