Date: Fri, 13 Oct 2000 17:01:35 +0200
From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender: halo1 AT zahav DOT net DOT il
To: Corelli Marco <mcorelli AT gtwparc DOT padova DOT ccr DOT it>
Message-Id: <6480-Fri13Oct2000170135+0300-eliz@is.elta.co.il>
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CC: djgpp AT delorie DOT com
In-reply-to: <39E70A59.1ABE9F69@gtwparc.padova.ccr.it> (message from Corelli
	Marco on Fri, 13 Oct 2000 15:12:57 +0200)
Subject: Re: Accesing from 0xFFFF:F000 to 0xFFFF:FFFF physical memory address
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> From: Corelli Marco <mcorelli AT gtwparc DOT padova DOT ccr DOT it>
> Newsgroups: comp.os.msdos.djgpp
> Date: Fri, 13 Oct 2000 15:12:57 +0200
> 
> Exiting due to signal SIGSEV
> Page fault at eip=00003dba, error=0004

Okay, "Page Fault" means that you are trying to access an address that
is not mapped into your program's address space.  "error=0004" means
you were trying to read from that address (this is consistent with the
use of _farpeekb).  This is explained further in section 12.2 of the
FAQ.

> fs : sel=00c7 base=fffc0000 limit=0003ffff

Didn't you say in your original message that the address you wanted to
map was at FFFC:0000 to FFFF:FFFF?  Are those real-mode segment:offset
addresses, or did you mean to say FFFC0000, a 32-bit physical address?
There's a big difference between these two alternatives.

The above setup of the FS register is correct for 32-bit physical
address FFFC0000, but incorrect for FFFC:0000.

> byte_read = _farpeekb ( selector, i ) ;

Please tell what is the first value of i for which the program
crashes.

>         __dpmi_physical_address_mapping( &mem ) ;
>         selector = __dpmi_allocate_ldt_descriptors ( 1 ) ;
>         __dpmi_set_segment_base_address ( selector, mem.address ) ;
>         __dpmi_set_segment_limit ( selector, mem.size - 1 ) ;

Did all those functions succeed, or did some of them returned -1?