os/kernel.asm at master · samg31/os · GitHub

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;kernel.asm
;Michael Black, 2007

;kernel.asm contains assembly functions that you can use in your kernel

	.global _putInMemory
	.global _interrupt
	.global _makeInterrupt21
	.extern _handleInterrupt21

;void putInMemory (int segment, int address, char character)
_putInMemory:
	push bp
	mov bp,sp
	push ds
	mov ax,[bp+4]
	mov si,[bp+6]
	mov cl,[bp+8]
	mov ds,ax
	mov [si],cl
	pop ds
	pop bp
	ret

;int interrupt (int number, int AX, int BX, int CX, int DX)
_interrupt:
	push bp
	mov bp,sp
	push ds		;use self-modifying code to call the right interrupt
	mov ax,[bp+4]	;get the interrupt number in AL
	mov bx,cs
	mov ds,bx
	mov si,#intr
	mov [si+1],al	;change the 00 below to the contents of AL
	pop ds
	mov ax,[bp+6]	;get the other parameters AX, BX, CX, and DX
	mov bx,[bp+8]
	mov cx,[bp+10]
	mov dx,[bp+12]

intr:	int #0x00	;call the interrupt (00 will be changed above)

	mov ah,#0	;we only want AL returned
	pop bp
	ret

;void makeInterrupt21()
;this sets up the interrupt 0x21 vector
;when an interrupt 0x21 is called in the future,
;_interrupt21ServiceRoutine will run

_makeInterrupt21:
	;get the address of the service routine
	mov dx,#_interrupt21ServiceRoutine
	push ds
	mov ax, #0	;interrupts are in lowest memory
	mov ds,ax
	mov si,#0x84	;interrupt 0x21 vector (21 * 4 = 84)
	mov ax,cs	;have interrupt go to the current segment
	mov [si+2],ax
	mov [si],dx	;set up our vector
	pop ds
	ret

;this is called when interrupt 21 happens
;it will call your function:
;void handleInterrupt21 (int AX, int BX, int CX, int DX)
_interrupt21ServiceRoutine:
	push dx
	push cx
	push bx
	push ax
	call _handleInterrupt21
	pop ax
	pop bx
	pop cx
	pop dx
	iret