S12 / MagniV MicrocontrollersのトピックProblem of doing float operation in interrupt function or interrupt called function

Problem of doing float operation in interrupt function or interrupt called function

dingding — Fri, 23 Jun 2006 21:13:18 GMT

#pragma interrupt called
void sci_cmd()
{

……
Kp=(float)(sci_rec_buffer[1]*256+sci_rec_buffer[2])*0.0001;

……
}

for example, runing aboved function in sci interrupt function, but Kp(define as float type) isn't changed. I do these in codewarrior 6.0, and on 56F807

Thank you!

Re: Problem of doing float operation in interrupt function or interrupt called function

alex_spotw — Fri, 23 Jun 2006 23:41:01 GMT

Hi:

First of all, I would not recommend doing floating point operations inside Interrupt Service Routines (ISR), because they might take too much time and you could loose characters from the serial port.

A better alternative is to wait until all data has been received and then do the calculation (outside the Interrupt).

As for your problem, you have to define Kp as volatile, so that it gets updated in the ISR. Otherwise, the compiler will optimize it out.

Regards,

Alex

Re: Problem of doing float operation in interrupt function or interrupt called function

dingding — Sat, 24 Jun 2006 14:19:52 GMT

Thanks for your help!

It does well.