sparc-rtems4.7-gcc versus fpu

Stephan Gruenfelder stephan.gruenfelder at space.at
Wed Jun 13 08:38:10 UTC 2007


Peter,

I agree with Joel that this is not an RTEMS topic. The answer most likely is the 
-mv8 option of gcc, which enables the FPU. However, if you compile mission 
critical code for the AT697E (AT697E-2E-E), then you might want to turn off the 
FPU anyway, because of a Multiplier/Divider failure in the LEON2 VHDL model (see 
errata sheet of the AT697).

Regards
Stephan

Joel Sherrill wrote:
> Peter A. Krauss wrote:
>> Hello,
>>
>> I have downloaded sparc-rtems4.7 and would like to use it for a leon2 
>> target with fpu. I am puzzled on how the compiler inserts fpu 
>> instructions. My summary is:
>>
>> - The compiler does insert fpu instructions, if no fpu command line 
>> option is given or if "-mhard-quad-float" is used.
>>
>> - The compiler does not insert fpu instructions, if "-mfpu" or 
>> "-mhard-float" is used.
>>
>> Why?
> It would take a gcc expert to answer for sure but I recall a recent
> discussion on the gcc list which sounds like it is happening here.
> I suspect that since hard FPU is the default, -mfpu is toggling the
> default and turning it into soft float.
> 
> I tried this with gcc 4.2.0 and got your behavior.  I tried it with
> the RTEMS 4.6 gcc 3.2.3 and it still generated hardware FPU instructions.
> 
> Can you send this report to gcc AT gcc.gnu.org and CC me?  I think
> someone over there will have a better answer.
> 
> --joel

-- 

==============================================
   Stephan GRÜNFELDER
   Dr. techn.
   Software Engineer

   AUSTRIAN AEROSPACE Ges.m.b.H.
   Stachegasse 16
   A-1120 Vienna, AUSTRIA / EUROPE
   Internet: http://www.space.at

   Tel.   : +43-1-80199/5530
   Fax    : +43-1-80199/5577
   E-Mail: stephan.gruenfelder at space.at
==============================================
   This email is for information only!
==============================================



More information about the users mailing list