gxx problem

[jakelstr]

When i compile my code with gxx(C:\djgpp\bin\gxx -c C:\os\kernel.cpp -ffreestanding -nostdlib -fno-builtin -fno-rtti -fno-exceptions -o C:\os\kernel.o) it compiles without a flaw, but, then it doesn't give output

[Daedalus]

You'll have to give us your sourcecode for us to be able to determine why.

[jakelstr]

it's all from a tutorial but,

Code: Select all

//Video.h
#ifndef VIDEO_H
#define VIDEO_H //so we don't get multiple definitions of Video

class Video
{
public:
Video() ;
~Video() ;
void clear() ;
void write(char *cp) ;
void put(char c) ;
private:
unsigned short *videomem ; //pointer to video memory
unsigned int off ; //offset, used like a y cord
unsigned int pos ; //position, used like x cord

}; //don't forget the semicolon!
#endif

Code: Select all

//Video.cpp
#include "Video.h"
Video::Video()
{
pos=0 ; off=0 ;
videomem = (unsigned short*) 0xb8000 ;
}

Video::~Video() {}

void Video::clear()
{
unsigned int i;

for(i=0; i<(80*25); i++)
{
videomem[i] = (unsigned char) ' ' | 0x0700 ;
}
pos=0 ; off=0 ;
}

void Video::write(char *cp)
{
char *str = cp, *ch;

for (ch = str; *ch; ch++)
{
put(*ch) ;
}
}

void Video::put(char c)
{
if(pos>=80)
{
pos=0 ;
off += 80 ;
}

if(off>=(80*25))
{
clear() ; //should scroll the screen, but for now, just clear
}

videomem[off + pos] = (unsigned char) c | 0x0700 ;
pos++ ;
}

Code: Select all

//Kernel.cpp
#include "Video.h"

int main(void)
{
Video vid ; //local, (global variables need some Run-Time support code)

vid.write("Hello, world!") ;
}

[carbonBased]

How are you running this? Linking to an .exe and running?

You're assuming video memory is at 0xb8000. I don't believe this is the case when you use DJGPP in conjunction with CWSDPMI (the default DPMI "agent"). You will have to use some of the DJGPP specific functions in order to get a far pointer to video memory.

For example, you could create your own selector:
short video_selector;

video_selector = __dpmi_allocate_ldt_descriptors(1);
__dpmi_set_segment_base_address( video_selector, linear_address);
__dpmi_set_segment_limit( video_selector, 2000000L); /* 2 Megs */

And then write to video memory using:
_farpokeb(video_selector, offset, value);

The other method is to "enable near pointers" and reference the base of conventional memory:
__djgpp_nearptr_enable();
char *video = (char *)0xb8000;
video[offset + __djgpp_conventional_base] = value;
__djgpp_nearptr_disable();

--Jeff

[jakelstr]

I am compiling to .O files. But when i go to "C:\os" which is where i tell it to complie, there is no .O file.

[carbonBased]

I see... this is what I thought you meant, then I second guessing my interpretation of "output"

Do you get an object file when you try to compile without the specified compile options? ie: a strict gcc -c file.cpp -o file.o?

If you put in an explicit #error clause, does the compiler report a proper failure code?

Lastly, what platform are you using? djgpp was originally meant to run in Dos. From what I've heard, it's not overly well suited for windows operation... and, personally, I prefer the overall cygwin environment. You might want to check that out.

Cheers,
Jeff

[jakelstr]

I'm getting ready to download a vmware linux to try it on. Post my results later.