text: // passing around global arrays as args
  extern void echo(int);
  
  volatile int x[2];
  
  void write_arr(int *x, int n) {
    x[0] = n;
    x[1] = n+2;
    return;
  }
  
  void read_arr(int x[2]) {
    int y = x[0];
    echo(y);
    y = x[1];
    echo(y);
    return;
  }
  
  int main() {
    write_arr(x,0);
    read_arr(x);
    write_arr(x,1);
    read_arr(x);
  }
  