Switch from ADSP-218X to Blackfin?

"Jon Harris" <goldentully@hotmail.com> wrote in message
news:c10f9l$1cfo62$1@ID-210375.news.uni-berlin.de...
>snip<
> Also, keep in mind that in general the Blackfins run at a
significantly
> higher clock rate than the SHARCs.  If you don't need the 32-bit
precision
> or floating point of the SHARC, you end up paying the price both in
> increased cost and slower clock speed.  On the other hand, if you
have to do
> a lot of double-precision work with a 16-bit part, the 32-bit part
will
> almost assuredly end up being faster despite the slower clock rate.
>
>
A 32-bit multiply on the Blackfin reputedly takes 5 clocks.

Regards
    Ian

"Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
news:1077182391.61573@cswreg.cos.agilent.com...
>
> >
> ADI say that the speed difference between assembler and a HLL on
> the Blackfin is around 3:1.
>
> Regards
>     Ian
>

Wow! I always expect some difference between assembly and a HHL but 3:1 is
huge IMO. Any idea why?

Regards,
Ray

"kansas_ray" <kansas_ray@hotmail.com> wrote in message
news:IJ3Zb.981$vd6.496@newssvr22.news.prodigy.com...
>
> "Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
> news:1077182391.61573@cswreg.cos.agilent.com...
> >
> > >
> > ADI say that the speed difference between assembler and a HLL on
> > the Blackfin is around 3:1.
> >
> > Regards
> >     Ian
>
> Wow! I always expect some difference between assembly and a HLL but 3:1 is
> huge IMO. Any idea why?
>
> Regards,
> Ray

An overall average number may not be all that useful.  There is probably
quite a large amount of variability based on your particular HLL code, your
skill in writing optimized assembler, etc..

"Jon Harris" <goldentully@hotmail.com> wrote in message
news:c12vaf$1dprhq$1@ID-210375.news.uni-berlin.de...
> "kansas_ray" <kansas_ray@hotmail.com> wrote in message
> news:IJ3Zb.981$vd6.496@newssvr22.news.prodigy.com...
> >
> > "Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
> > news:1077182391.61573@cswreg.cos.agilent.com...
> > >
> > > >
> > > ADI say that the speed difference between assembler and a HLL on
> > > the Blackfin is around 3:1.
> > >
> > > Regards
> > >     Ian
> >
> > Wow! I always expect some difference between assembly and a HLL but 3:1
is
> > huge IMO. Any idea why?
> >
> > Regards,
> > Ray
>
> An overall average number may not be all that useful.  There is probably
> quite a large amount of variability based on your particular HLL code,
your
> skill in writing optimized assembler, etc..
>
>

Something doesn't compute. A look at the libraries shows very efficient C
code. AD actually gives examples of "bad" C code vs good and you would have
to try pretty hard to be bad.

Maybe Ian (or anyone) could post a URL to that quote of ADI's?

Regards,
Ray

"kansas_ray" <kansas_ray@hotmail.com> wrote in
news:m48Zb.1046$Fb7.483@newssvr22.news.prodigy.com: 

> 
> "Jon Harris" <goldentully@hotmail.com> wrote in message
> news:c12vaf$1dprhq$1@ID-210375.news.uni-berlin.de...
>> "kansas_ray" <kansas_ray@hotmail.com> wrote in message
>> news:IJ3Zb.981$vd6.496@newssvr22.news.prodigy.com...
>> >
>> > "Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
>> > news:1077182391.61573@cswreg.cos.agilent.com...
>> > >
>> > > >
>> > > ADI say that the speed difference between assembler and a HLL on
>> > > the Blackfin is around 3:1.
>> > >
>> > > Regards
>> > >     Ian
>> >
>> > Wow! I always expect some difference between assembly and a HLL but
>> > 3:1 
> is
>> > huge IMO. Any idea why?
>> >
>> > Regards,
>> > Ray
>>
>> An overall average number may not be all that useful.  There is
>> probably quite a large amount of variability based on your particular
>> HLL code, 
> your
>> skill in writing optimized assembler, etc..
>>
>>
> 
> Something doesn't compute. A look at the libraries shows very
> efficient C code. AD actually gives examples of "bad" C code vs good
> and you would have to try pretty hard to be bad.
> 
> Maybe Ian (or anyone) could post a URL to that quote of ADI's?
> 
> Regards,
> Ray
> 
> 
> 

I agree that 3x seems a little excessive. 

Most DSP programmers will use C for housekeeping functions where speed is 
not generally the issue. Using C just to avoid learning the assembly 
language is probably a bad idea.

I actually write all my DSP code in assembly. With the Sharc and 
Blackfin, C is certainly a reasonable option. I just find that DSPs have 
a rich enough assembly language that to some degree , its like trading 
one mid level language (the assembly) for another less efficient mid 
level language (C).

C is also structually less than ideal for Harvard architectures. I'm not 
anti-C in general. Like everyone else, I write a little C for other 
things.


-- 
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com

"kansas_ray" <kansas_ray@hotmail.com> wrote in message
news:m48Zb.1046$Fb7.483@newssvr22.news.prodigy.com...
>
> "Jon Harris" <goldentully@hotmail.com> wrote in message
> news:c12vaf$1dprhq$1@ID-210375.news.uni-berlin.de...
> > "kansas_ray" <kansas_ray@hotmail.com> wrote in message
> > news:IJ3Zb.981$vd6.496@newssvr22.news.prodigy.com...
> > >
> > > "Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
> > > news:1077182391.61573@cswreg.cos.agilent.com...
> > > >
> > > > >
> > > > ADI say that the speed difference between assembler and a HLL
on
> > > > the Blackfin is around 3:1.
> > > >
> > > > Regards
> > > >     Ian
> > >
> > > Wow! I always expect some difference between assembly and a HLL
but 3:1
> is
> > > huge IMO. Any idea why?
> > >
> > > Regards,
> > > Ray
> >
> > An overall average number may not be all that useful.  There is
probably
> > quite a large amount of variability based on your particular HLL
code,
> your
> > skill in writing optimized assembler, etc..
> >
> >
>
> Something doesn't compute. A look at the libraries shows very
efficient C
> code. AD actually gives examples of "bad" C code vs good and you
would have
> to try pretty hard to be bad.
>
> Maybe Ian (or anyone) could post a URL to that quote of ADI's?
>
> Regards,
> Ray
>
>
No url - that was a verbal quote from their apps engineer. He thought
3:1 was good, and expected that as the tools matured it might even
improve a little :-|
I asked the question because they were touting using HLL exclusively,
and that was what the OP seemed to be considering. A more "normal"
approach would be to use HLL for some parts and assembler for the
intensive crunching.

Regards
    Ian

"Ian Buckner" <Ian_Buckner@agilent.com> wrote in message
news:1077269665.656938@cswreg.cos.agilent.com...
>
> >
> No url - that was a verbal quote from their apps engineer. He thought
> 3:1 was good, and expected that as the tools matured it might even
> improve a little :-|
> I asked the question because they were touting using HLL exclusively,
> and that was what the OP seemed to be considering. A more "normal"
> approach would be to use HLL for some parts and assembler for the
> intensive crunching.
>
> Regards
>     Ian
>

Thanks for your response.

We are considering exclusive C programming, at least until we receive an app
that requires assembly. I'll keep an eye and ear on the 3:1 ratio issue as
we ramp up and post our findings. The much faster speed of the Blackfin
should allow us to *ease* into assembly while we learn.