Mail Archives: djgpp/2000/11/06/21:42:28
On Mon, Nov 06, 2000 at 11:46:42PM +0000, danspam2000 AT my-deja DOT com wrote:
> I am quite new to assembler, but i need to service a hardware interrupt
> very quickly, so have had to code using inline assembler code.
>
> The problem i have is that i can't seem to get a definitive answer
> about how to protect the service routine in memory. I think that i
> should use int 21H, but some books and lists say to use service 48 and
> some say 49, and one said 27! Also, i am not sure exactly what i need
> to pass, and using which registers (some say dx and some say bx), do i
> need to pass a segment or an offset, or both?
Hoh bouy, you've got some confused sources of information. Sounds like they
can't even agree whether to use hex or not. However, the 49 sounds like the
decimal version of the DPMI interrtup (0x31).
As you are in DJGPP, forget just about every source of information out there
and use the definitive guild: the DPMI spec. either
ftp://qdeck.com/pub/memory/dpmispec.zip (wasn't responding when I tried) or
ftp://x2ftp.oulu.fi/pub/msdos/programming/specs/dpmispec.arj (you will have to
use save-as in netscape: I got a screen full of giberish:). There is also
ftp://x2ftp.oulu.fi/pub/msdos/programming/specs/dpmi100.zip which is the DPMI
1.0 spec which is not supported by Windows and only partially supported by
cwsdpmi, but is an excellent source of information (my hardcopy got dog-eared
pretty quickly). Or for the terminally lazy, there's
http://www.delorie.com/djgpp/doc/dpmi/ :) (btw, I got all these from the djgpp
faq).
What you need to do is look up the sections on getting/setting interrupt
vectors and locking/unlocking memory pages. Locking your interrupt memory is
very important because not doing so can cause lots of trouble (and cwsdpmi
will kill your program if you don't (been there, done that:)).
There is plenty of example code out there, but you need to narrow down your
search to djgpp specific code. I believe all the djgpp serial port drivers are
good sources of info (I know bcsio is if you can read asm:).
If you sort out just what you need to know (more specific questions will
help:), you will get more ready answers. Oh, you will probably also file the
sections on real mode callbacks in the dpmi specs helpfull too.
Bill
--
Leave others their otherness. -- Aratak
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