Low-end FPGA mezzanine standard

[Theo Markettos]

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

 

[Uwe Bonnes]

Theo Markettos <theom+news@chiark.greenend.org.uk> wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

store.hackaday.com/products/arduino-compatible-fpga-shield ?

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

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

 

[Theo Markettos]

Uwe Bonnes <bon@hertz.ikp.physik.tu-darmstadt.de> wrote:
> store.hackaday.com/products/arduino-compatible-fpga-shield ?

Thanks. I found that earlier, but it's the wrong direction. I already have
an FPGA (a Cyclone IV E EP4CE22, with no transceivers), I want to connect it
via a high-ish bandwidth link to the outside world (via USB 2, 100M
Ethernet, whatever), but I don't want to commit to a protocol, I just want
to add a header and use existing modules.

The above seems to be intended to add an FPGA to an Arduino. As the Spartan
6 LX doesn't have any high speed transceivers, it seem doesn't add anything
to the FPGA I already have.

Theo

 

[rickman]

On 11/26/2014 7:12 PM, Theo Markettos wrote:

Uwe Bonnes <bon@hertz.ikp.physik.tu-darmstadt.de> wrote:
store.hackaday.com/products/arduino-compatible-fpga-shield ?

Thanks. I found that earlier, but it's the wrong direction. I already have
an FPGA (a Cyclone IV E EP4CE22, with no transceivers), I want to connect it
via a high-ish bandwidth link to the outside world (via USB 2, 100M
Ethernet, whatever), but I don't want to commit to a protocol, I just want
to add a header and use existing modules.

The above seems to be intended to add an FPGA to an Arduino. As the Spartan
6 LX doesn't have any high speed transceivers, it seem doesn't add anything
to the FPGA I already have.

When I looked I found a number of modules that would provide external
interfaces having nothing to do with Arduino. Check again and nose
around a bit.

--

Rick

 

[Alexander Kane]

I don't have any suggestions but would be very interested if you find anything along those lines. Please post anything you do find.

 

[Theo Markettos]

Alexander Kane <ajpkane@gmail.com> wrote:

I don't have any suggestions but would be very interested if you find
anything along those lines. Please post anything you do find.

So far I'm leaning toward Arduino, but using some of the non-Atmega boards
that are a bit quicker and pretending that my board is an Arduino shield
(rather than a CPU). For instance:

Intel Galileo release 2: i386 Quark processor that can run Debian (with
hackery, Intel have a critical bug on the LOCKXCHG instruction), has PCIe,
ethernet, on the rel 2 board there's now 12 native GPIOs (up from a derisory
2 on the rel 1 board that I have). i386 compatibility may be useful for my
application, but this is a bit underpowered. I don't know if there's a way
to do high speed parallel input though.

BeagleBone: there's a pair of cacheless single-cycle 200MHz Programmable
Realtime Unit CPUs attached to some GPIOs, that might be enough to suck in
data into the main CPU that has Ethernet, USB, etc. Programming the PRUs
looks a bit fiddly. Not Arduino pinout.

Arduino Tre: essentially a Beaglebone with an Arduino integrated. This puts
a 16MHz ATMega 32u4 on the other end of the Arduino pins - so maximum
16MHz x n bits input, assuming it can be convinced to do one word per cycle
(which I'm not sure it can). I don't think the Arduino pins are accessible
from the PRUs, though I haven't found a pinout (it doesn't exist yet).

Arduino Yun: same idea as the Tre, but with an Atheros AR9331 wifi
controller. Ignoring the wifi bit, it's the same problem - all the external
IO goes via the slow ATMega.

All of these are higher cost than the average Arduino shield, and
essentially mean committing to a board with a given pinout (since in reality
only Arduino pins XYZ have the necessary properties). They also mean all
going through a 'full fat' OS to get the high speed I/O.

Theo

 

[Theo Markettos]

mnentwig <24789@embeddedrelated> wrote:
> "PMOD" and Arduino-style wings are the two "standards" I know of.

Interesting, I wasn't aware of PMOD. That's the kind of thing I'm after,
but it seems to be limited in both pinout and speed. For instance, there's
a 100M ethernet but you have to talk to it by SPI. Likewise the only USB is
a UART. So a 'parallel PMOD' is roughly what I'm looking for.

Theo

 

[mnentwig]

"PMOD" and Arduino-style wings are the two "standards" I know of.

---------------------------------------
Posted through http://www.FPGARelated.com

 

[vanepp]

Anyone know if there's a standard(ish) for simple mezzanine cards fo
FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, whic
is
simple and low pin count, but everything is designed to talk to a dum
slow
Atmega (which usually means putting another Atmega on the mezzanine car
and
talking via SPI). Or there's Raspberry Pi, but again it's assumes yo
have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scal
system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA.
For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offloa
is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of
community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

http://enterpoint.co.uk/ has both 10/100 and 10/100/1000 Phys alon
with other
fpga interface stuff in their standard pinout. As well I know of waveshar
(also
available from various folks on ebay) who have a cheap 10/100 phy

http://www.wvshare.com/product/DP83848-Ethernet-Board.htm

Peter Van Epp



---------------------------------------
Posted through http://www.FPGARelated.com

 

[Tomas D.]

Hello Theo,

"Theo Markettos" <theom+news@chiark.greenend.org.uk> wrote in message
news:nQx*EJyhv@news.chiark.greenend.org.uk...

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which
is
simple and low pin count, but everything is designed to talk to a dumb
slow
Atmega (which usually means putting another Atmega on the mezzanine card
and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you
have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA.
For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload
is
a useful task), just drinking it through an SPI straw is not.

You can find really bare and cheap ones:
DE0-nano:
http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=165&No=593
or DE0:
http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=165&No=364
If you want something more advanced, but with reasonable connectors, then
have a look at DE1-SoC:
http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=165&No=836

I think all the development kits that come with the HSMC connector, also
have a very small board with like 20 LEDs and 40 IO pins. The one on the
left:
http://kamami.com/published/publicdata/BTC10/attachments/SC/products_pictures/m_terasic_p0057.jpg

 

[Antti]

On Wednesday, 26 November 2014 20:01:18 UTC+1, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

we are working on it, we really are:

https://hackaday.io/project/3443-open-source-hw-xilinx-zynq7000-system-on-module

this is only the tip of the iceberg the project will be launhced on indiegogo latest next week, with promo perks at 39EUR (inclusive shipping)

there are at least 3 more different form factors coming, some much more interesting in the sense of "mezzanine".

OzOM - A features

* 2x ARM cortex A9
* 32MByte linear NOR flash
* 1 pmod slot, 4 MIO and 4 FPGA
* 1 i2c slot (pmod compat) 4 MIO
* 50 pin header, both edges are "pmod compatible"
* SD Card sockets, supporting:
** SD/SDXC, failsafe primary boot
** Electric Imp wifi cloud
** Toschiba FlashAir - iSDIO wifi
** AK2000 based WiFi cards with built in linux (user accessible!!)
* microSD - secondary boot, flash media if using SDIO cards in other slot
* MSP430 as reset and "button" controller
* LED's
* uni-taster: reset or reconfigure or clear config or user button
* CC2564 based BT/BLE either TiWi-uB2 or CC2564MODN
** onboard antenna or U.fl connector
* USB possible if ULPI phy on baseboard
* ethernet 100Mbit possible with RMII phy
* ethernet 10Mbit possible with "phyless - phy"

there are some more features coming in REV 2, the above list was for REV 1 boards that we have at our desk and use to evaluate the design and improve it before pilot series production.

 

[Theo Markettos]

Antti <antti.lukats@gmail.com> wrote:

On Wednesday, 26 November 2014 20:01:18 UTC+1, Theo Markettos wrote:
Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

we are working on it, we really are:

https://hackaday.io/project/3443-open-source-hw-xilinx-zynq7000-system-on-module

To be clear, I'm actually looking for the other way around. I already have an FPGA,
I want to add some I/O via mezzanine cards. Do you plan to make any addon
cards that fit into your board?

(adding an FPGA plus its own I/O is a way to go, I suppose, but it starts getting
complicated)

Theo

 

[Antti]

On Wednesday, 26 November 2014 20:01:18 UTC+1, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

Hi Theo,

yes, well I have done some standards and produced some addonboards, unfortunately with not so much widespread success.

the need is there, and the existing standards do not covert the needs.

I may have something in the "sleeves" too early to talk, but I can say it ends for me multi-decade search and hunt. Search is over.

Sorry just a little bit too early to talk in public.

br
Antti

 

[Tom Gardner]

On 26/11/14 19:01, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

The nice thing about standards is that there are so many
to choose from

Have a look at
http://papilio.cc/
http://www.ztex.de/usb-fpga-1/
http://www.sioi.com.au/shop/product_info.php/products_id/47
http://www.element14.com/community/docs/DOC-69129
http://www.opalkelly.com/products/xem6001/
http://zedboard.org/products
but notice that many of the cheaper ones don't have enough ground lines near the
signal lines.

 

[mnentwig]

mnentwig <24789@embeddedrelated> wrote:
"PMOD" and Arduino-style wings are the two "standards" I know of.


Interesting, I wasn't aware of PMOD. That's the kind of thing I'm after,
but it seems to be limited in both pinout and speed. For instance
there's
a 100M ethernet but you have to talk to it by SPI. Likewise the only US
is
a UART. So a 'parallel PMOD' is roughly what I'm looking for.

Theo

Hi,

you could have a look at this:
http://retrocade.gadgetfactory.net/index.php?n=Main.Hardware

The 2nd picture shows the Papilio Pro board (with Spartan 6 LX9 FPGA), an
there are three connectors with 16 GPIOs each, plus power. Two ar
side-by-side at the bottom.
The physical placement of the three connectors is standardized (sort of)
The board in the top picture, with the LCD, makes use of that.
Three are a bunch of (even) smaller FPGA boards from the same vendor, and
XC6LX45 here:

http://pipistrello.saanlima.com/index.php?title=Welcome_to_Pipistrello
Using all three connectors provides 48 GPIOs to a stacked board.

This is meant for the hobbyist market using two-layer boards. The whol
thing is a hack - takes some practice to assemble the boards withou
bending pins - but works well enough.

---------------------------------------
Posted through http://www.FPGARelated.com

 

On Wednesday, November 26, 2014 1:01:18 PM UTC-6, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

If one wants something beyond Arduino and Pmod connections, one could use USB 3.0 extension cabling as the basis for hackable interconnect: Use the USB 2.0 wires for power, ground and some simple standard interface (I2C, SPI, UART, CAN, etc). That leaves the two USB 3.0 pairs for the serial interface of your own devising. With a microprocessor and/or FPGA on each end it's your choice.

 

[Antti]

On Saturday, 29 November 2014 16:58:04 UTC+1, jim.bra...@ieee.org wrote:

On Wednesday, November 26, 2014 1:01:18 PM UTC-6, Theo Markettos wrote:
Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

If one wants something beyond Arduino and Pmod connections, one could use USB 3.0 extension cabling as the basis for hackable interconnect: Use the USB 2.0 wires for power, ground and some simple standard interface (I2C, SPI, UART, CAN, etc). That leaves the two USB 3.0 pairs for the serial interface of your own devising. With a microprocessor and/or FPGA on each end it's your choice.

USB connectors have been used and missued already by some projects

for the most hacking experience there is nothing but 100 mil headers

Antti
http:/igg.me/at/zynq

 

[Antti]

On Wednesday, 26 November 2014 20:01:18 UTC+1, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

yes and IDEA is born, will be public soon -
[prelim spec deleted here, sorry]


Antti wishes merry Christmas

 

On Saturday, November 29, 2014 11:27:47 AM UTC-6, Antti wrote:

On Saturday, 29 November 2014 16:58:04 UTC+1, jim.bra...@ieee.org wrote:
On Wednesday, November 26, 2014 1:01:18 PM UTC-6, Theo Markettos wrote:
Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

If one wants something beyond Arduino and Pmod connections, one could use USB 3.0 extension cabling as the basis for hackable interconnect: Use the USB 2.0 wires for power, ground and some simple standard interface (I2C, SPI, UART, CAN, etc). That leaves the two USB 3.0 pairs for the serial interface of your own devising. With a microprocessor and/or FPGA on each end it's your choice.

USB connectors have been used and missued already by some projects

for the most hacking experience there is nothing but 100 mil headers

Antti
http:/igg.me/at/zynq

Have nothing against 0.1" headers except their size and the inflexibility of where the GND and VCC pins are located. One could go to 2mm headers, they are less available and too small for my fingers.

However, it should be possible to make GND available for, say, any of the odd pins and VCC available for any of the even pins. This would allow maximum utilization of the 0.1" spaced pins/holes, giving upwards of twice the density of Pmod connections. Can think of several ways to allow the GND and VCC connections, probably the cheapest and most compact is "solder bridges": small copper circles with a open area down the middle of the circle.

 

On Wednesday, November 26, 2014 11:01:18 AM UTC-8, Theo Markettos wrote:

Anyone know if there's a standard(ish) for simple mezzanine cards for FPGA
boards?

I know about things like FMC and HSMC which are very 'high end' - multi
gigabit transceivers, expensive connectors. There's also Arduino, which is
simple and low pin count, but everything is designed to talk to a dumb slow
Atmega (which usually means putting another Atmega on the mezzanine card and
talking via SPI). Or there's Raspberry Pi, but again it's assumes you have
slow I/O and things like Ethernet and USB already exist on the CPU board.

Is there anything between the two? Something like an Arduino-scale system
but with a $10 FPGA in mind rather than an 8 bit micro or a $1000 FPGA. For
instance, an 100M Ethernet PHY which is just the phy rather than a
memory-mapped MAC, and so just presents an RMII or SMII interface. Or a
USB2 ULPI PHY. Having a microcontroller on the board is OK (USB offload is
a useful task), just drinking it through an SPI straw is not.

I found:
http://www.wvshare.com/column/Accessory_Boards.htm?1
which seems to be cheap boards all over ebay that are rather Arduino-like
while intended for FPGAs, but there doesn't seem to be much of a community
around them (in other words, they might disappear tomorrow).

Any other ideas?

Thanks
Theo

Check out the Bugblat devices that support some of the open hardware platforms based on Lattice FPGAs.

http://www.bugblat.com/products/pif/index.html
http://www.bugblat.com/products/fino/index.html