I did some tests and now I'm completely confused. I removed almost all
code from my usart ISR, ISR code just retrive only a byte from RCREG
register and return. So it doesn't call any other routines.
My main() routine looks like this:
volatile long d1,d2;
float tmp,dist;
unsigned int dst;
int main(){
// some intilaization code of important regs
[...]
stdout = STREAM_USART;
while (1){
d1=d2=100;
d1=d1*d1;
d2=d2*d2;
if(d1 !=10000 || d2!=10000) printf("d1=%lu d2=%lu\r\n",d1,d2);
tmp=(float) (d1+d2);
dist=sqrtf(tmp);
dst=(unsigned int) dist;
dst=dst*2;
if( dst != 282){
printf("dst=%u dist=%.4f \r\n",dst,dist);
}
}
when isart int is active (usart receive data), main loops return
randomly wrong values:
dst=259 dist=141.4214
d1=10000 d2=9984
dst=0 dist=0.0000
dst=2 dist=1.0000
dst=257 dist=141.4214
dst=2 dist=1.0000
d1=9984 d2=10000
dst=257 dist=141.4214
dst=2 dist=1.0000
dst=2 dist=1.0000
dst=0 dist=141.4214
dst=0 dist=0.0000
d1=9984 d2=10000
d1=10000 d2=9984
So, when interrupt is enabled all int, long or float calculations are
randomly wrong.
I know, these calcuations are not atomic, but why they are wrong even when all
int/long sdcclib functions (mulint etc) are compiled as reentrant
(and even not in use in ISR)?
When I disable interrupt calculations problem just disappear.
regards,
ml
2012/6/11, M L <maricol...@gmail.com>:
> Hello,
> I discover some strange behaviour of sqrtf() function when usart
> interrupts are enabled.
> My sdcclibs are compiled with --stack-auto option, libm too.
> My program is simple and just do a sqrt calculations in endless loop
> (my code compiled is with --stack-auto):
>
> float val;
> unsigned int x;
> while(1){
> val=sqrtf(20000);
> x=(unsigned int) val;
> if(x!=141) printf("x=%u val=%.4f",x,val);
> }
>
> When usart receive some data (usart interrupt routine does some
> integer calculations, only integer, not float) sometimes I get
> randomly wrong values from sqrtf():
> x=0 val=0.0000
> x=19 val=19.0000
> x=1 val=1.0000
>
> I suspect some reentrancy problems, becouse when usart doesn't receive
> any chars, sqrtf always return 141.4214
> As I metioned above libsdcc and lib are compiled with --stack-auto, so
> all helper (int/float) functions should be reentrant...
>
> regards,
> ml
>
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