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flat assembler > OS Construction > Calling real mode interrupts from protected mode

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Gomer73



Joined: 29 Nov 2003
Posts: 151
Heres a litte program I made up to call real mode interrupts from protected mode.

Was pretty tough to debug, but it is the basis for my new OS. Didn't see any examples anywhere of how to do it. I guess I could have made the IDT a 16 bit segment which would have saved some code(oh well).

Compile it as an .exe and run it from dos.

Basically the first digit on the screen toggles whenever an interrupt is being serviced. The second digit is toggled by my protected mode program.

Press caps lock to see that the real mode still works(or any other TSR's you might have loaded). Press left shift key to exit to dos.


Description: File OS
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Filename: FOS.ASM
Filesize: 6.6 KB
Downloaded: 307 Time(s)

Post 04 May 2004, 20:35
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
Nice bit of code Gomer73, Just what i'v been looking for, Can i use some of this code in my OS Question .
I can exchange it for my atapi driver Smile
ASHLEY4.
Post 05 May 2004, 17:49
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Gomer73



Joined: 29 Nov 2003
Posts: 151
Thanks, go for it, use the code for whatever you like.

I guess the code would be classified as public domain, which would mean no credit required and can be used under any kind of license.

I would love to have a look at your ATAPI code.

What are some of the specifications of the OS you are building?

One thing to not with the interrupt routine. The DS has to be initialized to a base 0 in order for it to work. The push DWORD [0] uses the ds, so no big deal since my DS in protected mode is set to base 0. However if the DS in protected mode is set to something else, you need to initialize the DS to 0 before the push.

Here is a modified source code to kind of do a work around for interrupts that require the DS to be set to something. It basically prints a message, waits for a key to be pressed, loads a file and then displays another message.

...Gomer73


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Filename: fos.ZIP
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Post 05 May 2004, 19:21
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
Thank Gomer73 Very Happy , My os is just some test code for a Os i'm making ,this is the spek.
It is loaded from the disk by a boot loader that loads a exe from the floppy, It does these things, Gets the address(as in port) of the first HD and the first CD/DVD, check for vesa,
does the a20, remap pic sets GDT,IDT,IT AS A CD/DVD driver with built in cdplayer,a simple keyboard,bmp viwer,time/date, it run's in ring0,it has functions for printing,hex,vesa fonts , put pixel.
Alot of the code is not the best,but at least it works.
Its made with fasm and is my first bit of code with fasm,
You get the whole os called "TestOs.zp" from my temp web site.
http://www.falconrybells.co.uk/
Theres also a game in asm (tasm) i made on there.

Thanks again
ASHLEY4.
Post 06 May 2004, 04:11
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Gomer73



Joined: 29 Nov 2003
Posts: 151
Nice program, works well(after I read the documentation more clearly).

Good organization and documentation as well.

I like small OS's. It makes it easier to understand whats happening. Would it be OK if I used some of your code and if so under what license? Licenses are kind of a weird thing for me. When I release my OS I don't think I will make it GPL because I don't want to restrict people from making stuff because they don't want to share their code.

All the best to you with the rest of your OS.

...Gomer73
Post 08 May 2004, 00:14
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
Thank's Gomer73,
You can use any part of the code as you like, But if you could just acknowledge the name's that are in the kernel32.asm file, Then the license is up to you.
I tryed to make it so most of the important bit's are in include file's, So people can understand a bit at a time like "A20.inc" etc.
My aim is to make a simple 32bit os, with no protection (runs in ring0) ,nopaging (If we keep things small,no need for virtual memory) and calls in stead of int's (should be much faster), Like a 32bit pmode dos with a flat memory model.
It will be cli or menu ,rather than a windows type gui.

If you want ,We could help one another with our OS's, as you seem to know fasm much better than me.

PS: The code was just put in a zip file as it was,So it could be better commented.
I have also made a iso, That you can burn on a cd,This is good as no floppy is needed,I can put it on my site if you are interested,or you need to no how it's done Let me know.

ASHLEY4.
Post 08 May 2004, 02:34
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Gomer73



Joined: 29 Nov 2003
Posts: 151
Would be glad to help out.
Time is the big thing for me. Tough to work on an OS, work, and have another additional hobby.

I am currently working on a pretty robust keyboard driver. I think it should fulfill all the needs. Supports unicode as well as getting the ascii value and key pressed. Currently right now I think too many OS's get stumped once the the key codes get to be more than one byte. It took some thinking, but I got away around that. Completely programmable by the user so that each key pressed will do 1 of several actions. The actions are as follows:

1. Send and 16 bit ascii code.
2. Toggle a mode(caps lock, num lock)
3. Set/release a mode(shift key, control key)
4. Run a program

When a key code is pressed that the keyboard table doesn't recognize, it prompts the user as to what key was pressed and what action to take.

It would be nice to build the two OS's together. Mine would include a GUI. Mainly because it is easier to multi-task(run calc and notepad for example). But I also like to be able to easily switch between GUI and Text mode.

Got it working without the ISO, so no need, but thanks.
Post 09 May 2004, 20:35
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
The keyboard drive sounds great,The keyboard in the zip file is only temp, But in the keyboard driver is a var that switch's the keyboard into a GAMES keyboard, So that up to 128 keys can be pressed at the same time and be registered as a press or as a release on releasing .
This is a good feature, For people who want to make game for your OS Smile .

ASHLEY4.
Post 10 May 2004, 15:06
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Gomer73



Joined: 29 Nov 2003
Posts: 151
That is a good idea, knowing whether a key is currently down or not is a good idea.
Too bad keyboard design doesn't allow multiple keys at the same time. I think certain key combinations won't register.
Post 10 May 2004, 15:34
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
THEY DO ,That's what the game keyboard does, upto 128 of them.
I can give you demo code for you to test if you like.
ASHLEY4.
Post 10 May 2004, 17:09
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7373
Location: Kraków, Poland
Many (perhaps the most of) keyboards won't send you codes for any more key presses when there are already six or more keys pressed at the same time.
Post 10 May 2004, 17:25
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ASHLEY4



Joined: 28 Apr 2004
Posts: 376
Location: UK
Hi Privalov
This is some code useing it in a game, I,v not try it with 128 just assumed,So i will take your word Smile .
Code:

                         MOV     AL,09h                    ; Get INT 09h address
                         MOV     AH,35h
                         INT     21h
                         MOV     [oldint9],BX              ; Save it for later
                         MOV     [oldint9+2],ES
                         MOV     AL,09h                    ; Set new INT 09h
                         MOV     DX,OFFSET  Newint9        ; DS:DX = new interrupt
                         MOV     AH,25h
                         INT     21h
*****************************************************************
maingameloop:
                         call KeyPressed
                         """""""""""""
                         """"""""""""""
                         jmp maingameloopif not the end

                         call   ReStoreInt9

                         end!
******************************************************************
;------------------------------------------------------------------------------------------------
; Installs New Int9
;------------------------------------------------------------------------------------------------

Newint9                 PROC

                        PUSH     AX                        ; Push registers
                        PUSH     BX
                        PUSH     DS
                        ; CLI
                        MOV      AX,CS          
                        MOV      DS,AX
                        IN       AL,60h
                        MOV      BX,AX
                        AND      BX,007Fh                  ; switch high bit of BX to zero
                        AND      AL,80h                    ; check high bit of port value
                        JZ       Press         
Release:                                                   ; high bit = 1: "release" code
                        MOV      KeyDown[bx],00h           ; write 00 to "down" array element 
                        JMP      Done
Press:                                                     ; high bit = 0: "press" code 
                        MOV      KeyDown[bx],01h           ; write 01 to "down" array element
Done:
                        IN       AL,61h                    ; read port 61h, system ctrl port
                        MOV      AH,AL                     ; save value to AH
                        OR       AL,80h                    ; set top bit to "1" - reset kbd
                        OUT      61h,AL                    ; write out value to port
                        XCHG     AH,AL                     ; put original value back into AL 
                        OUT      61h,AL                    ; rewrite original value in AL
                        MOV      AL,20h                    ; generate End of Interrupt 
                        OUT      20h,AL
                        ;STI                  
                        POP      DS                        ; pop registers
                        POP      BX             
                        POP      AX
            
                        IRET

Newint9                 ENDP

;------------------------------------------------------------------------------------------------
; Check to see if keypressed
;------------------------------------------------------------------------------------------------
KeyPressed              PROC

                        TEST    [KeyDown+EscKey],1         ; Is ESC held down?
                        JNZ     Exit                       ; Yes, exit

                        TEST    [KeyDown+Q],1              ; Is Q down?
                        JZ      Next1                      ; No, continue
                        CMP     PadLY,2
                        JBE     Next1
                        sub     PADLY,2                     ; Yes, move left pad up; dec
Next1:
                        TEST    [KeyDown+A],1              ; Is A down?
                        JZ      Next2                      ; No, continue
                        CMP     PadLY,182
                        JAE     Next2
                        add     PADLY,2                    ; Yes, move left pad down;inc
Next2:
                        TEST    [KeyDown+Down],1           ; Is down arrow down?
                        JZ      Next3                      ; No, continue
                        CMP     PadRY,182
                        JAE     Next3
                        add     PADRY,2                    ; Yes, move right pad down;inc
Next3:
                        TEST    [KeyDown+Up],1             ; Is up arrow down?
                        JZ      Next4                      ; No, exit
                        CMP     PadRY,2
                        JBE     Next4
                        sub     PADRY,2                    ; Yes, move right pad up;dec
Next4:
                        TEST    [KeyDown+W],1
                        JZ      Next5
                        CMP     Ballx,30
                        JA      Next5
                        CMP     BallXstate,2
                        JE      Next5
                        MOV     Bstart,0
Next5:
                        TEST    [KeyDown+Left],1
                        JZ      Last1
                        CMP     Ballx,290
                        JB      Last1
                        CMP     BallXstate,1
                        JE      Last1
                        MOV     Bstart,0
                       
Last1:
                        RET

KeyPressed              ENDP
;------------------------------------------------------------------------------------------------
; Restores Int9
;------------------------------------------------------------------------------------------------

ReStoreInt9             PROC

                        MOV     AL,09h                    ; Restore original INT 09h
                        MOV     DX,[oldint9] 
                        MOV     DS,[oldint9+2]            ; Move old INT 09H pointer to DS:DX
                        MOV     AH,25h 
                        INT     21h

                        RET

ReStoreInt9             ENDP
:=============================data===================================

KeyDown                 DB      128 dup(0)

EscKey               EQU     1                          ; Escape key scancode
Up                       EQU     48h                        ; Up arrow
Down                  EQU     50h                        ; Down arrow
Left                      EQU     4Bh
Q                          EQU     10H
A                          EQU     1EH
W                         EQU     11h
oldint9                 DW      0,0

    


ASHLEY4.
Post 10 May 2004, 18:01
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Gomer73



Joined: 29 Nov 2003
Posts: 151
The limitation has more to do with the way the keyboard is wired rather than the communication protocol to the PC.

For example on my Fujitsu keyboard, if I hold down the a and z keys and try to press the x key it won't work. On my laptop this key combo does work but if I hold down the d and c keys and try pressing the v key, the v key won't display.

Just something to keep in mind when programming keyboard games.
Post 11 May 2004, 06:00
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DennisCGc



Joined: 03 May 2004
Posts: 24
Location: Zoetermeer, The Netherlands
Gomer73 wrote:
The limitation has more to do with the way the keyboard is wired rather than the communication protocol to the PC.

For example on my Fujitsu keyboard, if I hold down the a and z keys and try to press the x key it won't work. On my laptop this key combo does work but if I hold down the d and c keys and try pressing the v key, the v key won't display.

Just something to keep in mind when programming keyboard games.

Indeed, this is totally the keyboard its fault.
You also have some keyboards, that the key combo SPACE and LEFT ARROW don't support. Rolling Eyes
Post 11 May 2004, 13:54
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