Lpc2000

At 01:35 PM 12/13/05 +1300, Charles Manning wrote:
>On Tuesday 13 December 2005 11:36, uedogan wrote:
> > Hi everybody,
> >
> > i'm currently working with the LPC2136 and the latest KEIL C-compiler.
> > Does anybody know some functions that provide a (much) faster 16-bit
> > unsigned integer division than KEIL currently has? I have ~58MHz and
> > the division currently needs about 2us.
> > I would even prefer some 32-Bit unsigned integer divisions but these
> > run totaly out of my available timing (KEIL needs ~3.9us for that).
>
>OK, I have not tried this out, but I'm quite surprised  it takes soooooo 
>long.
>Keil have a good reputation and I would have expected a better result than
>this.
>
>I looked at the gcc code for divi3 and it is approx 256 bytes long, but not
>all of that is getting executed. I would expect this to run faster than the
>numbers you give.

That is not be the worst of it.  I did some indirect measurements of 
division time when working up the second revision of the timing support in 
the newlib-lpc library.  (See 
http://www.aeolusdevelopment.com/AppNotes/LPC210X/an-timerperformance.pdf 
for some of the details if you're interested)  Not only does the division 
take a significant amount of time but the length of time it takes varies 
significantly depending on the values used.  Clearly the algorithm is 
optimized to shortcut out quickly.  Normally that's a good thing but 
sometimes....

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/