Changing compilation options for BSP building

John Pickwick john.pickwick at
Tue Feb 7 20:41:30 UTC 2006

Thanks for your quick answer Jiri but I intend to try this because I have 
the following problem :
* I've got an application with several tasks and just one floating point 
task, I am targeting the AT697 from ATMEL that has a hardware FPU,
* of course, I created the FP task with FP attribute,
* when RTEMS switches to this task it does not restore the EF bit in PSR 
which implies an "FP disabled" trap on the first floating point instruction,
* looking carefully at this problem under gdb I noticed that there was no 
fp_context pointer field in the thread structure associated with this task 
(this pointer is used to manage the fp_context in threadloadenv.c for 
example). So I assumed that there was something wrong in my bsp compilation.

Therefore I found in thread.h that the fp_context field was enable/disable 
by CPU_HARDWARE_FP define which in turn is conditionned by SPARC_HAS_FPU 
define (in cpu.h) that is set or unset by _SOFT_FLOAT definition (in 
sparc.h). In cpu.h the
CPU_SOFTWARE_FP  is also set to FALSE.

As a consequence :
-msoft-float option
    implies (assumption based on comments in sparc.h)
_SOFT_FLOAT in sparc.h
SPARC_HAS_FPU == 0 in sparc.h
+ CPU_SOFTWARE_FP set to FALSE in cpu.h
    which implies a disabled FP management in threadloadenv.c that is part 
of the bsp.

Can you see what's wrong in my approach ?


----- Original Message ----- 
From: "Jiri Gaisler" <jiri at>
To: "RTEMS Users Mailing List" <rtems-users at>
Sent: Tuesday, February 07, 2006 7:57 PM
Subject: Re: Changing compilation options for BSP building

> I would not recommend to remove the -msoft-float flag from
> CPU_FLAGS. There is not floating point operations done in
> the RTEMS kernel, hence you do not need to generate FPU
> instructions. If you remove the -msoft-float option, newer
> versions of gcc will use FPU registers for certain integer
> operations (!) and the kernel will not run on processors
> without an FPU. Hence, you do not gain anything by removing
> -msoft-float, except the opportunity of crashing on non-FPU
> LEON hardware.
> Jiri.
> John Pickwick wrote:
>> Hi to all,
>> What should I do to change the compilation options used during my bsp
>> buid ?
>> I use the LEON2 / RTEMS 4.6.5 BSP and I'd like to replace the "CPU_FLAGS
>> = -mcpu=cypress -msoft-float" option used during the compilation to
>> suppress the soft-float setting.
>> I tried to set CC_FLAGS_TARGET or CPU_FLAGS directly on my configure
>> command line but it does not work (failed with an 'invalid build alias'
>> error).
>> Thanks for help,
>> John.
>> .

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