large FIFO buffer?

A

Adam Kumpf

Guest
Hello all,

I am in the middle of laying out a design for a medical device the reads
in data pretty quickly (~20MHz) in bursts, but is limited to a slow serial
connection to transfer the data. The solution that comes to my mind is a
large FIFO buffer (~100k+) that can take an 8-bit parallel input, but I
can't find them anywhere in a reasonable price range. I've looked all over
at the common manufactures of logic devices (TI,nationalsemi) and some
distributors (digikey,mouser) but can't find much. I hear of hard drives
with 512k buffers/caches quite commonly. what am I missing here?

Does anyone know of a model/part# of a pretty high speed, 100k+ fifo
buffer?

Thanks in advance for your help.

Best Regards,
Adam Kumpf
kumpf@mit.edu
http://web.mit.edu/kumpf/www/kumpf-projects.html
 
On Sun, 13 Mar 2005 12:53:13 -0500, Adam Kumpf wrote:

Hello all,

I am in the middle of laying out a design for a medical device the reads
in data pretty quickly (~20MHz) in bursts, but is limited to a slow serial
connection to transfer the data. The solution that comes to my mind is a
large FIFO buffer (~100k+) that can take an 8-bit parallel input, but I
can't find them anywhere in a reasonable price range. I've looked all over
at the common manufactures of logic devices (TI,nationalsemi) and some
distributors (digikey,mouser) but can't find much. I hear of hard drives
with 512k buffers/caches quite commonly. what am I missing here?
Click to expand...
FIFOs are fairly unique parts, so don't have the price pressure of more
standard devices. SRAMs are dirt cheap, for example. Disk drives don't
use large FIFOs for buffers.

Does anyone know of a model/part# of a pretty high speed, 100k+ fifo
buffer?
Click to expand...
I'd use a programmable device (FPGA, probably). Since your
requirements are for a significant chunk of memory (an FPGA with that
much would be expen$ive), I'd use an external SRAM on a smaller
programmable device. 50MHz shouldn't be *too* hard with current devices.
The only scary part of the design is "medical device". ;-)

--
Keith
 
keith wrote:
On Sun, 13 Mar 2005 12:53:13 -0500, Adam Kumpf wrote:

I am in the middle of laying out a design for a medical device the reads
in data pretty quickly (~20MHz) in bursts, but is limited to a slow serial
connection to transfer the data. The solution that comes to my mind is a
large FIFO buffer (~100k+) that can take an 8-bit parallel input, but I
can't find them anywhere in a reasonable price range.
[snip]
Does anyone know of a model/part# of a pretty high speed, 100k+ fifo
buffer?

I'd use a programmable device (FPGA, probably). Since your
requirements are for a significant chunk of memory (an FPGA with that
much would be expen$ive), I'd use an external SRAM on a smaller
programmable device.
Click to expand...
I agree that a "roll your own" FIFO is the way to go, if production cost
is your major concern. You should be able to fit this into a CPLD with
128 macrocells, unless you have other requirements that make the control
logic particularly complex. This will remove the need for powerup
programming of an FPGA. OTOH, using an FPGA that is programmed by your
processor allows you to easily modify the code in the field, assuming
your product will be designed for software field upgrades anyway.

I know Xilinx has proven code available for FIFOs and I think Altera
does as well, although these probably assume the RAM is internal and
dual-ported. You can check at opencores.org to see how their FIFO fits
your app but you may not like the licensing issues.

50MHz shouldn't be *too* hard with current devices.
Click to expand...
50 MHz should be no problem at all for either a CPLD or FPGA of the
current generation. I've been doing 133 MHz FIFOs inside FPGAs for
several years now.

The only scary part of the design is "medical device". ;-)
Click to expand...
Ooo-ooo-oo . . . (involuntary shudder), just the thought of the
liability makes my toes curl. ;-)

On that note, please apply all the usual disclaimers about me not being
liable for *anything* as a result of your use of my completely
uninformed and most likely incorrect suggestions. (want to put a smiley
here but I'm too afraid of the lawyers)
--
Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer
Marmot Engineering . . . . . . . VHDL, ASICs, FPGAs, embedded systems
Vancouver, BC, Canada . . . . . . . . . . . http://www.marmot-eng.com
 
keith wrote:
On Sun, 13 Mar 2005 12:53:13 -0500, Adam Kumpf wrote:


Hello all,

I am in the middle of laying out a design for a medical device the reads
in data pretty quickly (~20MHz) in bursts, but is limited to a slow serial
connection to transfer the data. The solution that comes to my mind is a
large FIFO buffer (~100k+) that can take an 8-bit parallel input, but I
can't find them anywhere in a reasonable price range. I've looked all over
at the common manufactures of logic devices (TI,nationalsemi) and some
distributors (digikey,mouser) but can't find much. I hear of hard drives
with 512k buffers/caches quite commonly. what am I missing here?


FIFOs are fairly unique parts, so don't have the price pressure of more
standard devices. SRAMs are dirt cheap, for example. Disk drives don't
use large FIFOs for buffers.


Does anyone know of a model/part# of a pretty high speed, 100k+ fifo
buffer?


I'd use a programmable device (FPGA, probably). Since your
requirements are for a significant chunk of memory (an FPGA with that
much would be expen$ive), I'd use an external SRAM on a smaller
programmable device. 50MHz shouldn't be *too* hard with current devices.
The only scary part of the design is "medical device". ;-)
Click to expand...
If it were me I'd also check to see if you ever need to read data in and
out simultaneously -- if you can either acquire all of a burst then read
it all out entire, or if you can at least pause the readout while a
burst is coming in then you'll massively simplify your FIFO design.

As mentioned by the OP, since this is a medical device none of the
information I'm giving you should be taken as reliable, it's all made up
on the spur of the moment, YMMV, IMHMHUMA, etc.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
haha.. no worries about legal issues.. just trying to get a quick prototype
up and running for proof of concept. Everything will be thoroughly verified
before any production level circuitry is decided upon. :)

Thanks for all of your help. The SRAM decision only slightly complicated
the design, but reduces the price drastically(by a factor of 10 or more!)...
just what I was looking for! :)

Thanks again.

Best Regards,
Adam Kumpf



"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1139a9l3n79rhf9@corp.supernews.com...
keith wrote:
On Sun, 13 Mar 2005 12:53:13 -0500, Adam Kumpf wrote:


Hello all,

I am in the middle of laying out a design for a medical device the
reads
in data pretty quickly (~20MHz) in bursts, but is limited to a slow
serial
connection to transfer the data. The solution that comes to my mind is
a
large FIFO buffer (~100k+) that can take an 8-bit parallel input, but I
can't find them anywhere in a reasonable price range. I've looked all
over
at the common manufactures of logic devices (TI,nationalsemi) and some
distributors (digikey,mouser) but can't find much. I hear of hard
drives
with 512k buffers/caches quite commonly. what am I missing here?


FIFOs are fairly unique parts, so don't have the price pressure of more
standard devices. SRAMs are dirt cheap, for example. Disk drives don't
use large FIFOs for buffers.


Does anyone know of a model/part# of a pretty high speed, 100k+ fifo
buffer?


I'd use a programmable device (FPGA, probably). Since your
requirements are for a significant chunk of memory (an FPGA with that
much would be expen$ive), I'd use an external SRAM on a smaller
programmable device. 50MHz shouldn't be *too* hard with current devices.
The only scary part of the design is "medical device". ;-)


If it were me I'd also check to see if you ever need to read data in and
out simultaneously -- if you can either acquire all of a burst then read
it all out entire, or if you can at least pause the readout while a
burst is coming in then you'll massively simplify your FIFO design.

As mentioned by the OP, since this is a medical device none of the
information I'm giving you should be taken as reliable, it's all made up
on the spur of the moment, YMMV, IMHMHUMA, etc.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Click to expand...
 
Averlogic have nice big fast FiFo's

and the price is pretty good

http://www.averlogic.com/

Greezt,

Markus
 
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