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From: grog@lemis.uucp (Greg Lehey)
Newsgroups: comp.os.386bsd.development
Subject: Re: Gnu Inline Assembly question
Message-ID: <3105@adagio.lemis.uucp>
Date: 2 Apr 94 07:56:05 GMT
References: <2n76gvINNbjn@uwm.edu>
Organization: LEMIS, W-6324 Feldatal, Germany
Lines: 43
In article <2n76gvINNbjn@uwm.edu> knier@miller.cs.uwm.edu (Robert Knier ) writes:
>
> Sorry if this doesn't belong here - but since this is for
> developing a Future Domain, Seagate ST01/02 device driver here goes.
> Does any one have info on inline assembly with the gnu compiler? More
> specifically, I am trying to write some assembly code to speed up data
> transfer to and from a future domain card. I am wondering on the
> syntax of inline assembly code.
Read the gcc documentation. It is not as simple as it might appear: in
particular, you need to supply parameters and type information. I have
found it easier to do this by defining an inline function which
actually does the work, e.g.:
static INLINE void
outb (short port, char val)
{
__asm__ volatile ("out%B0 %0,%1"::"a" (val), "d" (port));
}
static INLINE unsigned char
inb (short port)
{
unsigned int ret;
__asm__ volatile ("in%B0 %1,%0":"=a" (ret):"d" (port));
return ret;
}
From memory, the __asm__ command is split into 3 parts, separated by
colons (logical, isn't it?). The first is the code itself, the second
is an input parameter list, the third is a return parameter list. The
parameters are referred to by position (%0, %1, etc.) in the code. The
"=a" and "d" in the example above are information on what kind of
parameter may be supplied - this is discussed in some depth in the gcc
manual, and I find I always have to go back to check up, so I won't go
into more detail here (and risk making mistakes :-).
--
---------------------------------------------
Greg Lehey | Tel: +49-6637-1488
LEMIS, Schellnhausen 2, | Fax: +49-6637-1489
36325 Feldatal, Germany | Mail: grog@lemis.de