BUG: Debugging With Mono And VGA Can Cause Screen Corruption

• Microsoft Codeview for MS-DOS, versions 4.0, 4.01, and 4.1

SYMPTOMS

When using the MS-DOS "mode mono" command to debug a graphics application on a secondary monochrome monitor (VGA being the primary monitor), screen corruption can result on both monitors.

RESOLUTION

To work around the problem, do not use the mode mono command. Instead, either debug on the primary VGA monitor or use the /2 command line option to display Codeview's windows on the monochrome monitor (instead of on the VGA monitor).

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The sample program below demonstrates the problem. Build a debug version and enter the following commands at the DOS prompt:

msherc mode mono cv /b /s modes

Once you have started Codeview, enter the following commands in the command window:

bp .49 g g

At this point both the VGA monitor and the monochrome monitor may display corrupt information.

Sample Code

/* Compiler Options Needed:  /AL /Zi /Od
*/

#include <conio.h>
#include <stdio.h>
#include <graph.h>

short modes[] = { _TEXTBW40,     _TEXTC40,      _TEXTBW80,
                  _TEXTC80,      _MRES4COLOR,   _MRESNOCOLOR,
                  _HRESBW,       _TEXTMONO,     _HERCMONO,
                  _MRES16COLOR,  _HRES16COLOR,  _ERESNOCOLOR,
                  _ERESCOLOR,    _VRES2COLOR,   _VRES16COLOR,
                  _MRES256COLOR, _ORESCOLOR
                };
char *names[] = { "TEXTBW40",    "TEXTC40",     "TEXTBW80",
                  "TEXTC80",     "MRES4COLOR",  "MRESNOCOLOR",
                  "HRESBW",      "TEXTMONO",    "HERCMONO",
                  "MRES16COLOR", "HRES16COLOR", "ERESNOCOLOR",
                  "ERESCOLOR",   "VRES2COLOR",  "VRES16COLOR",
                  "MRES256COLOR","ORESCOLOR"
                };

void main(void)

 short c, i, j, x, y, row, num = sizeof(modes) / sizeof(modes[0]);
 struct _videoconfig vc;
 char b[500];              /* Buffer for string */

 _displaycursor( _GCURSOROFF );

 /* Try each mode. */
 for( i = 0; i <= num; i++ )
 {
  for (j = 0; j < 5; j++ )
  {
   /* Try each possible number of rows. */
   row = _setvideomoderows( modes[i], rows[j] );
   if( (!row) || (rows[j] != row) )
    continue;
   else
   {
    _getvideoconfig( &vc );
    y = (vc.numtextrows - 12) / 2;
    x = (vc.numtextcols - 25) / 2;

    /* Use text window to place output in middle of screen. */
    _settextwindow( y, x, vc.numtextrows - y, vc.numtextcols - x );

    /* Write all information to a string, then output string */
    c  = sprintf( b,     "Video mode: %s\n", names[i] );
    c += sprintf( b + c, "X pixels:   %d\n", vc.numxpixels );
    c += sprintf( b + c, "Y pixels:   %d\n", vc.numypixels );
    c += sprintf( b + c, "Columns:    %d\n", vc.numtextcols );
    c += sprintf( b + c, "Rows:       %d\n", vc.numtextrows );
    c += sprintf( b + c, "Colors:     %d\n", vc.numcolors );
    c += sprintf( b + c, "Bits/pixel: %d\n", vc.bitsperpixel );
    c += sprintf( b + c, "Pages:      %d\n", vc.numvideopages );
    c += sprintf( b + c, "Mode:       %d\n", vc.mode );
    c += sprintf( b + c, "Adapter:    %d\n", vc.adapter );
    c += sprintf( b + c, "Monitor:    %d\n", vc.monitor );
    c += sprintf( b + c, "Memory:     %d",   vc.memory );
    _outtext( b );
    _getch();
   }
  }
 }
 _displaycursor( _GCURSORON );
 _setvideomode( _DEFAULTMODE );