realinit.asm

自己动手写操作系统源代码,不可多得的代码

;;------------------------------------------------------------------------
;;  Original Author           : Garry
;;  Original Finished date    :
;;  FileName                  : realinit.asm
;;  Procedure defined         :
;;                              1.np_printmsg
;;                              2.
;;                              3.
;;                              4.
;;                              5.
;;  Last modified date        :
;;  Last modified author      :
;;  Lines Number              :
;;  Function                  :
;;                              This module countains the real mode initia-
;;                              lize code.
;;                              These code initialize the CPU context,CRT
;;                              dis play,Flopy disk controller,8259 chip,etc.
;;------------------------------------------------------------------------

    bits 16                      ;;The real mode code.

    org 0x0000
    ;org 0x0100                   ;;------------ ** debug ** --------------

    %define DEF_RINIT_START 0x01000  ;;Start address of this module.
                                     ;;This code is loaded into memory by
                                     ;;boot sector,and resides at 0x01000.

    %define DEF_MINI_START  0x02000  ;;The start address of the mini-kernal
                                     ;;when it be loaded into memory.

gl_initstart:
    mov ax,DEF_RINIT_START       ;;The following code prepare the execute
                                 ;;context.
    shr ax,4
    mov ds,ax
    mov es,ax
    mov ss,ax
    mov sp,0x0fff

    mov ax,okmsg
    call np_strlen
    mov ax,okmsg
    call np_printmsg
    mov ax,initmsg
    call np_strlen
    mov ax,initmsg
    call np_printmsg

    ;;The following code initializes the system hardware.

    call np_init_crt             ;;Initialize the crt display.
    call np_init_keybrd          ;;Initialize the key board.
    call np_init_dmac            ;;Initialize the DMA controller.
    call np_init_8259            ;;Initialize the interrupt controller.
    call np_init_clk             ;;Initialize the clock chip.
    call np_get_syspara          ;;Gather the system parameters.

    ;;Now,we have finished intialize the system hardware,it's time to enter
    ;;protected mode.

    call np_act20addr            ;;First,activate the above 12 address lines.

    xor eax,eax
    mov ax,ds
    shl eax,0x04
    add eax,gl_gdt_content       ;;Form the line address of the gdt content.
    mov dword [gl_gdt_base],eax
    lgdt [gl_gdt_ldr]            ;;Now,load the gdt register.

    mov ax,okmsg                 ;;--------- ** debug ** -----------------
    call np_strlen
    mov ax,okmsg
    call np_printmsg
    ;call np_write_mem
    ;mov ax,gl_mem_content
    ;mov cx,0x08
    ;call np_printmsg

    mov eax,cr0
    or eax,0x01                  ;;Set the PE bit of CR0 register.
    mov cr0,eax                  ;;Enter the protected mode.

    ;mov ax,0x010                 ;;The following code reinitialize the segme-
                                 ;;nt registers.
    ;mov ds,ax
    ;mov es,ax
    ;mov fs,ax
    ;mov gs,ax

    jmp dword 0x08 : DEF_MINI_START  ;;Transant the control to Mini Kernal.

    ;mov ax,0x4c00                ;;------------- ** debug ** -------------
    ;int 0x21                     ;;------------- ** debug ** -------------

;;------------------------------------------------------------------------
;;  Initialize procedures,including:
;;  1.np_act20addr       : Activate the above 12 address lines of the PC.
;;  2.np_init8259        : Initialize the 8259 chip.
;;------------------------------------------------------------------------

np_deadloop:                     ;;A dead loop procedure,is called by init-
                                 ;;ializing procedures,when these initialing
                                 ;;procedure are failed.
                                 ;;This procedure print out a message,and
                                 ;;enter into a dead loop.
                                 ;;The only way to recover from this dead
                                 ;;loop is cool restart your computer,because
                                 ;;of the shutting off of the interrupt.
    mov ax,errormsg
    call np_strlen
    mov ax,errormsg,
    call np_printmsg

    mov cx,0x01
.ll_dead:
    inc cx
    loop .ll_dead
    ret                          ;;The end of the procedure.

np_init_crt:
    ret                          ;;The end of the procedure.

np_init_keybrd:
    ret                          ;;The end of the procedure.

np_init_dmac:
    ret                          ;;The end of the procedure.

np_init_8259:
    ret                          ;;The end of the procedure.

np_init_clk:
    ret                          ;;The end of the procedure.
np_get_syspara:
    ret                          ;;The end of the procedure.


np_act20addr:                    ;;A procedure to activate the 20th address line.

                                 ;;In IBM-PC hardware,the above 12 address l-
                                 ;;ine,are firmed when computer restart,in o-
                                 ;;rder to access the whole 32 bit address s-
                                 ;;pace,we must activate the above 12 address
                                 ;;lines,which is begin at 20th line.
    call np_wait_8042free
    cmp cx,0x0000
    je .ll_error

    mov al,0x0D1
    mov dx,0x064
    out dx,al
    call np_wait_8042free
    cmp cx,0x0000
    je .ll_error
    mov al,0x0DF
    mov dx,0x060
    out dx,al
    jmp .ll_end
.ll_error:                       ;;An error occured,the 8042 input buffer is
                                 ;;always full,maybe hardware error.
    call np_deadloop             ;;End dead loop.
.ll_end:
    in al,0xee                   ;;Fuck code!!!!!
    in al,0xee
    in al,0xee
    in al,0xee

    in al,0x92
    or al,0x02
    out 0x92,al
    ret                          ;;The end of the procedure,np_act20addr

np_wait_8042free:                ;;This procedure test the 8042 input buffer
                                 ;;state,if full,return a failure value in cx,
                                 ;;otherwise,return non-zero in cx.
    mov cx,0xffff
.ll_begin:
    in al,0x64
    test al,0x02
    jnz .ll_begin
    ret                          ;;End of the procedure.


;;------------------------------------------------------------------------
;;  The following are some helper procedures.
;;  Including:
;;  1.np_printmsg       : print out some message,use ax and cx to trans pa-
;;                        rameters.
;;  2.np_strlen         : get the string's length,a zero indicates the end
;;                        of a string.Use ax as string's base address,and cx
;;                        as return value.
;;  3.
;;
;;------------------------------------------------------------------------

np_printmsg:                     ;;This procedure print out some message,
                                 ;;the ax register indicates the base address
                                 ;;of the string,and cx is the length of the
                                 ;;string.
                                 ;;CAUTION: After return,the ax register's
                                 ;;value may be changed.

    push bp                      ;;Save the registers used by this proc.
    push bx
    push ax                      ;;Some registers not used in this procedu-
                                 ;;re maybe used in the int 0x010,so we must
                                 ;;save them too.Fuck BIOS!!!!!
    push cx
    mov ah,0x03
    mov bh,0x00
    int 0x010                    ;;Read the position of cursor.
    mov bx,0x0007
    mov ax,0x1301
    pop cx
    pop bp
    int 0x010                    ;;Print out the the message.
    pop bx
    pop bp
    ret                          ;;End of the procedure.

np_strlen:                       ;;This procedure get a string's length.
                                 ;;A zero indicates the string's end,the
                                 ;;same as C string.
                                 ;;The ax countains the base address of
                                 ;;the string,and after return,the cx coun-
                                 ;;tains the result.
                                 ;;CAUTION: After return,the ax's value may
                                 ;;be changed.
    push bp
    push bx
    mov bx,ax
    mov al,0x00
    xor cx,cx
.ll_begin:
    cmp byte [bx],al
    je .ll_end
    inc bx
    inc cx
    jmp .ll_begin
.ll_end:
    pop bx
    pop bp
    ret                          ;;End of the string.

gl_datasection:
    okmsg      db 0x0d
               db 0x0a
               db 'OK!'
               db 0x00
    initmsg    db 0x0d
               db 0x0a
               db 'Initializing the hardware...'
               db 0x00
    errormsg   db 0x0d
               db 0x0a
               db 'Error: please restart your computer by manual(reset button)'
               db ',or power off it and power on again.'
               db 0x0d
               db 0x0a
               db 0x00
gl_gdt_content:                  ;;The GDT table content
               dd 0x00000000     ;;NULL GDT entry.
               dd 0x00000000
               dd 0x0000ffff     ;;Code segment GDT entry.
               dd 0x00cf9b00
               dd 0x0000ffff     ;;Data segment GDT entry.
               dd 0x00cf9300
gl_gdt_ldr:
               dw 8*3 - 1        ;;The GDT table's limit.
gl_gdt_base:
               dd 0x00000000     ;;The GDT table's line address,must initial-
                                 ;;ize it before lgdt instruction.
gl_mem_content:                  ;;--------------- ** debug ** -----------
               dd 0x00000000
               dd 0x00000000

np_write_mem:                    ;;--------------- ** debug ** -----------
    push ax
    push bx
    push cx
    push dx
    push si
    push di
    mov eax,dword [ds : 0x4668]
    mov di,gl_mem_content
    add di,0x07
    mov cx,0x08
    mov bl,0x0a
.ll_begin:
    mov bh,al
    and bh,0x0f
    cmp bh,bl
    jb .ll_isn
    sub bh,bl
    add bh,'a'
    mov byte [di],bh
    jmp .ll_continue
.ll_isn:
    add bh,'0'
    mov byte [di],bh
.ll_continue:
    shr eax,0x04
    dec di
    loop .ll_begin
    pop di
    pop si
    pop dx
    pop cx
    pop bx
    pop ax
    ret                          ;;End of the procedure.

gl_endof_module:
    times 4*1024 - ($ - $$) db 0x00