"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:6-GdnUhT-pXGSgvfRVn-3g@comcast.com...
> Alex Gibson wrote:
>
> (snip)
>
>> Make sure to include the price of the software unless
>> you are at a university (can request it free from the xilinx university
>> program).
>
> Xilinx now has a free version that does many, though not all, of the
> chips that they make. It is, at least, enough to learn how to do it.
> It includes the simulator so you can test out designs.
>
> -- glen
>
Reply by glen herrmannsfeldt●May 27, 20052005-05-27
Alex Gibson wrote:
(snip)
> Make sure to include the price of the software unless
> you are at a university (can request it free from the xilinx university
> program).
Xilinx now has a free version that does many, though not all, of the
chips that they make. It is, at least, enough to learn how to do it.
It includes the simulator so you can test out designs.
-- glen
Reply by Alex Gibson●May 27, 20052005-05-27
"Mike" <mail2mz@gmail.com> wrote in message
news:1116948847.214232.269800@g49g2000cwa.googlegroups.com...
> Sorry to confuse everyone. Actually I am trying to compare the Pros and
> Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
> like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
> think both of them are able to complete a 128 pt or 256 pt fix point
> FFT. What I don't know are the price, speed and any other concern.
>
> Thanks,
>
> Mike
>
Make sure to include the price of the software unless
you are at a university (can request it free from the xilinx university
program).
Can be quite a large and long learning curve if you have not used fpgas
before.
For the fpga
Going to do your own fft or buy a ip an ip core ?
eg http://www.andraka.com/cores.htm
for xilinx
Need Xilinx ise and xilinx system generator
(maybe a good idea to stay away from ise7.1 )
http://www.xilinx.com/products/design_resources/dsp_central/grouping/index.htm
Spartan3 up to 1.5 mil gates can be use with the free webpack tools
For altera
Quartus2 + dsp builder
http://www.altera.com/technology/dsp/dsp-index.jsp
Alex
Reply by ●May 26, 20052005-05-26
"Michael Schoeberl" <nospam-newsgroups@michael-schoeberl.de> escribi� en el
mensaje news:4293a245$1_2@news.eticomm.net...
> > For FPGA I would like to use Xilinx's chip.
>
> hmm ... I hope you are at least talking about Spartan2 (or above - Spartan
> 2E for example)
>
> > What I don't know are the price, speed and any other concern.
>
> the chip is cheap (XC2S150E is 22$ at digikey@90pc) but do you have the
> developement tools and the knowledge?
> can you live without a multiplication?
> can you build the interface to you data-source? (unfortunately this is
> usually more complicated)
Spartan3 parts are even nicer: XC35200 is between $15 and $17 at Avnet
(couldn't find at Digikey) in unit quantities.
Multiplicators are included on chip.
--
------------------------------
Jaime Andr�s Aranguren Cardona
jaac@sanjaac.com
SanJaaC Electronics
Soluciones en DSP
www.sanjaac.com
Reply by Michael Schoeberl●May 24, 20052005-05-24
> For FPGA I would like to use Xilinx's chip.
hmm ... I hope you are at least talking about Spartan2 (or above -
Spartan 2E for example)
> What I don't know are the price, speed and any other concern.
the chip is cheap (XC2S150E is 22$ at digikey@90pc) but do you have the
developement tools and the knowledge?
can you live without a multiplication?
can you build the interface to you data-source? (unfortunately this is
usually more complicated)
Price:
I think you can get Spartan 2E chips from XC2S50E (few logic) up to
XC2S600 (lots of logic elements) ... the price/availability has more
fluctuation between vendors than in the family ...
(last year we had a factor 2 in price and 18 weeks of waiting difference
for a bigger Xilinx FPGA part)
Speed:
for the FPGA you can have everything ...
- you could implement a general purpose CPU and calculate the fft on
that (will be really slow - but there are free CPUs and you will soon
have results ;-)
- you could take the xilinx Core generator and use a ready made fft
module (license $$)
- there is a fft core on opencores.org ... "a 1024 point 12 bit FFT runs
at about 97MHz in a Spartan2e100 -6 device and occupies about 52% of the
device." ... but they don't say how long it will take for one block
(and I haven't seen a 128 point fft)
- you can write your own, fully pipelined parallel fft - you can almost
any throughput - the limit is memory bandwidth (and the fact, that the
latency is not as easy to be reduced)
other concerns:
- If you are new to hardware, you need 1/2 year for learning the FPGA
developement ... thats more expensive than the chip
the DSP is easier for getting it going ... if you need more speed then
you need the fpga (and a lot more time)
are you actually trying to build something? just a prototype? a real
product with > 100k? or is it just a comparison for a paper ..?
bye,
Michael
Reply by glen herrmannsfeldt●May 24, 20052005-05-24
Mike wrote:
> Sorry to confuse everyone. Actually I am trying to compare the Pros and
> Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
> like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
> think both of them are able to complete a 128 pt or 256 pt fix point
> FFT. What I don't know are the price, speed and any other concern.
It is exactly the price and speed you need to know.
If the DSP is fast enough, that will most likely be the best solution.
If not, then you either need multiple DSP or FPGA. For the FPGA case,
either a fairly large one or multiple chips. The FPGA solutions will
tend to scale to larger arrays fairly easily, for example a systolic
array solution should be possible where a longer array will do longer
transforms at a give clock rate. If you don't need one result per
clock cycle, you might be able to do some sharing of hardware between
different parts of the algorithm.
-- glen
Reply by Tim Wescott●May 24, 20052005-05-24
Bhaskar Thiagarajan wrote:
> "Mike" <mail2mz@gmail.com> wrote in message
> news:1116948847.214232.269800@g49g2000cwa.googlegroups.com...
>
>>Sorry to confuse everyone. Actually I am trying to compare the Pros and
>>Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
>>like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
>>think both of them are able to complete a 128 pt or 256 pt fix point
>>FFT. What I don't know are the price, speed and any other concern.
>
>
> Still not good enough in the information dept to be able to provide
> meaningful answers.
> What is the input sample rate of the data, what is the max clock speed you
> are going to be able to run your FPGA and your DSP?
> It feels like you have a lot more learning to do before our answers can
> really be of any use to you (even after you provide all the information). If
> it feels like we are belitttling you, our apologies.
>
> Cheers
> Bhaskar
>
>
To rephrase your question:
"I have some cargo to take across the lake. Do I need a rowboat, a
powerboat, or a freighter?".
To rephrase Baskar's reply:
Is your cargo a cup of sugar or 100 shipping containers thereof? Is the
lake is 100 yards across or is it Lake Superior? How soon does your
cargo need to get across the lake?
Do you see our problem here?
--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Tim Wescott●May 24, 20052005-05-24
Mike wrote:
> Sorry to confuse everyone. Actually I am trying to compare the Pros and
> Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
> like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
> think both of them are able to complete a 128 pt or 256 pt fix point
> FFT. What I don't know are the price, speed and any other concern.
>
> Thanks,
>
> Mike
>
An n-point FFT requires something on the order of n*log(n) multiplies
and adds. Figure that the TI chip is going to require something on the
order of 5-20 clock ticks * n * log_2(n) to get it done (someone will
want to refine that figure, which is good because I haven't actually
coded an FFT on a DSP). An FPGA will do whatever you design it for,
with a _BIG_ tradeoff between speed, logic utilization, and engineering
time -- e.g. with a big enough FPGA you could do an n-point FFT in
log_2(n) steps, but it'd have to have 2n multipliers to do it.
Check the archives of places like Electronic Design News, Electronic
Design, possibly look for whitepapers on the TI and Xilinx websites --
there's a lot more information that you need than we can answer here in
reasonable length posts.
--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Bhaskar Thiagarajan●May 24, 20052005-05-24
"Mike" <mail2mz@gmail.com> wrote in message
news:1116948847.214232.269800@g49g2000cwa.googlegroups.com...
> Sorry to confuse everyone. Actually I am trying to compare the Pros and
> Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
> like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
> think both of them are able to complete a 128 pt or 256 pt fix point
> FFT. What I don't know are the price, speed and any other concern.
Still not good enough in the information dept to be able to provide
meaningful answers.
What is the input sample rate of the data, what is the max clock speed you
are going to be able to run your FPGA and your DSP?
It feels like you have a lot more learning to do before our answers can
really be of any use to you (even after you provide all the information). If
it feels like we are belitttling you, our apologies.
Cheers
Bhaskar
> Thanks,
>
> Mike
>
Reply by Mike●May 24, 20052005-05-24
Sorry to confuse everyone. Actually I am trying to compare the Pros and
Cons for the implemetation of FFT using DSP or FPGA. For DSP, I would
like to us TI's chip; For FPGA I would like to use Xilinx's chip. I
think both of them are able to complete a 128 pt or 256 pt fix point
FFT. What I don't know are the price, speed and any other concern.
Thanks,
Mike