Send Ethernet traffic from an FPGA

I've published a 4-steps "recipe" on how to send traffic. The experiment
should be easy to follow through.

You need:
1. Any FPGA development board, with 2 free IOs and a 20 MHz clock.
2. A PC with an Ethernet card, and the TCP-IP stack installed.
3. Optionally, a network hub or switch.
No Ethernet interface chip required.

The Verilog source code (about 150 lines) is published here
http://www.fpga4fun.com/10BASE-T0.html

I'd be happy to hear how that works.
The code has been tested in two different networks, with different FPGA
boards from different vendors.

I think the applications possible are pretty cool.
Have fun!
Jean

On Tue, 13 Jan 2004 08:08:22 GMT, "Jean Nicolle"
<j.nicolle@sbcglobal.net> wrote:

>I've published a 4-steps "recipe" on how to send traffic. The experiment
>should be easy to follow through.
>
>You need:
>1. Any FPGA development board, with 2 free IOs and a 20 MHz clock.
>2. A PC with an Ethernet card, and the TCP-IP stack installed.
>3. Optionally, a network hub or switch.
>No Ethernet interface chip required.
>
>The Verilog source code (about 150 lines) is published here
>http://www.fpga4fun.com/10BASE-T0.html
>
>I'd be happy to hear how that works.
>The code has been tested in two different networks, with different FPGA
>boards from different vendors.
>
>I think the applications possible are pretty cool.
>Have fun!
>Jean

Hi Jean,

Some suggestions:

1.  This web page http://www.fpga4fun.com/10BASE-T1.html
mentions that the Ethernet standard is "IEEE 802.3ae-2002".  That's
the 10Gbps standard!  I suggest you change this to "IEEE 802.3-2002 --
Section One".
Here is the direct URL:
http://standards.ieee.org/getieee802/download/802.3-2002_part1.pdf
Chapter 14 (10Base-T) is the relevant part of that document.

2.  There is no way your circuit will meet many of the Ethernet
electrical requirements (section 14.3 in the spec).  Whilst it may
pass data, and be of great educational value, I think you really
should have a statement on your website saying that this isn't
Ethernet compliant, otherwise newbies will think that it really is
Ethernet and start designing it into their own products.

3.  You probably do need the transformers, otherwise the section
14.3.1.1 isolation requirements of 2400V (yes, that's 2.4 kV) are a
little difficult to meet.
The 1kV common mode surge requirments in 14.3.1.2.7 (transmit) and
14.3.1.3.6 (receive) may also be difficult to meet without a
transformer.

4.  The receiver may work better with a 120ohm (or so) resistor
between the RD- and RD+ pins.  This should give the receiver a better
return loss (which is meant to be 15dB minimum, according to
14.3.1.3.4), and might improve the performance on long cables.


BTW, what error rate did you get over 100m of cable?

Regards,
Allan.

Whoa, good, that's what I needed, a guy who knows a little more than I do
about the Analog Ethernet requirements.
I'll make the necessary updates on the site.

I didn't try long cables, that probably explains it why I didn't run into
problems. Will do, and try with 120ohms resistors.
Thanks.
Jean

"Allan Herriman" <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in
message news:orb700t0u712oa3tri7b5ub9264vki9flf@4ax.com...
> On Tue, 13 Jan 2004 08:08:22 GMT, "Jean Nicolle"
> <j.nicolle@sbcglobal.net> wrote:
>
> >I've published a 4-steps "recipe" on how to send traffic. The experiment
> >should be easy to follow through.
> >
> >You need:
> >1. Any FPGA development board, with 2 free IOs and a 20 MHz clock.
> >2. A PC with an Ethernet card, and the TCP-IP stack installed.
> >3. Optionally, a network hub or switch.
> >No Ethernet interface chip required.
> >
> >The Verilog source code (about 150 lines) is published here
> >http://www.fpga4fun.com/10BASE-T0.html
> >
> >I'd be happy to hear how that works.
> >The code has been tested in two different networks, with different FPGA
> >boards from different vendors.
> >
> >I think the applications possible are pretty cool.
> >Have fun!
> >Jean
>
> Hi Jean,
>
> Some suggestions:
>
> 1.  This web page http://www.fpga4fun.com/10BASE-T1.html
> mentions that the Ethernet standard is "IEEE 802.3ae-2002".  That's
> the 10Gbps standard!  I suggest you change this to "IEEE 802.3-2002 --
> Section One".
> Here is the direct URL:
> http://standards.ieee.org/getieee802/download/802.3-2002_part1.pdf
> Chapter 14 (10Base-T) is the relevant part of that document.
>
> 2.  There is no way your circuit will meet many of the Ethernet
> electrical requirements (section 14.3 in the spec).  Whilst it may
> pass data, and be of great educational value, I think you really
> should have a statement on your website saying that this isn't
> Ethernet compliant, otherwise newbies will think that it really is
> Ethernet and start designing it into their own products.
>
> 3.  You probably do need the transformers, otherwise the section
> 14.3.1.1 isolation requirements of 2400V (yes, that's 2.4 kV) are a
> little difficult to meet.
> The 1kV common mode surge requirments in 14.3.1.2.7 (transmit) and
> 14.3.1.3.6 (receive) may also be difficult to meet without a
> transformer.
>
> 4.  The receiver may work better with a 120ohm (or so) resistor
> between the RD- and RD+ pins.  This should give the receiver a better
> return loss (which is meant to be 15dB minimum, according to
> 14.3.1.3.4), and might improve the performance on long cables.
>
>
> BTW, what error rate did you get over 100m of cable?
>
> Regards,
> Allan.

Allan, did you get my email yesterday? I sent you a few screenshots.

Anyway:
1. is fixed.

2. and 3.
Looks like the way to meet the spec is to buy an isolation transformer and
follow the apps notes, a good source seems to be http://www.pulseeng.com/,
so it should be just a matter to buy these.

4., I did more experiments with a longer (30m) cable, and the results are
surprisingly good. Reflection from a terminated cable (connected to an
Ethernet switch) are low, even when driving directly from the FPGA. Putting
50ohms or 100ohms series resistors doesn't have much influence besides
attenuating the incident signal.
In all cases, I did not seem to experience any packet drops.

Good luck.
Jean


"Jean Nicolle" <j.nicolle@sbcglobal.net> wrote in message
news:BJWMb.9463$aX2.9427@newssvr27.news.prodigy.com...
> Whoa, good, that's what I needed, a guy who knows a little more than I do
> about the Analog Ethernet requirements.
> I'll make the necessary updates on the site.
>
> I didn't try long cables, that probably explains it why I didn't run into
> problems. Will do, and try with 120ohms resistors.
> Thanks.
> Jean
>
> "Allan Herriman" <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in
> message news:orb700t0u712oa3tri7b5ub9264vki9flf@4ax.com...
> > On Tue, 13 Jan 2004 08:08:22 GMT, "Jean Nicolle"
> > <j.nicolle@sbcglobal.net> wrote:
> >
> > >I've published a 4-steps "recipe" on how to send traffic. The
experiment
> > >should be easy to follow through.
> > >
> > >You need:
> > >1. Any FPGA development board, with 2 free IOs and a 20 MHz clock.
> > >2. A PC with an Ethernet card, and the TCP-IP stack installed.
> > >3. Optionally, a network hub or switch.
> > >No Ethernet interface chip required.
> > >
> > >The Verilog source code (about 150 lines) is published here
> > >http://www.fpga4fun.com/10BASE-T0.html
> > >
> > >I'd be happy to hear how that works.
> > >The code has been tested in two different networks, with different FPGA
> > >boards from different vendors.
> > >
> > >I think the applications possible are pretty cool.
> > >Have fun!
> > >Jean
> >
> > Hi Jean,
> >
> > Some suggestions:
> >
> > 1.  This web page http://www.fpga4fun.com/10BASE-T1.html
> > mentions that the Ethernet standard is "IEEE 802.3ae-2002".  That's
> > the 10Gbps standard!  I suggest you change this to "IEEE 802.3-2002 --
> > Section One".
> > Here is the direct URL:
> > http://standards.ieee.org/getieee802/download/802.3-2002_part1.pdf
> > Chapter 14 (10Base-T) is the relevant part of that document.
> >
> > 2.  There is no way your circuit will meet many of the Ethernet
> > electrical requirements (section 14.3 in the spec).  Whilst it may
> > pass data, and be of great educational value, I think you really
> > should have a statement on your website saying that this isn't
> > Ethernet compliant, otherwise newbies will think that it really is
> > Ethernet and start designing it into their own products.
> >
> > 3.  You probably do need the transformers, otherwise the section
> > 14.3.1.1 isolation requirements of 2400V (yes, that's 2.4 kV) are a
> > little difficult to meet.
> > The 1kV common mode surge requirments in 14.3.1.2.7 (transmit) and
> > 14.3.1.3.6 (receive) may also be difficult to meet without a
> > transformer.
> >
> > 4.  The receiver may work better with a 120ohm (or so) resistor
> > between the RD- and RD+ pins.  This should give the receiver a better
> > return loss (which is meant to be 15dB minimum, according to
> > 14.3.1.3.4), and might improve the performance on long cables.
> >
> >
> > BTW, what error rate did you get over 100m of cable?
> >
> > Regards,
> > Allan.
>
>

Jean Nicolle <j.nicolle@sbcglobal.net> wrote:
: Allan, did you get my email yesterday? I sent you a few screenshots.

: Anyway:
: 1. is fixed.

: 2. and 3.
: Looks like the way to meet the spec is to buy an isolation transformer and
: follow the apps notes, a good source seems to be http://www.pulseeng.com/,
: so it should be just a matter to buy these.

An old 10 MBit card might be a good source for the transformer..

...

: > > 4.  The receiver may work better with a 120ohm (or so) resistor
...

Please don't fullquote. It only fills up the archive with redundancy...

Bye

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

On Wed, 14 Jan 2004 18:50:37 GMT, "Jean Nicolle"
<j.nicolle@sbcglobal.net> wrote:

>Allan, did you get my email yesterday? I sent you a few screenshots.

Oops, sorry, forgot to respond.

>Anyway:
>1. is fixed.
>
>2. and 3.
>Looks like the way to meet the spec is to buy an isolation transformer and
>follow the apps notes, a good source seems to be http://www.pulseeng.com/,
>so it should be just a matter to buy these.

Also try Prem, Pico, Midcom, Halo, Gowanda, etc.  Note that these
transformers will be designed to work with different PHYs, and each
PHY will require a different turns ratio (which determines the
impedance ratio, and is sometimes not 1:1) and can tolerate a
different amount of leakage inductance.  
This means that pulling a transformer out of any old 10Base-T Ethernet
card isn't guaranteed to give good results with your design.  (Of
course, you can get the part number of the PHY from the Ethernet card
and look up its specs to find out what the transformer is like.)

If your design already works with a direct connection to the cable, I
suggest starting with a 1:1 transformer.

>4., I did more experiments with a longer (30m) cable, and the results are
>surprisingly good. Reflection from a terminated cable (connected to an
>Ethernet switch) are low, even when driving directly from the FPGA. Putting
>50ohms or 100ohms series resistors doesn't have much influence besides
>attenuating the incident signal.
>In all cases, I did not seem to experience any packet drops.

Ummm, those reflections are a function of the terminating impedance
(i.e. the Ethernet switch), so you'd expect them to be low.
The comment in my earlier post about terminating impedance was to do
with the input of your circuit, which affects the reflections of the
signal coming from the other end.  A resistor across RD-/RD+ should
make this better.

Regards,
Allan.

Sounds reasonable.
Jean

"Uwe Bonnes" <bon@elektron.ikp.physik.tu-darmstadt.de> wrote in message
news:bu43s0$vcl$1@news.tu-darmstadt.de...
> Jean Nicolle <j.nicolle@sbcglobal.net> wrote:
> : Allan, did you get my email yesterday? I sent you a few screenshots.
>
> : Anyway:
> : 1. is fixed.
>
> : 2. and 3.
> : Looks like the way to meet the spec is to buy an isolation transformer
and
> : follow the apps notes, a good source seems to be
http://www.pulseeng.com/,
> : so it should be just a matter to buy these.
>
> An old 10 MBit card might be a good source for the transformer..
>
> ...
>
> : > > 4.  The receiver may work better with a 120ohm (or so) resistor
> ...
>
> Please don't fullquote. It only fills up the archive with redundancy...
>
> Bye
>
> -- 
> Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de
>
> Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
> --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

Yes, there are lots of manufacturers of magnetics.

I found this page

http://www.interfacebus.com/inductors_transformers.html



About the reflection, since this particular experiment is an emitter only,
I'm relying on the other end device (an Ethernet switch) to do proper
termination (which it does, according to my measurements).

Once I work further on the receiver part, I certainly need to pay attention
to terminating the lines i.e. putting a resistor across the pair.
Thanks.
Jean

(and I remembered not to fullquote this time).

Jean Nicolle wrote:

(snip)

> About the reflection, since this particular experiment is an emitter only,
> I'm relying on the other end device (an Ethernet switch) to do proper
> termination (which it does, according to my measurements).

> Once I work further on the receiver part, I certainly need to pay attention
> to terminating the lines i.e. putting a resistor across the pair.

It is still best to terminate both directions, but it will generally
work if you terminate one end, for protocols that only send one
direction on each pair.

As you say, if the receiver is terminated, there won't be a reflection. 
  It the transmitter is properly terminated, the reflection from the
receiver will be absorbed at that point, and won't cause problems
(most of the time).

When you get to gigabit, using both directions on each pair at the
same time, proper termination of both ends is much more important.

Termination at both ends for unidirectional systems allows a
tolerance for mismatch.  If 10baseT is terminated at 120 ohms,
then using cable between 100 ohms and 150 ohms will result in
at most about 20% reflection.  At most about 20% of that,
or 4% of the original will then reflect back again from the
other end.

-- glen

That makes sense.
Terminating the receiver is just a matter of putting a resistor across the
wire pair.

Now, the question is, how to terminate the transmitter?

If I assume cat5 cables (100ohms differential impedance?), my first thought
is to put two 50ohms series resistors on the transmitter side. The downside
is, it is going to cut in half the incident wave.
Any better way?
Jean