while statement problem

Hi,

I assume you are writing in C? "and" is not a keyword, use "&&" instead.

regards

spachner

Thanks a lot! That's it!

Another problem i have:

volatile struct
{
  unsigned ToggBit: 1;  

  unsigned Value: 1;       
}
rc5bits;

while((P1IN&BIT5 == rc5bits.Value) && (BD1 < OK))   

{ //do something }

i get a warning:

Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement

The volatile qualifier is a way of telling the compiler that the value of the variable can change at any time. When you compare two volatiles, both have to be read in order to do the comparison, but they could be read in any order and could change at any time. The compiler warning is basically to say that the order of accessing the volatiles is undefined and that can have an impact upon the results of the comparison.

A google search on that error produces a couple of results that give a good explanation in the MSP430 discussion groups in http://www.embeddedrelated.com. Note that although they may reference the IAR compiler, the TI compiler's parser also does the same thing.

When I use the expression (v+v) where v is volatile, the compiler also gives the same warning.

Because v is volatile, it has to be read twice, once for the v after the left-(, and once for the v before the right-). In this case, does it matter which v is read first? Isn't first-V plus  second-v the same as second-v plus first-v? Why the warning in this case?

Thank you. Now it's clear for me.