🚀 go-pugleaf

ewirtz@bga.com (Erik Wirtz) wrote:

>I am trying to convert a program that accesses a network card
>to 32bit Protected mode.  It consists of a small C program and a 
>small ASM program,  It works flawlessly in real mode.  When compiled
>under 32bit Protected Mode it generates GP's.  I need help getting

My guess is you are trying to access memory using a real mode 
segment/offset pair.  You can not do this from protected mode.
You must allocate a selector and set its base address and limit.

In Windows 16 bit or Borland 16 bit DPMI you can use 
AllocSelector(), SetSelectorBase() and SetSelectorLimit().
but since your are using Borland 32 bit DPMI these are not
available, therefore, you must call DPMI yourself.  If you
do this, though, your program will not run in a DOS shell
under Windows 95 (it will if you use 16 bit DPMI).  Here is
some code that will allocate a selector and set its base/limit:

/**************************************************************************
*
* Allocates a selector with base addres 'dwBaseAddress' and limit of
* 'dwLimit'.  The return value is the new selector if the function is 
* successful or 0 on failure.
* 
* This is function should not be confused with the Windows API
function
* of the same name which simply allocates a selector.
*
 ********************************************/
SELECTOR _EXPORT AllocSelector(DWORD dwBaseAddress, DWORD dwLimit)
{
  SELECTOR selNew;

  asm {
    // dwLimit must be non-zero
    mov   eax, dwLimit
    or    eax, eax
    jz    short Fail
  
    // Allocate a data selector (DPMI sets default acces rights)
    mov   ax, 0x0000
    mov   cx, 0x0001
    int   DPMI_INT
    jc    short Fail
    mov   selNew, ax

    // Set the selector's base address
    mov   ax, 0x0007
    mov   bx, selNew
    mov   ecx, dwBaseAddress
    mov   dx, cx
    shr   ecx, 16
    int   DPMI_INT
    jc    short Fail

    // Set the selector's limit
    mov   ax, 0x0008
    mov   bx, selNew
    mov   ecx, dwLimit
    dec   ecx
    mov   dx, cx
    shr   ecx, 16
    int   DPMI_INT
    jc    short Fail
  }
Success:
  return selNew;
Fail:
  return 0;
} 

------------------------------------------------------------
Donald K. Forbes                     e-mail:  don@mythos.com
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