int86() C command

[PavelChekov]

Can I use the following to print to my printer on an Intel64 system?:

Code: Select all

void printchar(char c){

  union REGS regs;

  regs.h.ah=0x00; //print character function
  regs.h.al=c; //character to print
  regs.x.dx=0x00; //print port to print to (LPT1)
  int86(0x17,&regs,&regs); //interrupt

}

[nexos]

No, int86 was used on old DOS systems for C code to access the BIOS. Nowadays, the world has moved on from real mode and the BIOS.

[kzinti]

Well you can if you implement int86()

[nullplan]

Well you can if you implement int86()

And have a BIOS interface (or CSM in UEFI mode).

[neon]

Hi,

If interested, int86 was the original inspiration for this function in our boot loader here. Its been a while since I wrote this type of code but IIRC it would look something like:

Code: Select all

void printchar(char c){
  REGS regs;
  _ah (regs.eax) = 0x00;
  _al (regs.eax) = c;
  _dx (regs.edx) = 0x00;
  io_services (0x17,&regs,&regs);
}

[Thomas]

Hi Pavel,
That looks like legacy code and makes only sense when using real mode. ( int86 is part of the old dos turbo C++ library if I remember correctly). While you would be able to get it to work in a i64 using some sort of emulation layer ( dos box , boxed wine etc ). It is not recommended. All modern operating system provide an API for printing ( I/O ) in general. It would simply be best to use them instead.

--Thomas

[bzt]

Can I use the following to print to my printer on an Intel64 system?

Under special circumstances, yes. But even when you could, I wouldn't recommend it, as it would be extremely slow, plus you probably won't have Teletype video mode anyway, only pixel-based graphics on modern machines (only a few BIOS implements that and only for some video modes. Chances are that that BIOS int won't work). Check out PC Screen Font or consider using a minimalistic library such as Scalable Screen Font instead.

For printing not on screen but to somewhere else, you should use IO ports. It's not that difficult, parallel port is very easy to program in particular. However again, chances are good that your modern Intel64 machine doesn't have an LPT port in the first place...

That looks like legacy code and makes only sense when using real mode.

Not really, you could switch modes temporarily.

int86 is part of the old dos turbo C++ library if I remember correctly

Also in Minix (see source line 8861). It switches to real mode, does the BIOS call and then switches back to protmode. The caller of int86() is none the wiser. You could implement something like that in long mode too, but BIOS must exists in the first place of course (and the machine must have an LPT peripheral which is unlikely these days).

Cheers,
bzt

[PavelChekov]

Hi Pavel,
int86 is part of the old dos turbo C++ library if I remember correctly

I like looking through old C programming books, and trying to follow the tutorials today.