Data aquistion problem

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Hi Folks,

I need to caputure 64 bits data at 66 Mhz, that makes 533 Mbytes a
sec, for at least a few sec. Is there any data aquisition system out
there that could do the job, maybe even a PC based one?

Best Regards,
Roel

Re: Data aquistion problem
Hi Roel,

If this is a multi-channel AD conversion job I would talk to an engineer
at Gage, Inc. Chances are, if they can't do it there may be nothing else
around that does. Of course you could always build you own.

Regards, Joerg

http://www.analogconsultants.com

Re: Data aquistion problem
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The actual number behind "a few" could easily make the difference
between easy and way out of league, there.  Suffice it to say that if
you can't afford enough Gigabytes of RAM to cache the entire "few"
seconds' worth of data, you're looking at a massively parallel array
of mass storage devices (e.g. ~20 modern harddrives in parallel might
do it).

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Sure.  High-energy physics experiments handle rates even larger than
that, even for essentially indefinite periods of time.  But you may
not want to see what such systems cost.

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No way.  No accessible port an a vanilla PC has anywhere near 500 MB/s
of bandwith.  64bits at 66Mhz is the nominal width of a server-grade
PCI-X/66 port, but you won't find that on anything that would still
qualify as "PC-based", i.e. attachable to a reasonably typical PC.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Data aquistion problem
Hello Hans-Bernhard,

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It's not so bad. I recently bought a storage card for my camera and paid
$40 for 256MB. Now they sell 512MB for the same price so memory costs
should not be a huge issue here. Considering chips or RAM modules
instead of these cards the difference between a few seconds or a few
more should not be much above $100.

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He'd have to buy a card with huge memory on board, store it there and
then send it via the PC bus at regular bus speeds. I believe that is how
Gage does it with their top of the line PC data acquisition cards. That
would be the first company I'd contact in such a situation.

Regards, Joerg

http://www.analogconsultants.com

Re: Data aquistion problem
[You snip my attribution, I snip yours...]

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Flash RAMs are quite completely beside the point.  We're talking about
datarates well beyond anything those 40$ cards will handle.

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You come back saying that again when you've found a motherboard that
can handle more than 3 GB of memory that is remotely compatible with
the price range of an ordinary PC.

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I would slightly object to calling such a setup "PC-based" without
further qualification.  Such a beast (if you can find one that holds
well above 1 Gigabyte) would essentially be a standalone solution that
just interfaces a bit more closely with the PC than it strictly has
to.  It might prove quite tricky to supply 8 GB of sufficiently fast
DRAM off a simple PC slot.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Data aquistion problem
Hello Hans-Bernhard,

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That's ok, you can. I do that to keep things brief so that readers who
click from one post to the other don't have to scroll through everything
a gazillion times. The only quotes I leave in are those where I believe
they are needed to understand my post.

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I only mentioned these to make the point that memory is cheap nowadays.
Very cheap.

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Ok, I am back. Not with a motherboard since most motherboards aren't
made to handle this much data. But hard drives are. You need to store on
the PC card first, then transfer. If you want to see what I mean look at
this PCI card:

http://www.gage-applied.com/products/digital/compuScope_3200.htm

I am pretty sure you can gang two of them and, bingo, there is the bus
width Roel needs and up to 4GB total memory on board. Of course the
details such as ganging, synchronization etc. need to be thoroughly
discussed with the card manufacturer. If you need to acquire analog data
they also have cards with 2GB on board. Here is an example of a fairly
regular analog card that can hold 2GB:

http://www.gage-applied.com/products/digitizer_pci/8_bit/compuScope_8500.htm

We have used such Gage products in ordinary PCs many times, usually in
production or quality control applications.

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You could call it standalone but the main thing is that it could work in
Roel's application. Just as a side note, I did see a regular but "souped
up" PC that had an incredible amount of memory installed, several
gigabytes. It was used in a video processing setup. Nowadays even
laptops such as a Dell Inspiron XPS can be had with 2GB of RAM if you
want to.

Regards, Joerg

http://www.analogconsultants.com

Re: Data aquistion problem

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"Store on the PC card" means you move the memory requirement to a
different place: from the motherboard to dedicated hardware.  Which
brings us back to may gripe about what can still appropriately be
called a "PC-based" solution, since during the actual activity, the
host PC is really just sitting there doing nothing.  I.e. the PC
is not the base of such a solution, it just plays host to the party.

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It takes quite a bit more than a bit of "soup-up" to make a regular PC
applicable for this kind of work.  For starters, you need completely
different mainboards (server/"workstation" type), and most users will
have to invest in a new operating system, too: Windows below the
server-grade versions doesn't support more than about 4 GB of actual
RAM.

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2 GB isn't a major problem (well, if we set aside the power
consumption draining the battery).  5 GB, however, definitely would
be.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Data aquistion problem
Hello Hans-Bernhard,

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True, it may not be the PC who does the main work. It does though once
the data has been transferred to RAM and/or hard disk. But the main
thing I'd see in this case is whether it would be enough for what Roel
wants to do. If it works for him, who cares whether it is fully or only
partially PC based.

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Well, I wouldn't try this kind of stuff with some Windows home edition.
But it isn't such a big deal to buy the server edition.

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Agree, anything above 4GB is a problem in a 32 bit system. PAE gets
around that by mapping and I believe that's what they did on the video
processing PC that I mentioned which had far more than 4GB. But to truly
run a fast and direct access to more than 4GB would require a transition
to a 64 bit system.

Again, Roel might not have to do that. If, for example, these huge
amounts of data are recorded to catch some event he could transfer
overlapping 1GB segments to RAM and have his software comb through that
data. Heck, we even did similar stuff in the DOS days. It is comparable
to a Holter ECG where a patient's heart signals are monitored for days
and then all that data is parsed to find events such as a suspicious
fibrillation.

Regards, Joerg

http://www.analogconsultants.com

Re: Data aquistion problem
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The problem is not the RAM itself.  A raw data rate of 533 MB/s is,
indeed, manageable by the core components of any modern PC.  The
problem is that none of the available *ports* are anywhere as wide as
that.  The necessary bandwidth is available only on internal
connections among chipset, RAM and CPU.

Let me remind you that PCs of current design (before PCI-Express)
failed to support even the much lower 125 MB/s needed by Gigabit
Ethernet via any of the existing ports, until chipsets were extended
by a dedicated port for just that usage.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Data aquistion problem
Hi Roel

What you probably need is dedicated hardware.
A memory buffer with a word size of 64 bits on
the input side and any word size on the output
side to read the the buffer's contents at a leisure.
This'll remove the need for extremely fast memory
while retaining the required bandwidth.

Now for the memory size: let's assume that your
experiment takes at most 5 seconds and that
your data arrives with a frequency of 100 MHz
(makes the calculation easy and yup, we'll allow
for some slack here and furthermore, you may
never know what the future may bring ;-)
Thus, data arrives every 10 nsec. (My uneducated
guess is that there numerous manufacturers who
supply memory with access times much less than
that.) One second of measurement yields 100 M
of 64 bit words (= 800 Mbytes), therfore 5 seconds
will give you 4 Gbytes of data.

Greetz

Waldemar

----- Original Message -----
Newsgroups: comp.arch.embedded
Sent: Friday, October 22, 2004 5:54 PM
Subject: Data aquistion problem


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Re: Data aquistion problem
On Sun, 24 Oct 2004 11:17:16 +0200, "WaldemarIII"

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Some DRAM structures may also allow writing multiple consecutive words
without changing the high address bits, thus quite high sequential
write rates can be achieved, but of course, you sometimes have to use
the full RAS/CAS cycle, so some short time buffering is also needed.
Also some time must also be allocated for refresh.

Since it is unlikely to find 4 GB memory modules, multiple modules
will be needed anyway, so the memory word length can be easily
extended to 256 to 1024 bits and write 4-16 samples at a time or in an
overlapped way, thus allowing for quite slow memory cycle times.

Paul
  

Re: Data aquistion problem
On 22 Oct 2004 08:54:58 -0700, electronics snipped-for-privacy@hotmail.com (Roel)

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If the dedicated hardware is not appealing and you want to use some PC
systems, one alternative solution would be to use eight separate PCs
with 8 bits digital input at 66 Mbytes/s or 64 PCs with 1 bit at 66
Mbits/s or 8,25 Mbytes/s. Of course you will need some synchronisation
signals.

Using multiple PCs might be an option, if this is a one-off project
and the system is required only for a limited time (a few months).
Thus, the PCs could be purchased, used for the experiment and then
"sold" to the other part of the organisation for normal desktop use.

Paul


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