Assembly language - Wang Shuang Chapter 13 int instruction - Notes

Write interrupt routines that are called by the provider

Question 1 ： To write 、 Installation interrupted 7ch Interrupt routine for

function ： Seek one word Square of type data
Parameters ：（ax）= Data to be calculated
Return value ：dx、ax The high value of the results stored in 16 Bit and low 16 position
Application, for example, ： seek 2*3456^2

assume cs:code

code segment

	start:	mov ax, 3456		;(ax)=3456
			int 7ch				; Call interrupt 7ch Interrupt routine for , Calculation ax The square of the data in 
			add ax, ax
			adc dx, dx			;dx:ax Store results , Multiply the result by 2
			
			mov ax, 4c00h
			int 21h
			
code ends

end start

We need to do the following 3 Part of the work
（1） Write procedures to achieve the function of square ; Be careful ： At the end of the interrupt routine , To use iret Instructions .
（2） Erection sequence , Install it in the 0:200 It's about ;
（3） Set interrupt vector table , Save the entry address of the program in 7ch In table items , Make it an interruption 7ch Interrupt routine for .

assume cs:code

code segment

	start:	mov ax, cs
			mov ds, ax
			mov si, offset sqr ; Set up ds:si Specify the source address 
			
			mov ax, 0
			mov es, ax
			mov di, 200h
			
			mov cx, offset sqrend - offset sqr
			cld
			rep movsb
			
			mov ax, 0
			mov es, ax
			mov word ptr es:[7ch*4], 200h
			mov word ptr es:[7ch*4+2], 0
			
			mov ax, 4c00h
			int 21h
			
	sqr:	mul ax
			iret
			
	sqrend:	nop
			
code ends

end start

Question two ： To write 、 Installation interrupted 7ch Interrupt routine for

function ： Make one all letters , With 0 a null-terminated string , Convert to uppercase
Parameters ：ds:si Point to the first address of the string
Application, for example, ： take data The string in the section is converted to uppercase

assume cs:code

data segment
	db 'conversation', 0
data ends

code segment

	start:	mov ax, data
			mov ds, ax
			mov si, 0
			int 7ch
			
			mov ax, 4c00h
			int 21h
code ends

end start

The installation procedure is as follows ：

assume cs:code

data segment
	db 'conversation', 0
data ends

code segment

	start:	mov ax, cs
			mov ds, ax
			mov si, offset captical
			
			mov ax, 0
			mov es, ax
			mov di, 200h
			
			mov cx, offset capitalend - offset capital
			cld
			rep movsb
			
			mov ax, 0
			mov es, ax
			mov word ptr es:[7ch*4], 200h
			mov word ptr es:[7ch*4+2], 0
			
			mov ax, 4c00h
			int 21h
			
	captical:	push cx
				push si
	change:		mov cl, [si]
				mov ch, 0
				jcxz ok
				and byte ptr[si], 11011111b
				inc si
				jmp short change
	ok:			pop si
				pop cx
				iret
				
	capitalend:	nop
			
code ends

end start

In the interrupt routine capital Registers are used in si and cx, Writing interrupt routines has the same problem as writing subroutines , Is to avoid register conflicts . Attention should be paid to saving and restoring the values of registers used in the process .

Question two ： use 7ch Interrupt routine complete loop Function of instruction