Back to Know-How on Development for F²MC-16LX Family

2. How to make the ROM efficient C source

2-1. 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++);
 }
}

2-2. 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;
}

2-3. 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 */
}

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