From:	Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: read a specific memory address
Date:	2 May 2001 15:22:27 GMT
Organization:	Aachen University of Technology (RWTH)
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Thomas Schachtner <thomas DOT schachtner AT gmx DOT de> wrote:

> I want to read a value that is stored on (Real-Mode-)Address: F000:0000

That's simple. Use the _farpeekb() function.

> And another value from e. g. 0x03847384 (a 32 bit memory address).

There is no such thing as an absolute memory address, from the point
of view of a DJGPP application. We use a segmented memory model
similar to the 'tiny' model of 16 bit PC programing times, but with
segments potentially 4 Gigabytes long.

You're probably referring to a linear adress space (i.e. the actual
physical address bits at the CPU's pins).  You need special function
of the __dpmi_*() family to map such addresses into the program's
memory space, which are not available in all DPMI environments.

> is the address the same as the value from a pointer?

No.

> Why not?

Because of the Memory Management Unit (MMU) built into all x86 CPUs
since the 386. It translates logical addresses into linear/physical
ones, based upon settings you make in the 'descriptor tables'.

-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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