> >
> >The article is in Scott Edward's April 1996 "Stamp Applications" of Nuts &
> >Volts.
> >
> >In it, Scott shows the section of code:
> >
> >  again:
> >   b1 = b1 + 1                  ;  increment b1
> >   toggle 0                     ;  toggle pin 0
> >   goto again
> >
> >and then goes on to give the following performance results:
> >
> >  BS1, 4 MHZ            479 Hz
> >  .
> >  :
> >  16C84, compiled 4 MHZ 7215 Hz
> >
> >
> >Now, my thought was that any decent compiler would produce the following
 code:
> >
> >again
> >  incf   b1                     ;  increment b1
> >  movlw  0x01                   ;  toggle pin 0
> >  xorwf  PORTB                  ;  Assume pin 0 is in PORTB
> >  goto   again
>

> >This can be improved to:
> >
> >  movlw  0x01                   ;  Setup Pin to Toggle
> >again
> >  incf   b1                     ;  increment b1
> >  xorwf  PORTB                  ;  toggle pin 0
> >  goto   again
>
> Yep this would be real nice. :)
>
> >Although while I would expect this type of optimization for a workstation
> >compiler, I wouldn't think that it would be reasonable for a Hobbyist one.
> >
> >The first loop takes five instruction cycles to run (the second four) - five
> >instructions running at 4 Mhz (1 MHz Instruction cycle frequency) means that
> >the loop would run at 200 KHz.

I think the output would be more likely to be 100KHz. 5 instructions on and 5
instructions off.

>
> I checked our multi-target Basic compiler with PIC as target with your
> code and got 50 KHz for the same loop.

I just checked the MPC compiler and it generates the 5 instruction sequence
 first
shown above.

One of our other compilers surprised me with the following code sequence
 equivalent.


      movlw  0x01                   ;  Setup Pin to Toggle
again
      xorwf  PORTB                  ;  toggle pin 0
      goto   again

The missing increment was caused by a default non-volitile variable that was
 never
again referenced in the program. Its value did not matter.

True comparitive benchmarks are tough to write.

Walter Banks