Date: Mon, 13 Jun 94 17:32:47 EDT
From: hvb AT netrix DOT com
To: dj AT ctron DOT com (DJ Delorie)
Cc: DJGPP AT sun DOT soe DOT clarkson DOT edu
Subject: Access to the 1MB memory in protected mode
Reply-To: hvb AT netrix DOT com

DJ Delorie writes:
 > 
 > In non-DPMI mode, you can try adding 0xe0000000 to the physical
 > address and go32 may map it for you.
                    ^^^
                    |||
Dear DJ,

This is in refer to your reply on the subject a while ago.  What do
you mean by the word 'may' above?  How do I force go32 to set up the
mapping?

I have a memory mapped hardware device which is mapped to the
0xd0000-0xd3fff address range.  In the program I included below, it
does not seem to access the real physical address unless I have a
debug32 breakpoint set up.  Once the debug32 breakpoint is entered I
am able to access the memory location.  I have tried to make a bdos
call to force a protected-to-real switching but it did not seem to
work either.

--------------  Program example -----------------
void
main
(
int   argc,     /* number of command line arguments */
char *argv[]    /* array of pointers to command line arguments */
)
{
  unsigned short *rom_init = (unsigned short *)0xd0000412;

  bdos (0x0b, 0, 0);           /* Try to force a protected-to-real
                                  switch */

  outpb (0x240, 0x40);         /* This code sets up the board mapping/
  outpb (0x240, 0);            /* to 0xd0000 */
  outpb (0x242, 0xd000 >> 9);

  outpb (0x240, 0x20);

  *rom_init = 0;               /* This does not happen unless a breakpoint
                                  is entered prior to this point. */
}

---------------- End of example ----------------------

Thanks,
==============================================================
Hung Bui                           Internet: hvb AT netrix DOT com
Netrix Corporation                    Phone: +1 703 793 1016
13595 Dulles Technology Drive           Fax: +1 703 713 3805
Herndon Va 22071
==============================================================