Incorporating FPGAs on PCBs

Hi,

	I need to interconnect two or four FPGAs on a PCB, and I am looking
at the prospect of designing these boards myself. If any one has done
this, I would be grateful if you could provide some pointers,
especially links to websites that have this information. I would
probably be using the Xilinx Virtex II

	I don=92t know how to start this =96 but I have a few questions. Is it
possible for me to simulate the setup between FPGAs connected on a PCB
board. Or is it possible for me to bread board the FPGA =96 I have not
heard of this though. I have looked at the manual of the Virtex II,
and there are a large numbers of pins =96 I have yet to figure out which
pins I need to power at the minimum to get this to work. So I don=92t
want to start laying out a PCB Board immediately.

	I would be requiring significant on board communication =96 but I don=92t
think I need the Rocket IOs that are available with Virtex4 =96 the
simple LVDS would do for me I guess. Is there a way for me to test
this aspect before actually putting it on the PCB??

	I have so far used FPGAs on the protyping board that comes with the
Spartan Kit from Xilinx. I have also used an Emulation machine with a
couple of FPGAs. In all of this I have never been concerned about the
external connections between FPGAs, so I am new to all of this.

Any help is welcome.

Thanks a lot.
O.O.

Hi,

why would you want to use Virtex-II on a new board? They are more
expensive than the newer parts. Check out the various Spartan-3
variants and Virtex-5LX.

You need to supply power more or less to all power pins and you
definitely should use a board with at least 4 layers.

Kolja



On 16 Mai, 11:29, "O. Olson" <olson_...@yahoo.it> wrote:
> Hi,
>
>         I need to interconnect two or four FPGAs on a PCB, and I am lookin=
g
> at the prospect of designing these boards myself. If any one has done
> this, I would be grateful if you could provide some pointers,
> especially links to websites that have this information. I would
> probably be using the Xilinx Virtex II
>
>         I don=92t know how to start this =96 but I have a few questions. I=
s it
> possible for me to simulate the setup between FPGAs connected on a PCB
> board. Or is it possible for me to bread board the FPGA =96 I have not
> heard of this though. I have looked at the manual of the Virtex II,
> and there are a large numbers of pins =96 I have yet to figure out which
> pins I need to power at the minimum to get this to work. So I don=92t
> want to start laying out a PCB Board immediately.
>
>         I would be requiring significant on board communication =96 but I =
don=92t
> think I need the Rocket IOs that are available with Virtex4 =96 the
> simple LVDS would do for me I guess. Is there a way for me to test
> this aspect before actually putting it on the PCB??
>
>         I have so far used FPGAs on the protyping board that comes with th=
e
> Spartan Kit from Xilinx. I have also used an Emulation machine with a
> couple of FPGAs. In all of this I have never been concerned about the
> external connections between FPGAs, so I am new to all of this.
>
> Any help is welcome.

Thanks for pointing this out that the Virtex II might be costlier than
newer parts.

	I understand that powering up of the power pins should do =96 however
there are so many pins and it is possible for me to make a mistake. Is
there some tools that can verify this =96 or allow me to simulate this,
so that I don=92t make obvious mistakes. I don=92t think that the
developers of FPGA Boards do it without some kind of verification. I
am new to this stuff so I might be missing something obvious here.

Thanks again.
O.O.


On May 16, 5:16 am, Kolja Sulimma <ksuli...@googlemail.com> wrote:
> Hi,
>
> why would you want to use Virtex-II on a new board? They are more
> expensive than the newer parts. Check out the various Spartan-3
> variants and Virtex-5LX.
>
> You need to supply power more or less to all power pins and you
> definitely should use a board with at least 4 layers.
>
> Kolja
>

Actually we check it by eyes. You know, one designs others check! It
is a matter of experience I think.

On Fri, 16 May 2008 02:29:52 -0700 (PDT), "O. Olson"
<olson_ord@yahoo.it> wrote:

>Hi,
>
>	I need to interconnect two or four FPGAs on a PCB, and I am looking
>at the prospect of designing these boards myself. If any one has done
>this, I would be grateful if you could provide some pointers,
>especially links to websites that have this information. I would
>probably be using the Xilinx Virtex II
>
>	I don&#4294967295;t know how to start this &#4294967295; but I have a few questions. Is it
>possible for me to simulate the setup between FPGAs connected on a PCB
>board. Or is it possible for me to bread board the FPGA &#4294967295; I have not
>heard of this though. I have looked at the manual of the Virtex II,
>and there are a large numbers of pins &#4294967295; I have yet to figure out which
>pins I need to power at the minimum to get this to work. So I don&#4294967295;t
>want to start laying out a PCB Board immediately.

Here is one approach to breadboarding with multiple FPGAs, which may
allow you to prototype your system before going to your own PCB.

http://www.enterpoint.co.uk/moelbryn/overcoat.html

Since you are using the Spartan kit, this board
http://www.enterpoint.co.uk/moelbryn/raggedstone1.html
is probably the most suitable component for the above approach.

They can also supply PC104 form-factor boards stackable the same way.
http://www.enterpoint.co.uk/moelbryn/hollybush1.html

- Brian

On May 16, 6:13 am, Enes Erdin <eneser...@gmail.com> wrote:
> Actually we check it by eyes. You know, one designs others check! It
> is a matter of experience I think.

Thanks for your response Enes. So do you guys ever breadboard your
stuff =96 or it is direct on the PCB?
Thanks again,
O.O.

On 16 May=FDs, 06:01, "O. Olson" <olson_...@yahoo.it> wrote:
> On May 16, 6:13 am, Enes Erdin <eneser...@gmail.com> wrote:
>
> > Actually we check it by eyes. You know, one designs others check! It
> > is a matter of experience I think.
>
> Thanks for your response Enes. So do you guys ever breadboard your
> stuff - or it is direct on the PCB?
> Thanks again,
> O.O.

Hi,

Although I am not so much experienced about these topics in my answer
I am referring to -experienced- people who designed boards in the
past. Also I must say that I have never been in a design which uses
multiple FPGA's but we designed FPGA+Microcontroller boards. As I
guess they are more or less the same thing.

We directly produce the PCB and correct the errors in the next
revisions. Besides power issues (misconnections) there are -I think-
more important topics such as using the IO standards. Misconnections
in the power pins can be corrected by examining the design multiple
times. For example by grouping the power pins in the netlist you can
easily route them without error. But if you do not specify your
standards before PCB design you can get stuck easily. Only a small
example, if you try to use _CC_ pins as output in LVDS -I am referring
to Virtex4- you certainly get into trouble but they work perfectly if
you do not use LVDS.

Unfortuantely I don't know a software checking for these errors at a
system level.

I don't know whether you know or not these issues but I hope it helps.

On May 16, 7:47 am, Enes Erdin <eneser...@gmail.com> wrote:
> On 16 May=FDs, 06:01, "O. Olson" <olson_...@yahoo.it> wrote:
>
> > On May 16, 6:13 am, Enes Erdin <eneser...@gmail.com> wrote:
>
> > > Actually we check it by eyes. You know, one designs others check! It
> > > is a matter of experience I think.
>
> > Thanks for your response Enes. So do you guys ever breadboard your
> > stuff - or it is direct on the PCB?
> > Thanks again,
> > O.O.
>
> Hi,
>
> Although I am not so much experienced about these topics in my answer
> I am referring to -experienced- people who designed boards in the
> past. Also I must say that I have never been in a design which uses
> multiple FPGA's but we designed FPGA+Microcontroller boards. As I
> guess they are more or less the same thing.
>
> We directly produce the PCB and correct the errors in the next
> revisions. Besides power issues (misconnections) there are -I think-
> more important topics such as using the IO standards. Misconnections
> in the power pins can be corrected by examining the design multiple
> times. For example by grouping the power pins in the netlist you can
> easily route them without error. But if you do not specify your
> standards before PCB design you can get stuck easily. Only a small
> example, if you try to use _CC_ pins as output in LVDS -I am referring
> to Virtex4- you certainly get into trouble but they work perfectly if
> you do not use LVDS.
>
> Unfortuantely I don't know a software checking for these errors at a
> system level.
>
> I don't know whether you know or not these issues but I hope it helps.

Thanks Enes for your information. This is exactly my problem. I have
designed PCB Boards with only microcontrollers and some memory chips =96
but this is the first time I am doing FPGAs. So I have Zero
Experience. Also I am not aware of the standards =96 that=92s why I was
hoping for some kind of tool, before I actually get to putting it on
the PCB. I feel that this would be very difficult without a tool.

Thanks again.
O.O.

> Thanks Enes for your information. This is exactly my problem. I have
> designed PCB Boards with only microcontrollers and some memory chips =96
> but this is the first time I am doing FPGAs. So I have Zero
> Experience. Also I am not aware of the standards =96 that=92s why I was
> hoping for some kind of tool, before I actually get to putting it on
> the PCB. I feel that this would be very difficult without a tool.
>
> Thanks again.
> O.O.

I think it will be easier than you think :)

First try to define your needs than make meetings with your
colleagues. Or are you also the guy who writes codes for FPGA? If your
design is not too complex it will be easier.

Your needs are well-defined in data-sheets and also too many topics
are discussed in this group about I/O things.

I advise you to look at the pinout specifications first. Also look at
the DC and switching characteristics too. As an experience of mine, in
one of our designs we needed a 20 A rush-current for an FPGA. And
things like this...

-enes

On May 16, 8:15 am, Enes Erdin <eneser...@gmail.com> wrote:
> I think it will be easier than you think :)
>
> First try to define your needs than make meetings with your
> colleagues. Or are you also the guy who writes codes for FPGA? If your
> design is not too complex it will be easier.
>
> Your needs are well-defined in data-sheets and also too many topics
> are discussed in this group about I/O things.
>
> I advise you to look at the pinout specifications first. Also look at
> the DC and switching characteristics too. As an experience of mine, in
> one of our designs we needed a 20 A rush-current for an FPGA. And
> things like this...
>
> -enes

Dear Enes,

	I am a student and looking into the possibility of taking this up for
my thesis. So actually I don=92t have any colleagues. Yes, I would be
also writing the code for the FPGAs myself  =96 and I am going to try to
keep the design simple.

	However as I am alone, and without much experience in the area, I
would first like to get a feel of how complicated this would be. Is
there anyway I get hold of the stuff you are referring to: for e.g. I
did not expect there would be a 20 A rush-current on an PCB Board.
Also I don=92t have much experience with LVDS =96 though I know what it is
and have seen others use it. So is there some place I can dig for the
concerns that you are brining up.

Thanks again.
O.O.