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[Nasm-users] Handling timer interrupt
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From: zak100 <zul...@ya...> - 2009-08-06 14:03:16
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Hi,
I am trying to handle timer interrupt in a OS like code. I have got a
bootloader whose code is given below and is working (I am able to see the
mesg at the start up):
%define bootseg 0
%define bootoff 7C00h
%define loadoff 7E00h
ORG 7c00h ;Because BIOS loades the OS at
; address 0:7C00h so ORG 7C00h
; makes that the refrence to date
; are with the right offset (7c00h).
; CS = 0 / IP = 7C00h // SS = ? / SP = ?
; You are now at address 7c00.
jmp start ;Here we start the, BIOS gave us now the control.
;///////////////////////////////////////////
;//Here goes all the data of the program.
;///////////////////////////////////////////
xCursor db 0
yCursor db 0
nSector db 0
nTrack db 0
nSide db 0
nDrive db 0
nTrays db 0
;
szReady db 'Are You Ready to start Loading the OS...',0
szErrorReadingDrive db 'Error Reading Drive, Press any Key to
reboot...',0
;//Done Reading a track.
szPlaceMarker db '~~~~',0
szDone db 'Done',0
pOS dw loadoff
;//Points to where to download the Operating System.
;/////////////////////////////////
;//Here the program starts.
;/////////////////////////////////
start:
CLI ;Clear Interupt Flag so while setting
;up the stack any interrupt would not be fired.
;----------------STACK
mov AX,7B0h ;lets have the stack start at 7c00h-256 = 7B00h
mov SS,ax ;SS:SP = 7B0h:256 = 7B00h:256
mov SP,256 ;Lets make the stack 256 bytes.
XOR AX,AX ;Makes AX=0.
MOV ES,AX ;Make ES=0
mov DS,ax
STI ;Set Back the Interupt Flag after
;we finished setting a stack frame.
Call ClearScreen ;ClearScreen()
LEA AX,[szReady] ;Get Address of szReady.
CALL PrintMessage ;Call PrintfMessage()
CALL GetKey ;Call GetKey()
mov bp, 1 ; sectors to load
CALL DownloadOS
; CALL GetKey ;Call GetKey()
CALL GiveControlToOS ;Give Control To OS.
;/////////////////////////////////////
;//Prints a message to the screen.
;/////////////////////////////////////
PrintMessage:
mov DI,AX ;AX holds the address of the string to Display.
Mov byte [xCursor],1 ;Column.
ContinuPrinting:
cmp byte [DI],0 ;Did we get to the End of String.
JE EndPrintingMessage ;if you get to the end of the string return.
mov AH,2 ;Move Cursor
mov DH,[yCursor] ;row.
mov DL,[xCursor] ;column.
mov BH,0 ;page number.
INT 10h
INC byte [xCursor]
mov AH,0Ah ;Display Character Function.
mov AL,[DI] ;character to display.
mov BH,0 ;page number.
mov CX,1 ;number of times to write character
INT 10h
INC DI ;Go to next character.
JMP ContinuPrinting ;go to Print Next Character.
EndPrintingMessage:
Inc byte [yCursor] ;So Next time the message would
;be printed in the second line.
cmp byte [yCursor],25
JNE dontMoveCorsurToBegin
Mov byte [yCursor],0
dontMoveCorsurToBegin:
ret
;PrintMessage EndP
;//////////////////////////////////////
;//Waits for the user to press a key.
;//////////////////////////////////////
GetKey: ; PROC
mov ah,0
int 16h ;Wait for a key press.
Ret
;///////////////////////////////////////////
;//Gives Control To Second Part Loader.
;///////////////////////////////////////////
GiveControlToOS:
LEA AX,[szDone]
Call PrintMessage
CALL GetKey
jmp 7E0h:40h
mov ax, [loadoff + 18h]
push 7E0h
push ax
retf
;///////////////////////////////////
;//Clear Screen.
;///////////////////////////////////
ClearScreen:
mov ax,0600h ;//Scroll All Screen UP to Clear Screen.
mov bh,07
mov cx,0
mov dx,184fh
int 10h
Mov byte [xCursor],0 ;//Set Cursor Position So next
;//write would start in
;//the beginning of screen.
Mov byte [yCursor],0
Ret
;/////////////////////////////////
;//PrintPlaceMarker.
;/////////////////////////////////
PrintPlaceMarker:
LEA AX,[szPlaceMarker]
CALL PrintMessage ;Call PrintfMessage()
; CALL GetKey ;Call GetKey()
ret
;///////////////////////////////////
;//DownloadOS
;///////////////////////////////////
DownloadOS:
mov byte [nDrive],0
mov byte [nSide],0
mov byte [nTrack],0
mov byte [nSector],1 ; desired sector - 1!
ContinueDownload:
INC byte [nSector] ;Read Next Sector.
cmp byte [nSector],19 ;Did we get to end of track.
JNE StayInTrack
CALL PrintPlaceMarker ;Print now '~~~~' so the user would
;know that we finished reading a track
INC byte [nTrack] ;If we get to end of track Move to
next track.
mov byte [nSector],1 ;And Read Next Sector.
CMP byte [nTrack],5 ;Read 5 Tracks (Modify this value
;to how much Tracks you want to read).
JE EndDownloadingOS
StayInTrack:
;ReadSector();
Call ReadSector
dec bp
jz EndDownloadingOS
JMP ContinueDownload
;If didn't yet finish Loading OS.
EndDownloadingOS:
ret
;////////////////////////////////////////
;//Read Sector.
;////////////////////////////////////////
ReadSector:
mov byte [nTrays],0
TryAgain:
mov AH,2 ;//Read Function.
mov AL,1 ;//1 Sector.
mov CH,[nTrack]
mov CL,[nSector] ;//Remember: Sectors start with 1, not 0.
mov DH,[nSide]
mov DL,[nDrive]
Mov BX,[pOS] ;//ES:BX points to the address
;to were to store the sector.
INT 13h
jnc EndReadSector
mov AH,0 ;Else Reset Drive . And Try Again...
INT 13h
cmp byte [nTrays],3 ;Check if you tryed reading
;more then 3 times.
JE DisplayError ; if tryed 3 Times Display Error.
INC byte [nTrays]
jmp TryAgain ;Try Reading again.
DisplayError:
LEA AX,[szErrorReadingDrive]
Call PrintMessage
Call GetKey
mov AH,0 ;Reboot Computer.
INT 19h
EndReadSector:
ADD WORD [pOS],512 ;//Move the pointer
;(ES:BX = ES:pOS = 0:pOS) 512 bytes.
;//Here you set the varible
;pOS (pOS points to were BIOS
;//Would load the Next Sector).
Ret
;////////////////////////////////////
;//
;////////////////////////////////////
times 510 - ($ - $$) db 0
db 55h, 0AAh
;-------------------
An then I have a kernel code which includes a file also:
%include "lib.inc"
mov ax, 7E0H
mov ds,ax
mov es,ax
mov si, msg
mov ah, 0Eh
mov bx, 7
top:
lodsb
cmp al, 0
jz blackhole1
int 10h
jmp short top
blackhole1:install 6
blackhole:
hlt
jmp blackhole
msg db 'Welcome to the Kernel!', 0
msgA db 'Total minutes elapsed since Kernel start is', 0AH, 0DH
clkcounter db 0
secs db 0
mins db 0
times 0x200-($-$$) db 0
The include file is given below:
%macro install 1
push ax
mov al,%1
mov ah, 0eh
int 10h
pop ax
;push ds
;mov ax, 0
;mov word[%1*4],isr_add
;mov word[%1*4+2],cs
;pop ds
%endmacro
isr_add:
cli
inc byte [byte cs:clkcounter]
cmp byte [byte cs:clkcounter],18
jz handle_secs
sti
iret
handle_secs:
mov byte [byte cs:clkcounter],0
inc byte [byte cs:secs]
cmp byte [byte cs:secs],60
jz handle_mins
sti
iret
handle_mins:
mov byte [byte cs:secs],0
inc byte [byte cs:mins]
push ds
push es
xor ax,ax
mov ds,ax
mov es,ax
; should probably set up a sane stack here, too.
mov si,msgA ; "our dear string"
;mov bx,7
mov ah,0Eh
msgloop:
lodsb
or al,al
jz end44
int 10h ; since we're still in RM, we can use bios.
jmp msgloop
end44: pop es
pop ds
sti
iret
sti
iret
For compilation I am using following commands:
nasm -f bin bootmz.asm -o boot.bin
nasm -f obj test_k.asm
alink -oEXE test_k.obj
copy /b boot.bin+test_k.exe image.bin
partcopy image.bin 0 323 -f0
Can somebody plz help me with this?
Zulfi.
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