Soft Float for PC386

Joel Sherrill joel.sherrill at
Tue Jan 23 20:16:17 UTC 2001

angelo wrote:
> I have successfully run  RTEMS apps on a Pentium using the pc386 build,
> however, when I attempt to run the apps (including the hello world ) on a
> 386 with no co-processor, The console just display an infinite Exception
> which I cannot read.

Hmmm.. I would be surprised if the lack of an FPU is causing this.  But
stranger things have happened over the years.  What RTEMS version are
you trying?  It might also be worth it to put a "while 1" loop in the
exception handler temporarily so the message won't disappear.

> I suspect that it may be that soft float is required,
> but I am not sure.  Is there a way of ensuring that I am not trying to use
> the co-processor and am in fact using the soft floating point libraries.

The answer is simple and not so simple at the same time.  The standard
gcc sources do not have soft-float support turned on for the i386 targets.
The RTEMS gcc patches and RPMs post 4.5.0 do include support for this. 

If you look at the ts_386ex target in recent snapshots, its CPU_CFLAGS
should be the basis for adding a new pc386 variant (like pc[56]86 and
pck6).  Right now all pc386 variants assume an FPU.

> --
> Angelo Fraietta
> PO Box 859
> Hamilton NSW 2303
> Home Page
> There are those who seek knowledge for the sake of knowledge - that is
> There are those who seek knowledge to be known by others - that is VANITY
> There are those who seek knowledge in order to serve - that is LOVE
>     Bernard of Clairvaux (1090 - 1153)

Joel Sherrill, Ph.D.             Director of Research & Development
joel at                 On-Line Applications Research
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