Cedric Herreman wrote:
OK,
I made an extra math module, copying some of the source code from newlib
for the functions i needed. It works.
Another question : if i create an application (in stead of kernel
module) that starts a real time thread. Can i then use math functions
inside the real time running part ?
In the latency example, the sqrt function is used for displaying the
results of the latency test. This is outside the real time task. Is it
possible to use this call in the real time function ? Or any other
library function (that is not performing system calls) ?
Yes. RT threads in user-space have their own FPU context managed by Xenomai.
Cedric.
*/Gilles Chanteperdrix <[EMAIL PROTECTED]>/* wrote:
Cedric Herreman wrote:
> Hello,
>
> I am porting a 2.4 RTAI kernel module to Xenomai 2.0 kernel 2.6.
I used some basic math functions in the original module. This is
posing problems for me now.
>
> In the module source i include . I add -I/usr/include to the
compiler flags and also "-ffast-math -mhard-float".
>
> If i compile this, i get warnings about double definitions of
"__attribute_pure__" and "__attribute_used__".
>
> If i insert the kernel module, i get an error message :
> "Xenomai: Invalid use of FPU in Xenomai context at " + probably
the address of the instruction where the math function is called.
>
> Can anyone give me a hint ? Thanks.
You can only use floating point operations from real-time threads
contexts, not from module initialization and finalization routines, and
you have to signal Xenomai, when creating kernel space real-time
threads, that the thread will be allowed to use FPU. For the RTAI skin,
this is what the rt_task_init function 6th argument is for.
There is currently no math library module in Xenomai. So, the answer is
that you have to avoid math functions, or make a xeno_math module, the
way it is done in RTAI, i.e. using a math library such as the one made
by Sun and used by FreeBSD, or one among the various libcs available.
We once discussed this with Philippe, and a good candidate seemed to be
newlib at that time:
http://sourceware.org/newlib/
Looking at newlib sources, it seems that some of its contents come from
the Sun library too.
--
Gilles Chanteperdrix.
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Philippe.
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