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Date: Wed, 6 Feb 2002 10:01:29 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: hskim <hskim AT future DOT co DOT kr>
cc: djgpp AT delorie DOT com
Subject: Re: PCI Memory mapping?
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On Wed, 6 Feb 2002, hskim wrote:

>                 meminfo.handle = 0xf5800000;
>                 meminfo.size = 0x200000;
>                 meminfo.address = 0;
> 
>                 nRet = __dpmi_physical_address_mapping(&meminfo);
> 
>                 printf("Result = %d, %08x,%08x,%08x\n",
>                                nRet,
>                                meminfo.handle,
>                                meminfo.size,
>                                meminfo.address);
>                 if (nRet)
>                    return;
> 
>                 p = meminfo.address;
> 
>                 p[0] = 0;  // program is crashed!

That's because you didn't allocate a selector for accessing this
memory, and didn't set up that selecor's segment to span the range of
addresses you want to access.  __dpmi_physical_address_mapping only
creates a mapping between physical addresses and logical addresses,
but doesn't provide a selector to access the mapped memory.

See section 18.7 of the DJGPP FAQ list, it shows a skeleton of code
that does all of the above.