micro-os_loader.asm

一个模拟的操作系统的一些功能

; This is a very basic example
; of a tiny Operating System.

; Directive to create BOOT file:
   #MAKE_BOOT#

; This is an OS loader only!
;
; It can be loaded at the first
; sector of a floppy disk:
;   cylinder: 0
;   sector: 1
;   head: 0
;
; The code in this file is supposed
; to load the Kernel (micro-os_kernel.asm)
; and to pass control over it.
; The Kernel code should be on floppy at:
;   cylinder: 0
;   sector: 2
;   head: 0

; Memory table (hex):
; -------------------------------
; 07C0:0000 |   Boot Sector
; 07C0:01FF |   (512 bytes)
; -------------------------------
; 07C0:0200 |    Stack
; 07C0:03FF |   (255 words)
; -------------------------------
; 0800:0000 |    Kernel
; 0800:1400 | 
;           |   (currently 5 Kb,
;           |    10 sectors are
;           |    loaded from
;           |    floppy)
; -------------------------------

; micro-os_loader.asm file produced by
; this code should be less or
; equal to 512 bytes, since this
; is the size of the boot
; sector!
; Current version is compiled to
; 101 bytes.


include 'emu8086.inc'

; Boot record is loaded at 0000:7C00
ORG 7C00h

; skip the data section:
JMP start

;==== data section =====================

; welcome message:
msg  DB 'Welcome to micro-os', 13, 10,
     DB 'Loading...', 0

;======================================

start:

; initialize the stack:
MOV     AX, 07C0h
MOV     SS, AX
MOV     SP, 03FEh ; top of the stack.


; set Data Segment:
PUSH    CS
POP     DS

; set default video mode 80x25:
MOV     AH, 00h
MOV     AL, 03h
INT     10h

; print welcome message:
LEA     SI, msg
CALL    print_string

;===================================
; load the Kernel at 0800h:0000h
; 10 sectors starting at:
;   cylinder: 0
;   sector: 2
;   head: 0

; BIOS passes drive number in DL,
; so it's not changed:

MOV     AH, 02h ; read function.
MOV     AL, 10  ; sectors to read.
MOV     CH, 0   ; cylinder.
MOV     CL, 2   ; sector.
MOV     DH, 0   ; head.
; DL not changed! - drive number.

; ES:BX points to receiving
;  data buffer:
MOV     BX, 0800h   
MOV     ES, BX
MOV     BX, 0

; read!
INT     13h
;===================================

; pass control to Kernel:
JMP     0800h:0000h

;===========================================

DEFINE_PRINT_STRING

END