; micro-os_kernel.asm
name "kernel"
; this is a very basic example
; of a tiny operating system.
;
; this is kernel module!
;
; it is assumed that this machine
; code is loaded by 'micro-os_loader.asm'
; from floppy drive from:
; cylinder: 0
; sector: 2
; head: 0
;=================================================
; how to test micro-operating system:
; 1. compile micro-os_loader.asm
; 2. compile micro-os_kernel.asm
; 3. compile writebin.asm
; 4. insert empty floppy disk to drive a:
; 5. from command prompt type:
; writebin loader.bin
; writebin kernel.bin /k
;=================================================
; directive to create bin file:
#make_bin#
; where to load? (for emulator. all these values are saved into .binf file)
#load_segment=0800#
#load_offset=0000#
; these values are set to registers on load, actually only ds, es, cs, ip, ss, sp are
; important. these values are used for the emulator to emulate real microprocessor state
; after micro-os_loader transfers control to this kernel (as expected).
#al=0b#
#ah=00#
#bh=00#
#bl=00#
#ch=00#
#cl=02#
#dh=00#
#dl=00#
#ds=0800#
#es=0800#
#si=7c02#
#di=0000#
#bp=0000#
#cs=0800#
#ip=0000#
#ss=07c0#
#sp=03fe#
; this macro prints a char in al and advances
; the current cursor position:
putc macro char
push ax
mov al, char
mov ah, 0eh
int 10h
pop ax
endm
; sets current cursor position:
gotoxy macro col, row
push ax
push bx
push dx
mov ah, 02h
mov dh, row
mov dl, col
mov bh, 0
int 10h
pop dx
pop bx
pop ax
endm
print macro x, y, attrib, sdat
LOCAL s_dcl, skip_dcl, s_dcl_end
pusha
mov dx, cs
mov es, dx
mov ah, 13h
mov al, 1
mov bh, 0
mov bl, attrib
mov cx, offset s_dcl_end - offset s_dcl
mov dl, x
mov dh, y
mov bp, offset s_dcl
int 10h
popa
jmp skip_dcl
s_dcl DB sdat
s_dcl_end DB 0
skip_dcl:
endm
; kernel is loaded at 0800:0000 by micro-os_loader
org 0000h
; skip the data and function delaration section:
jmp start ; first byte of this jump instruction is 0E9h it is
; used by loader to determine if we had a sucessful launch.
;==== data section =====================
; welcome message:
msg db 'welcome to micro-os!', 0
cmd_size equ 10 ; size of command_buffer
command_buffer db cmd_size dup('b')
clean_str db cmd_size dup(' '), 0
prompt db '>', 0
; commands:
chelp db 'help', 0
chelp_tail:
ccls db 'cls', 0
ccls_tail:
cquit db 'quit', 0
cquit_tail:
cexit db 'exit', 0
cexit_tail:
creboot db 'reboot', 0
creboot_tail:
help_msg db 'thank you for using micro-os!', 0Dh,0Ah
db 'list of supported commands:', 0Dh,0Ah
db 'help - print out this list.', 0Dh,0Ah
db 'cls - clear the screen.', 0Dh,0Ah
db 'reboot - reboot the machine.', 0Dh,0Ah
db 'quit - same as reboot.', 0Dh,0Ah
db 'exit - same as quit.', 0Dh,0Ah
db 'more to come!', 0Dh,0Ah, 0
unknown db 'unknown command: ' , 0
;======================================
start:
; set data segment:
push cs
pop ds
; set default video mode 80x25:
mov ah, 00h
mov al, 03h
int 10h
; blinking disabled for compatibility with dos/bios,
; emulator and windows prompt never blink.
mov ax, 1003h
mov bx, 0 ; disable blinking.
int 10h
; clear screen:
call clear_screen
; print out the message:
lea si, msg
call print_string
eternal_loop:
call get_command
call process_cmd
; make eternal loop:
jmp eternal_loop
;===========================================
get_command proc near
; set cursor position to bottom
; of the screen:
mov ax, 40h
mov es, ax
mov al, es:[84h]
gotoxy 0, al
; clear command line:
lea si, clean_str
call print_string
gotoxy 0, al
; show prompt:
lea si, prompt
call print_string
; wait for a command:
mov dx, cmd_size ; buffer size.
lea di, command_buffer
call get_string
ret
get_command endp
;===========================================
process_cmd proc near
;//// check commands here ///
; set es to ds
push ds
pop es
cld ; forward compare.
; compare command buffer with 'help'
lea si, command_buffer
mov cx, chelp_tail - offset chelp ; size of ['help',0] string.
lea di, chelp
repe cmpsb
je help_command
; compare command buffer with 'cls'
lea si, command_buffer
mov cx, ccls_tail - offset ccls ; size of ['cls',0] string.
lea di, ccls
repe cmpsb
jne not_cls
jmp cls_command
not_cls:
; compare command buffer with 'quit'
lea si, command_buffer
mov cx, cquit_tail - offset cquit ; size of ['quit',0] string.
lea di, cquit
repe cmpsb
je reboot_command
; compare command buffer with 'exit'
lea si, command_buffer
mov cx, cexit_tail - offset cexit ; size of ['exit',0] string.
lea di, cexit
repe cmpsb
je reboot_command
; compare command buffer with 'reboot'
lea si, command_buffer
mov cx, creboot_tail - offset creboot ; size of ['reboot',0] string.
lea di, creboot
repe cmpsb
je reboot_command
;////////////////////////////
; if gets here, then command is
; unknown...
mov al, 1
call scroll_t_area
; set cursor position just
; above prompt line:
mov ax, 40h
mov es, ax
mov al, es:[84h]
dec al
gotoxy 0, al
lea si, unknown
call print_string
lea si, command_buffer
call print_string
mov al, 1
call scroll_t_area
jmp processed
; +++++ 'help' command ++++++
help_command:
; scroll text area 9 lines up:
mov al, 9
call scroll_t_area
; set cursor position 9 lines
; above prompt line:
mov ax, 40h
mov es, ax
mov al, es:[84h]
sub al, 9
gotoxy 0, al
lea si, help_msg
call print_string
mov al, 1
call scroll_t_area
jmp processed
; +++++ 'cls' command ++++++
cls_command:
call clear_screen
jmp processed
; +++ 'quit', 'exit', 'reboot' +++
reboot_command:
call clear_screen
print 5,2,0011_1111b," please eject any floppy disks "
print 5,3,0011_1111b," and press any key to reboot... "
mov ax, 0 ; wait for any key....
int 16h
; store magic value at 0040h:0072h:
; 0000h - cold boot.
; 1234h - warm boot.
mov ax, 0040h
mov ds, ax
mov w.[0072h], 0000h ; cold boot.
jmp 0ffffh:0000h ; reboot!
; ++++++++++++++++++++++++++
processed:
ret
process_cmd endp
;===========================================
; scroll all screen except last row
; up by value specified in al
scroll_t_area proc near
mov dx, 40h
mov es, dx ; for getting screen parameters.
mov ah, 06h ; scroll up function id.
mov bh, 07 ; attribute for new lines.
mov ch, 0 ; upper row.
mov cl, 0 ; upper col.
mov di, 84h ; rows on screen -1,
mov dh, es:[di] ; lower row (byte).
dec dh ; don't scroll bottom line.
mov di, 4ah ; columns on screen,
mov dl, es:[di]
dec dl ; lower col.
int 10h
ret
scroll_t_area endp
;===========================================
; get characters from keyboard and write a null terminated string
; to buffer at DS:DI, maximum buffer size is in DX.
; 'enter' stops the input.
get_string proc near
push ax
push cx
push di
push dx
mov cx, 0 ; char counter.
cmp dx, 1 ; buffer too small?
jbe empty_buffer ;
dec dx ; reserve space for last zero.
;============================
; eternal loop to get
; and processes key presses:
wait_for_key:
mov ah, 0 ; get pressed key.
int 16h
cmp al, 0Dh ; 'return' pressed?
jz exit
cmp al, 8 ; 'backspace' pressed?
jne add_to_buffer
jcxz wait_for_key ; nothing to remove!
dec cx
dec di
putc 8 ; backspace.
putc ' ' ; clear position.
putc 8 ; backspace again.
jmp wait_for_key
add_to_buffer:
cmp cx, dx ; buffer is full?
jae wait_for_key ; if so wait for 'backspace' or 'return'...
mov [di], al
inc di
inc cx
; print the key:
mov ah, 0eh
int 10h
jmp wait_for_key
;============================
exit:
; terminate by null:
mov [di], 0
empty_buffer:
pop dx
pop di
pop cx
pop ax
ret
get_string endp
; print a null terminated string at current cursor position,
; string address: ds:si
print_string proc near
push ax ; store registers...
push si ;
next_char:
mov al, [si]
cmp al, 0
jz printed
inc si
mov ah, 0eh ; teletype function.
int 10h
jmp next_char
printed:
pop si ; re-store registers...
pop ax ;
ret
print_string endp
; clear the screen by scrolling entire screen window,
; and set cursor position on top.
; default attribute is set to white on blue.
clear_screen proc near
push ax ; store registers...
push ds ;
push bx ;
push cx ;
push di ;
mov ax, 40h
mov ds, ax ; for getting screen parameters.
mov ah, 06h ; scroll up function id.
mov al, 0 ; scroll all lines!
mov bh, 1001_1111b ; attribute for new lines.
mov ch, 0 ; upper row.
mov cl, 0 ; upper col.
mov di, 84h ; rows on screen -1,
mov dh, [di] ; lower row (byte).
mov di, 4ah ; columns on screen,
mov dl, [di]
dec dl ; lower col.
int 10h
; set cursor position to top
; of the screen:
mov bh, 0 ; current page.
mov dl, 0 ; col.
mov dh, 0 ; row.
mov ah, 02
int 10h
pop di ; re-store registers...
pop cx ;
pop bx ;
pop ds ;
pop ax ;
ret
clear_screen endp
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