F2MC-16LX How to make the ROM efficient C source

Version: **

 

Answer:

 

 

  1. Using the _direct declaration (C Analyzer enables to detect candidate for efficient _direct.)
      To improve the ROM code efficiency of C source, it is possible to improve by defining static variables as _direct declaration ones.
      The _direct declaration variables are in 256Byte (min.). It is efficient way to define frequent used variables as _direct declaration in order.
     
      direct declaration sample:
     
      _direct unsigned char port_new,port_old,port1_data;
      _direct unsigned int time;
      void main(void)
      {
           port_new=0;
           port_old=10;
           port1_data=0xff;
           init_CPUstate();
        while(1)
       {
           search_state();
           port1_data--;
                :
                :
           for(time=0;time<=1000;time++);
       }
      }
      
  2. Using the in-line. (C Analyzer enables to detect candidate for in-line expansion.)
      When defining the function of the small code size with argument as static function and implementing in-line expansion, which allow to reduce the code size.
     
      To implement in-line expansion of static declaration function, the -xauto option need specifying before compiling the source program.
     
      Example of in-line expansion:
      static Proc7 (IntParI1, IntParI2, IntParOut)
      OneToFifty IntParI1;
      OneToFifty IntParI2;
      OneToFifty *IntParOut;
      {
      REG OneToFifty IntLoc;
     
      IntLoc = IntParI1 + 2;
      *IntParOut = IntParI2 + IntLoc;
      }
      
  3. Using the built-in function
      When performing a multiplication and a division by C language, the code size is too big bye using the libraries of div/mul/mod.
     
      Therefore F2 MC-16LX family allow to use these built-in functions of _mul( )/_div( )/_mod( ). These functions enables to reduce the code size.
     
      Example of built-in function:
      unsigned int a,b;
      unsigned long c;
     
      void sample(void)
      {
      //  c=a*b;              /* normal description of C language */
          c=_mul(a,b);     /* description of using built-in function */
      }