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assembler
Jacob Dawid
Member #4,045
November 2003
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hi @ all

How can I directly compile asm commands?

I tried it with asm("<command>");, but every time MingW complains that ( in this special case here following ), "mov has got too many parameters":

...
asm("mov ah, 4fh "); /* mode 13h */
asm("mov al, 02h ");
asm("mov bx, 104h");
asm("int 10h "); /* 10h */
...
asm("mov ah, 08h ");
asm("int 21h "); /* wait for keypress */
...

this should normally switch the screen mode to 320x200...

Can anybody help me?

X-G
Member #856
December 2000
avatar

GCC uses AT&T syntax. What you have there is Intel syntax.

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gillius
Member #119
April 2000

You won't be able to run that with mingw anyway. Mingw only generates Windows applications.

Gillius
Gillius's Programming -- http://gillius.org/

Jacob Dawid
Member #4,045
November 2003
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X-G

What exactly is AT&T syntax ( where are the differences, how does it look like )? thx for ur help

Radagar
Member #2,768
September 2002
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I don't have an answer for you (and I'm not X-G) but that sure sounds like a Google question to me.

------------
Radagar - So your vote is for A.D.H.D.?
Chris Katko - Well, that was uninten--ooh kitty!

X-G
Member #856
December 2000
avatar

Yes, Google is the answer. I can't possibly even begin to describe all the differences here.

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Jacob Dawid
Member #4,045
November 2003
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Ok thx anyway, at least I won't sit in front of my pc and ask myself what I might have to do thx again

Oscar Giner
Member #2,207
April 2002
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But anyway, gillius is right. Even if that would compile it won't run with mingw, because mingw is a windows compiler. You'll need a DOS compiler, like djgpp, but this compiler seems not to work propertly/at all under XP.

Bob
Free Market Evangelist
September 2000
avatar

On top of that, it's 16-bit real mode code, which will not run under DJGPP anyway, at least, not without some heavy hacking.

--
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[ -- All my signature links are 404 -- ]

gillius
Member #119
April 2000

Why do I have this bad feeling that this ASM code is directly related to the "let's make an API to replace D3D" post made earlier by the same poster.

Somehow I don't feel that the next generation to replace Direct3D lies in "13h" graphics modes.

Gillius
Gillius's Programming -- http://gillius.org/

Thomas Fjellstrom
Member #476
June 2000
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Quote:

GCC uses AT&T syntax. What you have there is Intel syntax.

These days GAS does both. Theres a command... Probably in tfm.

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Jacob Dawid
Member #4,045
November 2003
avatar

btw, this is just one available gfx mode, gillius... just laugh, but I don't really need your help, there are others that share my view

CGamesPlay
Member #2,559
July 2002
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The others won't work either ::)

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Jacob Dawid
Member #4,045
November 2003
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I will have a closer look on it, thx. I am posting this message from school and downloading files is forbidden. Unfortunately, I won't have oppportunity to take a closer look on it, but be sure I will do this when I got home this evening.

Evert
Member #794
November 2000
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Quote:

Somehow I don't feel that the next generation to replace Direct3D lies in "13h" graphics modes.

He's not even setting mode 13h (although his comment claims that he is) - he's setting a VESA mode.

Quote:

this should normally switch the screen mode to 320x200...

Not quite.
AH=4F/AL=02 is the VESA set video mode function, not the standard VGA set videomode function (Ah=0). Moreover, BX=104 selects a 1024x768 video mode. (Just checked against Ralph Brown's interrupt listing).

Videomode 13h is called 13h for a reason: it is the mode number passed to the VGA interrupt handler. You set it by

mov ax, 0013h
int 10h

Word of advice: learn what that code actually does before you try to use it. I could tell you that

mov ah, 05h
int 13h

is a bright idea, but you wouldn't want to do that without knowing what it did, would you? (Hint: DON'T try that!)

gillius
Member #119
April 2000

Jacob, not matter what you do, the API won't matter too much unless you implement hardware rendering, which is basically required these days for any serious work.

But that's not the real concern. You can't set 13h or VESA or whatever hardware graphics modes from inside a Win32 application, which is what mingw32 generates.

As I stated in another thread, if you want to implement a new API you need to do it as a wrapper around either D3D or OpenGL, or convince all hardware manufacturers to implement drivers for your API (you could provide a simple software driver or D3D/OGL wrapper for those who don't), but attempting to compete directly with D3D/OGL probably isn't going to work too well, so the wrapper option (as Allegro uses) will be your best bet if you are serious about making a new API.

EDIT: heh looked up that interrupt call... "Format Track" (of the hard drive)

Gillius
Gillius's Programming -- http://gillius.org/

Jacob Dawid
Member #4,045
November 2003
avatar

ok, evert, now I've set the VESA mode 1024x768...
I didn't actually knew what this code does exactly, I just had in mind that it switches to a graphics mode, I began to program in assembler a few weeks ago... but everyone was a beginner once :-) hey it seems that you know more about assembler,... erm, excuse me for that stupid question, but after I have set the graphics mode, how can I access the ( video ) memory?

gillius
Member #119
April 2000

Did you just set VESA mode from a Win32 executable (you initially said you were using mingw)? Can you even do that? I'd be absolutely floored if Win NT let you do that, and quite surprised even if Win9x let you do that.

Gillius
Gillius's Programming -- http://gillius.org/

Jacob Dawid
Member #4,045
November 2003
avatar

No, gillius, normally then you would get a general protection fault. I proceeded this code with debug... But according to your statement, is there any way to get around this?

Nah here you are, a tets program. 68 Bytes: Sets VESA mode 1024x768 and draws two lines with a simple putpixel-loop

Evert
Member #794
November 2000
avatar

Quote:

I didn't actually knew what this code does exactly, I just had in mind that it switches to a graphics mode, I began to program in assembler a few weeks ago...

That was my point. You're calling interrupts without knowing, or having verified, what they do. That is a very dangerous thing to do. Make sure you get a copy of the interrupt functions you want to use (hardcopy if you can get it) and read it before actually using it.

Quote:

but everyone was a beginner once :-)

Indeed. Once, I thought it'd be cool to figure out what all those nifty interrupts did and started calling them at random. Thank god I somehow managed to kill the DOS kernel, effectively disabeling all disk access and forcing me to reboot before I actually formatted my harddisk.
Morale: be careful and know what you're doing.

Quote:

hey it seems that you know more about assembler,...

I haven't really used it much for about six or seven years and I know next to nothing about protected mode.

Quote:

erm, excuse me for that stupid question, but after I have set the graphics mode, how can I access the ( video ) memory?

In real mode, there's a 64kb block starting at segment A000 (the first past the 640kb real-mode limit) where you write all your data. To write to different portions of the screen, you have to call a VESA function to do a bank switch.

In protected mode, there are no memory segments and the framebuffer may be linear. You either need to figure out where the extender has relocated the real-mode A000 segment, or find the addres of the linear framebuffer. I can't help you with either of those.

Note that all of that really applies to DOS only.

Quote:

Nah here you are, a tets program. 68 Bytes: Sets VESA mode 1024x768 and draws two lines with a simple putpixel-loop

That is NOT a Windows executable, it's a DOS executable. This will work from a DOS executable. You can't use that code from a native Windows executable - that's what DirectX is for.

gillius
Member #119
April 2000

You could always look at the Allegro source code, which already does this for DOS.

Gillius
Gillius's Programming -- http://gillius.org/

Jacob Dawid
Member #4,045
November 2003
avatar

Ok then, let us assume I would just like to write an engine for MS-DOS. I am using a86 to compile my asm files to obj files. Now I would like to correspond to the methods I have defined before in the asm file. But MinGW complains that it (= the obj file ) has got an unknown file type. Can someone give me a concrete example of how I could manage this task? thx for all replies

Bob
Free Market Evangelist
September 2000
avatar

Quote:

...an engine for MS-DOS....But MinGW complains

Obviously. Mingw is a Windows compiler. Secondly, make sure a86 outputs a compatible object file for GCC. There ought be output switches for that. Thirdly, make sure the code outputted by a86 is compatible with your protected mode compiler (ie: the code is p-mode friendly). Fourthly, why not use the GNU assembler? And finally, Allegro already does this for you, and Allegro is Open Source. So dive in!

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[ -- All my signature links are 404 -- ]

nshade
Member #4,372
February 2004

Jacob:
I think I have figured out where you are getting confused. You don't understand how an x86 CPU operates.

An x86 has two modes. "Real mode" and "Protected mode". Think of "Real mode" as DOS and "Protected mode" as Windows.

These two modes are incompatible with each other. One of the most drastic changes is the memory management and how data is accessed.

In Real Mode, (Or DOS mode), you only have direct access to 640k of ram. (You really have access to 1024K, or 1 MB, but the other 384K is taken by the system) To make matters worse, you really can only access this though 64k segments, even more confusing is that the segemts aren't liniar, and can actually overlap each other. You can point a segment anywere in in the 1MB of addrssable memory and then access data within that segment using a pointer. Most of the memory management is taken care of by the compiler.

Now, at the veeeeery bottom of the memory, there is something called a "vector table". All it is is a list of addresses to jump to when you make an interupt call. There are 256 entries, one for each int call. Then you make an int call, your current place in the program is "bookmarked" on the stack and the int is ran. When the init is done, it will "pop" your last state off of the stack and return to your program.

That's why it's called an "interrupt" it's job is to interrupt your program for a little bit and then allow it to continue.

You can change the addresses in the vector table to point to you own programs. This is called "masking" and creates a kind of psudo-multitasking environment.

Aha! You say. djgpp allows you to allocate all of your memory. Not just 640k.

That's because when you run a program made by djgpp, there is an intrupt vector installed that opens a "window" into the 16 bit address space. This is done with a DOS Protected Mode Interface (Or DPMI)

You can't run a djgpp program without a DPMI manager.
Period.

Windows 9x comes on one, or you can use CWSDPMI.

Now about Protected mode.

When you switch a computer into protected mode, (You can't run both modes at the same time), you gain all kinds of cool benifits.

- You have more registers that hold more data
- You have the ability to keep programs seperated so they don't write all over each other.
- You're memory is no longer segnmented and goes from 0 to however much you have.

Windows runs in protected mode. When you put your fingers into parts of memory that doesn't belong to you, you generate a general protection fault. The program is then teminiated as it can no longer continue.

But here's the problem, and here is the sad thing.

When you go into protected mode, you loose your vector table. It's GONE All those cute things like int 33h for mouse, int 21h for dos functions, and int 10h for graphics are ALL GONE!

The real mode intrrupt system only works with segemnted memory and you gave that up when you switched modes.

When you use a compiler like MingW, you are using a full protected mode compiler that must run it's code NATIVELY in protected mode. It generates windows .EXE files, not dos .EXE files. These two formats are different! It's better to call them by thier real names. a DOS executable, and a Windows PE executable. PE executables are a lot like an ActiveX control. Worlds of diffrence.

So how do you access things without interupts?
You use the Windows API or talk with the hardware directly, but you arn't going to do the later without communicating though a windows driver of some sort. The hardware is protected anyway windows doesn't allow you to directly access it.

All your graphics hardware is ran by a windows driver. Not only that, many graphics cards now a days have low level functions that are SECRET and you MUST access them though a windows driver. Some graphic card companies will even take you to court for violation of trade secrets of you discolse how thier cards work on a low level.

Don't think this is a Windows thing. You can't directly access hardware on Linux either. You have to go through the kernel. The Nvidia driver for Linux is secret. There is no code avilable for it, just the wrapper.

Well, if you are root on linux, you have direct access to hardware, but then no one else can run your program. When using Linux, you also loose your ability to do intrrupts as well.

So how does windows run DOS programs?

It uses a psudo-emulator that catches the calls and tries it's best to handle them. It's not perfect. Windows NT/XP has stricter control over memory management than Win9x and that why it runs less DOS programs.

Pick a mode a stick with it. If you want DOS interrupts, use djgpp. if you want windows protected mode, use MingW, but you can't have both.

Sorry, that's the way the system works.

Do you have any questions?

Oscar Giner
Member #2,207
April 2002
avatar

I may be wrong, since I learned this some time ago, but I think you confused some things in your post (the final result is the same though: that code can't be run if compiled with mingw).

Quote:

- You have more registers that hold more data

You're confusing real vs protected mode with 16 vs 32 bit. the eax/ebx... registers are available under 32bit real mode.

Quote:

When you go into protected mode, you loose your vector table. It's GONE All those cute things like int 33h for mouse, int 21h for dos functions, and int 10h for graphics are ALL GONE!

No. The interrupt table is there and you, in theory, can touch it. It's Windows who doesn't let you touch it. Starting from the 80386, the intel processors have 4 execution levels (if running in protected mode). All user code is executed under level 3, the most restrictive. The interrupt table is not accessible under this execution level.

Quote:

- You have the ability to keep programs seperated so they don't write all over each other.

It's perfectly possible to write a multitasking SO that runs in 16bit real mode (I have done it at university). Programs can mess up the SO, since there's no protection, thought.

Quote:

So how does windows run DOS programs?

It uses a psudo-emulator that catches the calls and tries it's best to handle them. It's not perfect. Windows NT/XP has stricter control over memory management than Win9x and that why it runs less DOS programs.

I'm not very sure about this one, but IIRC you can run real mode programs under a protected mode environment.

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