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help!why not use Rx as loop counter?

I have a problem. I write a function in another c source file not main file, in this function nothing do, and I declare the function as extern. In main function I invoke it 200 times. However, the compiler does not use registerbank as counter. Why?

extern void func1(void);

void func2(void)
{
        unsigned char data i;
        for(i=200;i;i--);
}

main()
{
        unsigned char data i,j;
        for(i=200;i;i--)        // store i in 0x08
        {
                func1();
        }
        for(j=200;j;j--)        // store j in R6
        {
                func2();
        }
}
the assembly code:
C:0x0003    7508C8   MOV      0x08,#TMR2CN(0xC8)
    19:         {
    20:                 func1();
C:0x0006    120025   LCALL    func1(C:0025)
    21:         }
C:0x0009    D508FA   DJNZ     0x08,C:0006
    22:         for(j=200;j;j--)
C:0x000C    7EC8     MOV      R6,#TMR2CN(0xC8)
    23:         {
    24:                 func2();
C:0x000E    120020   LCALL    func2(C:0020)
    25:         }
C:0x0011    DEFB     DJNZ     R6,C:000E

Parents Reply Children
  • Sorry, I missed that bit.

    Anyway, yes, I think you are correct ...

    unsigned char *i, j;
    

    is equivalent to:

    unsigned char *i;
    unsigned char  j;
    

    Is it not???

    I never use the first one, precisely because someone quiclky scanning the code might make a bad assumption.

  • Keil has somehow forgotten to specify if "data" binds to the left or to the right, but their own placement of the keyword does give an indication that it binds to the variable and not to the type, i.e. that it follows Andys example.

    Compare with * for pointesrs, i.e.

    unsigned char * i,j;
    


    may look like

    unsigned char* i;
    unsigned char* j;
    


    but is actually:

    unsigned char *i;
    unsigned char j;
    

  • As you might have guessed from my replies, I also missed it initially!

    "I never use the first one, precisely because someone quiclky scanning the code might make a bad assumption."

    Absolutely. Plus all the other good reasons equivalent to always using the braces on an 'if' even when not strictly necessary...