Date:	Tue, 23 Jul 1996 08:22:24 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	Luke Steele <luke AT jaglogic DOT demon DOT co DOT uk>
Cc:	djgpp AT delorie DOT com
Subject:	Re: Inline assembly and DMA transfers.
In-Reply-To:	<DuyHz5.DtH@ftp.jags.co.uk>
Message-Id:	<Pine.SUN.3.91.960723081342.9913B-100000@is>
Mime-Version:	1.0

On Mon, 22 Jul 1996, Luke Steele wrote:

> 	I'm planning to write some code that will require inline assembly.
> However, I have been unable to work out how to do this - specifically,
> how do I indicate to the compiler that the code is assembly, in the
> way that the 'asm' statement does in Borland C?  I've read the FAQ in
> some detail, and the online documentation as well, but these only
> illustrate the syntax of the assembly, and not how to place it inline
> with the C code.

This is all explained in the GCC on-line docs.  Download and install the 
Texinfo package (v2gnu/txi360b.zip from the same place you get DJGPP) and 
then type the following words of wisdom from the DOS prompt:

	info gcc "C Extensions" "Extended Asm"

(note the quotes and the letter-case: they are important).  You should 
now be able to read the chapter on the GCC inline assembly facilities.

> 	Also, I'm planning to do a DMA transfer.  I've performed DMA transfers
> in real mode before with no problem, but are there any special
> considerations when making a transfer in protected mode?

The main consideration is that in protected mode memory is mapped, so the 
address of a buffer is usually NOT its physical address.  Since DMA 
controller needs to know the physical address, you will have to use DPMI 
calls that return physical address given a logical one.

Another possibility is to use the VDS (Virtual DMA Services) API, but not 
every memory manager/DPMI host supports them (CWSDPMI doesn't, so VDS
won't work when CWSDPMI is running without a memory manager).

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