David,
On Mon, Apr 10, 2000 at 05:02:25PM -0400, David J. Christini wrote:
> I've seen a couple of posts on this list regarding strange floating point
> related crashes. I'm having such a problem, and I can't seem to solve it.
>
> I believe it involves the fact that my floating point variables are in
> shared memory (using mbuff with volatile ... however I had the same
> crashing problems last week before I switched over to mbuff from the old
> shared memory approach). I #include <float.h> and pthread_setfp_np. I use
> the following shared memory struct:
>
> typedef struct {
> unsigned char head;
> int scan_index; //index holding current analog input scan
> int current_fp; //current value of fp
> int current_xx; //current value of state variable
> //float g; //g feedback proportionality control parameter
> int g; //g feedback proportionality control parameter
> unsigned int ai_chan[NUM_AD_CHANNELS_TO_USE];
> unsigned char tail;
> } SharedMemStruct;
>
> When I compile and run my application with only int's (as it currently
> reads), it doesn't crash. However if I change g to float, my application
> crashes my computer occasionally, but not always. The application has
> three floating point operations involving g.
>
> Is there anything I should be doing to avoid this? My application, which
> is a feedback control process, needs to use float for g, so I don't really
> know how to get around this ... the one thing I'm considering is trying
> RTAI ... any thoughts?
>
I use kernel 2.2.13, RTL 2.0. My RT application uses double variables
and operations heavily including sin(), cos(), sqrt(), atan2(). I also
use shared memory (Tomek Motylewski's mbuff). I don't remember any
crash caused by floating point operations. I'd expect your trouble is
caused by something else (float/double confusion?, kernel/user memory
context trouble?).
Regards,
--
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Pavel Andris | tel: +421 7 5941 2167
Institute of Control Theory and Robotics | fax: +421 7 5477 6045
Slovak Academy of Sciences |
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SK - 842 37 Bratislava |
Slovakia |
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