_bios_disk May Require 3 Tries Before Drive Up to Speed

ID: Q69504

5.10 6.00 6.00a 6.00ax 7.00 | 1.00

MS-DOS                      | WINDOWS

kbprg kbcode

The information in this article applies to:

The C Run-time (CRT), included with:

    - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, and 6.0ax
    - Microsoft C/C++ for MS-DOS, version 7.0
    - Microsoft Visual C++ for Windows, version 1.0

SUMMARY

In Microsoft C versions 5.1, 6.0, 6.0a, 6.0ax, C/C++ version 7.0, and Visual C++ version 1.0, the _bios_disk() routine in the C run-time library uses BIOS interrupt 0x13 to provide several disk-access functions. The ROM BIOS does not automatically wait for the drive to come up to speed before attempting to read the sector, verify the sector, or write to the sector. In the book "IBM ROM BIOS" by Ray Duncan, the recommendation given in each case is to reset the floppy disk system and try the operation three times before assuming an error has occurred.

MORE INFORMATION

The following sample program from the C 6.0 online help makes three attempts to read the disk before giving up. A printf() statement is added to show which read attempt is successful.

Sample Code

/*
 * Compile options needed: none
 */ 

#include <stdio.h>
#include <conio.h>
#include <bios.h>
#include <dos.h>
#include <stdlib.h>

char _far diskbuf[512];

void main( int argc, char *argv[] )

{

   int count;
   unsigned status = 0, i;
   struct diskinfo_t di;
   struct diskfree_t df;
   unsigned char _far *p, linebuf[17];

   if( argc != 5 )
   {
      printf("  SYNTAX: DISK <driveletter> <head> <track> <sector>");
      exit( 1 );
   }

   if( (di.drive = toupper( argv[1][0] ) - 'A' ) > 1 )
   {
      printf( "Must be floppy drive" );
      exit( 1 );
   }

   di.head   = atoi( argv[2] );
   di.track   = atoi( argv[3] );
   di.sector   = atoi( argv[4] );
   di.nsectors = 1;
   di.buffer   = diskbuf;

   // Get information about disk size.

   if( _dos_getdiskfree( di.drive + 1, &df ) )
      exit( 1 );

   // Try reading disk three times before giving up.

   for( count = 1; count <= 3; count++ )
   {
      status = _bios_disk( _DISK_READ, &di ) >> 8;
      if( !status )
         break;
   }

   // Display one sector.

   if( status )
      printf( "Error: 0x%.2x\n", status );
   else
   {
      for(p=diskbuf, i=0; p < (diskbuf+df.bytes_per_sector); p++)
      {
         linebuf[i++] = (*p > 32) ? *p : '.';
         printf( "%.2x ", *p );
         if( i == 16 )
         {
            linebuf[i] = '\0';
            printf( " %16s\n", linebuf );
            i = 0;
         }
      }
   }

   // Which attempt was successful?

   printf( "\nThat was try #%d.\n", count );

   exit( 1 );

}

Additional reference words: kbinf 5.10 6.00 6.00a 6.00ax 7.00 1.00 KBCategory: kbprg kbcode KBSubcategory: CRTIss Keywords : kb16bitonly

Last Reviewed: July 18, 1997