From:	johne AT parallax DOT co DOT uk (John Eccleston)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Displaying the VESA OEM string
Date:	Mon, 06 Jan 97 09:25:44 GMT
Organization:	Parallax Solutions Ltd
Lines:	105
Message-ID:	<5aqgd9$h4i@red.parallax.co.uk>
NNTP-Posting-Host:	parsnip.parallax.co.uk
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi All,

First let me apologise if what I am asking is in the FAQ, I
have looked (honest) but either I am blind or stupid!

I am trying to display the OEM string for the VESA graphics card
in my system.  However this always causes the program to
access violate.  Could someone please point me in the right
direction.  By looking at the FAQ I think I need to use the
_farpeekb (etc) functions but how do I convert the pointer given
in the VESA info structure to the required (segment*16 + offset)
value.

The program is given below and it gives the following error

Exiting due to signal SIGSEGV
General Protection Fault at eip=0000535e

Thanks in advance

John

------> Cut here <-----------
#include <stdio.h>
#include <dpmi.h>
#include <go32.h>
#include <assert.h>
#include <string.h>

#define PACKED __attribute__ ((packed))

#pragma pack(1)
/*
 * The following structure is used to retrieve information
 * about the VESA capabilities of a systems graphics card
 */
typedef struct VBEInfo
{
   char  VESASignature[4] PACKED; /* 'VESA' 4 byte signature      */
   short VESAVersion      PACKED; /* VBE version number           */
   char  *OEMStringPtr    PACKED; /* Pointer to OEM string        */
   long  Capabilities     PACKED; /* Capabilities of video card   */
   short *VideoModePtr    PACKED; /* Pointer to supported modes   */
   short TotalMemory      PACKED; /* Number of 64kb memory blocks */
   char  reserved[236]    PACKED; /* Pad to 256 byte block size   */
} VBEInfo;

#define VBE_MajorVersion(x) (((x) >> 8) & 0xFF)
#define VBE_MinorVersion(x) ((x) & 0xFF)

#pragma pack()

int VBE_detect(VBEInfo *vbeinfo)
{
   __dpmi_regs
      regs;
  
   regs.x.ax = 0x4F00;
   regs.x.di = __tb & 0x0F;
   regs.x.es = (__tb >> 4) & 0xFFFF;

   memset(vbeinfo, 0, sizeof(VBEInfo));
   __dpmi_int(0x10, &regs);
   dosmemget(__tb, sizeof(VBEInfo), vbeinfo);

   if (strncmp(vbeinfo->VESASignature, "VESA", 4) != 0)
   { 
      return 0;
   }
   else
   {
      return vbeinfo->VESAVersion;
   }
}

main()
{
   VBEInfo vesaInfo;
   
   if (VBE_detect(&vesaInfo))  
   {
      printf("VESA compliant video card found\n");
      printf("\tVersion : %d.%d\n",
             VBE_MajorVersion(vesaInfo.VESAVersion),
             VBE_MinorVersion(vesaInfo.VESAVersion));
      printf("\tVideo memory : %d K Bytes\n", vesaInfo.TotalMemory * 64);
      printf("Manufacturer : %s\n", vesaInfo.OEMStringPtr);
   }
   else
   {
      printf("No VESA support!\n");
   }
}
------> Cut here <-----------

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