hos3.s

用于汇编领域的,运用于OS的MAIN函数.基于硬件基础的源代码

.code16

.global  _start

_start:
        movw    $0x1000, %ax            # entry point of kernel
        movw    %ax, %ds                # set DS	
		movw    %ax, %es                # set es

 		call    screen_setup            # for 80 x 25 screen mode

		movw    $greet, %si

		call    print                   # print message

		# redirect keyboard interrupt
        mov     $0, %ax
		mov     %ax, %es
		lea     kbdisr, %ax
		mov     $36, %di
		cld
		stosw                           # addr of kbdisr stored to [36]
		mov     %cs, %ax
		stosw
lp:                                     # infinite loop
#hlt
		jmp     lp

# kbdisr is here

kbdisr:
		in      $0x60, %al
        movb    $0x51, %al
		movb    $0x0e, %ah
		int     $0x10
		movb    $0x20, %al
		out     %al, $0x20
		iret
														

#screen setup for 80 x 25 mode
screen_setup:
        movw    $0xb800, %ax
	    movw    %ax, %es
	    xorw    %di, %di
		movw    $0x1f20, %ax
        movw    $0x800, %cx
	    cld
		rep     stosw
		
		movb    $0x02, %ah
		xorw    %dx, %dx
		xorw    %bx, %bx
		int     $0x10															        
		ret
		

print:
		 movb    (%si), %al
		  cmpb    $0x00, %al
		  je      print_end
		   movb    $0x0e, %ah
		     xorw    %bx, %bx
			 int     $0x10
			 incw    %si
			 jmp     print
print_end:
        movb    $0x0e, %ah
		movb    $0x0d, %al      # CR
        xorw    %bx, %bx
        int     $0x10
		movb    $0x0a, %al      # LF
		int     $0x10

        ret

greet:
		.asciz  "Hello from hos2"