hello world - strange variables behavior

Altera_Forum · ‎02-23-2011

Hello,

I'm new to nios2 developpement and i'm having problems running the simple hello_world exemple :

When I lauch this code :

int main()
{
  unsigned char i,j,k;
  printf("Hello from Nios II!\n");
  while(1){
      i++;
      j++;
      k++;
      if(k==100){
       printf("a"); 
      }
  }
  return 0;
}

in the debugger, i can see that the 'i' variable is incrementing correctly, but the 'j' variable always have the value 203 and the 'k'variable always have the value 0.

Although i cant see the 'k' value changing, the program does go in the if statement.

Could anyone explain to me why i cant monitor correctly the variables values?

Thanks

ps: running this program, i also have an other problem regarding the console ouput as described in this post : alteraforum.com/forum/showthread.php?t=27499. I supposed it could be related

Altera_Forum · ‎02-23-2011

Quite possibly the values are in registers and/or optimised away.

Altera_Forum · ‎02-23-2011

but why can I read 'i' correctly but not 'j' and 'k' ?

The thing is, i noticed this problem is some other project where i really needed to read back some avalon-slave-module registers values. I was getting really strange values so i then tried to run the simple hello_world on my board to see if i still had problems.

could the problem come from a bad sopc builder configuration ?

Altera_Forum · ‎02-23-2011

Look at the generated code...

gdb can't really guarantee to give you the values of variables that are in registers.

Although if you aren't compiling with -O2 (you really should use -O2 or -O3) then it is likely that all the expected code (including all the load/stores from stack for the local variables) is actually generated.

Marking global data 'volatile' will force all references in the C source to generate load/store instructions.