Message-ID: <01BB512C.115C67A0@psp3>
From: Steve Higgins <steve AT psp-digital DOT co DOT uk>
To: "'DJGPP Mail List'" <djgpp AT delorie DOT com>
Subject: Replacing stdin / stdout with my own versions.
Date: Mon, 3 Jun 1996 09:07:01 -0000
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Hi all,

I have a rather complex command line oriented program (similar to gdb) 
which uses stdin and stdout to get and show information.

What I want to do is to write my own wrapper program which grabs 
stdin and stdout and presents a nicer user interface to the world, but talk
to the low level app through these grabbed input and output.

I started by writing a simple program to see if this is possible (see below).
What it should do is grab the keyboard BIOS interrupt (0x16) and reply
with a carrage return whenever a keypress is asked for.

What seems to happen is that the program gets as far as getchar() and then
waits for ever.

I have also tried replacing the stdinInterrupt with

void stdinInterrupt(_go32_dpmi_registers *r)
{
    r->x.ip  = OldStdinVector.rm_offset;
    r->x.cs = OldStdinVector.rm_segment;
    _go32_dpmi_simulate_fcall_iret(r);
}

With the same hanging problem.

Does anyone have any idea what I am doing wrong?
Has anyone done anything similar in the past - any source code?

Thanks for any help

Steve.

/************ start of source code **************/

#include <conio.h>
#include <stdio.h>
#include <go32.h>
#include <dpmi.h>
#include <string.h>


static _go32_dpmi_seginfo   NewStdinVector;
static _go32_dpmi_seginfo   OldStdinVector;
static _go32_dpmi_registers StdinRegs;

int count = 0;

void stdinInterrupt(_go32_dpmi_registers *r)
{
  switch(r->h.ah)
    {
    case 0:           /* get char (blocking) */
      r->h.ah = 0x1C;    /* scan code */
      r->h.al = 0x0D;   /* ascii code */
      r->x.flags = 0; /* ZF = 0 means char ready (probably not needed) */
      break;

    case 1:           /* report whether character ready */
      r->x.flags = 0; /* ZF = 0 means char ready        */
      break;
	
    case 2:           /* get shift status */
      r->h.al = 0;    /* holds shift state */
      break;
    } 
}

#define INTVECTOR 0x16

void stdinInit()
{
  /* Get the bios keyboard services interrupt vector. */
    
  _go32_dpmi_get_real_mode_interrupt_vector(INTVECTOR,&OldStdinVector);
  NewStdinVector.pm_offset = (int) stdinInterrupt;
  _go32_dpmi_allocate_real_mode_callback_iret(&NewStdinVector,&StdinRegs);
  _go32_dpmi_set_real_mode_interrupt_vector(INTVECTOR,&NewStdinVector);
  
}

void stdinExit()
{
  _go32_dpmi_set_real_mode_interrupt_vector(INTVECTOR,&OldStdinVector);
  _go32_dpmi_free_real_mode_callback(&NewStdinVector);
}

int main()
{
  int ch;
  stdinInit();

  ch = getchar();
  putchar(ch);
  
  stdinExit();

  return 0;
}