Message-ID:	<3B8659BB.C6CE272@student.uni-ulm.de>
Date:	Fri, 24 Aug 2001 15:42:19 +0200
From:	Karsten Schmidt <Karsten.Schmidt*no_spam*@student.uni-ulm.de>
Organization:	=?iso-8859-1?Q?Universit=E4t?= Ulm
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Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Thoughts on physical address and DMA
References:	<f5c79439 DOT 0108171412 DOT 689b2a6b AT posting DOT google DOT com> <3b8141a5 DOT sandmann AT clio DOT rice DOT edu>
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi!

More than one year ago I had almost the same problem:
I was trying to access a digital IO-card using Bus-Master DMA.

The following function virtToPhys is based on the source code 
from N. Jarvis and has been adopted to run with PMODE/DJ.

The resulting program will only run under protection level 0 
(e.g. CWSDPR0 or PMODE/DJ). 


/****************************************************************************/
/*                              University of
Ulm                           */
/*--------------------------------------------------------------------------*/
/*   Microelectronics
Department                                            */
/*   Physical address
mapping                                               */
/*  
phys_adr.c                                                            
*/
/*   K. Schmidt                                                   
(Author) */
/*   07.12.2000                                              (last
changed) */
/*   1.1                                              (last tested
version) */
/*--------------------------------------------------------------------------*/
/*   Special
features:                                                      */
/*     - Based on the sourcecode of  N. Jarvis from the DJGPP Mail
Archiv   */
/*      
djgpp/1996/09/18/05:03:32                                          */
/*     - Calculation of the physical adress for an given linear
address     */
/*     - Requires protection level 0 (z.B. CWSDPR0.EXE,
PMODEDJ.EXE)        */
/*     - Compile with -D PMODE to use with
PMODEDJ.EXE                      */
/*--------------------------------------------------------------------------*/
/*  
Changes:                                                              
*/
/*                                                                         
*/
/* Date        Ver  Author  where ?             
what?                      */
/* 13.03.2000  1.0   KS     Initial
release                                 */
/* 07.12.2000  1.1   KS     Startup flags         
_CRT0_FLAG_UNIX_SBRK     */
/*                          virtToPhys()           Changed for
PMODE/DJ     */
/****************************************************************************/

/* Just to make me feel happier, I use the following. May not be needed.
*/
int _crt0_startup_flags = (_CRT0_FLAG_FILL_SBRK_MEMORY |
                           _CRT0_FLAG_FILL_DEADBEEF    |
                           _CRT0_FLAG_NONMOVE_SBRK     |
                           _CRT0_FLAG_LOCK_MEMORY      
#ifdef PMODE                           
                           /* Additional flag for PMODE/DJ*/
                           | _CRT0_FLAG_UNIX_SBRK
#endif
                           );

static __inline__ unsigned long _my_cr3(void)
{
   unsigned long result;
   __asm__("mov %%cr3,%0" : "=r" (result));
   return result;
}

/* Convert virtual to physical address */
unsigned long virtToPhys(void *virtualPtr)
{
   unsigned long DSLinearAddr;

   if (__dpmi_get_segment_base_address(_go32_my_ds(), &DSLinearAddr) !=
-1)
   {
      unsigned long pde, pdeAddr, pte, pteAddr, linear;

      /* Calculate linear address */
      linear = (unsigned long) virtualPtr + DSLinearAddr;

      /* Changed for PMODE/DJ 1.3:
         Physical Address == Linear Address! */
         
#ifdef PMODE         
      return (linear);    
#endif

      /* Calculate Page Directory Entry address */
      pdeAddr = _my_cr3() + ((linear & 0xffc00000L) >> 20);

      /* Read Page Directory Entry */
      pde = _farpeekl(_dos_ds, pdeAddr);

      /* Calculate Page Table Entry address */
      pteAddr = (pde & 0xfffff000L) + ((linear & 0x003ff000L) >> 10);

      /* Read Page Table Entry */
      pte = _farpeekl(_dos_ds, pteAddr);

      /* Calculate and return Page Frame address */
      return (pte & 0xfffff000L) + (linear & 0x00000fffL);
   }
   else
      return 0L;
}

- Raw text -