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Really nice design! Impressive routing, I was surprised you were able to fit two DDR chips on there as well. It's still too bad that all the tooling for this i

Really nice design! Impressive routing, I was surprised you were able to fit two DDR chips on there as well. It's still too bad that all the tooling for this is closed source (Altium, Xilinx ISE / Vivado, with the latter being far more offensive). But the Spartan 6 is a really nice chip otherwise. It seems like the target application is compute acceleration. Do you have any particular applications in mind?

jjoonathan 11y ago
Another possible application: talking to high speed serial busses. This isn't just a Spartan 6, it's a Spartan 6 XCblahblahT. Usually when you see cheap Spartan 6 boards they use the non-transceiver version to cut costs without mentioning that it cuts one of the killer features of the chip! This one is the real deal. You still have to use ISE (not even Vivado; they locked the Spartan 6s out of Vivado) but it's still nice. EDIT: they may have brought all the transceivers out to PCIe; I'd have to look closer to tell for sure.
- opello 11y ago
  This is MiniPCIe which would only have a x1 connection to the edge fingers, which means only 4 GTP connections would be needed (and the XC6SLX100T has 8 IIRC).
aceperry 11y ago
This. Although I think Altium is the more offensive toolset. The real fly in the ointment for open source hardware is the proprietary tooling.
- TD-Linux 11y ago
  I've since moved on to KiCAD and been pretty happy with it. Something like this board would still be near difficult to impossible, though, as impedance matching for the DDR lines doesn't really exist in KiCAD. I also ordered a few ICEsticks to play with the new icestorm open source toolchain. That FPGA is in no way comparable to a Spartan 6, though.
  - dfox 11y ago
    New KiCAD versions (from bzr) have push and shove interactive router which also can do length matching and differential pairs, although the whole thing is far from complete and stable but it is usable (for example, the "push and shove" part does not work when routing diff pairs and when you move move mouse too fast in plain track routing mode it just crashes). One problem with these new features is that they are somehow linked to new implementation of pcbnew's canvas which also implies somewhat different UI behavior (more windows-like, with selection of individual PCB elements and so on), which I generally don't like that much. Anyhow I recently used current kicad from bzr for somewhat non-trivial board (smallish FPGA in TQFP, ARM MCU, some analog RF, few LVDS lines).
- michaelt 11y ago
  Altium have recently released 'circuitmaker' which is basically a $0 version of Altium, for open hardware. I guess it's meant to compete with Eagle, which a lot of open hardware projects use. It's still closed source (like Eagle). And it's Windows-only. And currently there's a DirectX conflict with VirtualBox so you can't use it there (reportedly it works in other VMs). But it's cheaper than paying $9000-a-seat-plus-$1000-a-year-maintainance for commercial Altium.
mng2 11y ago
It should be mentioned that the '100T device pictured actually requires the full paid version of ISE. The free-as-in-beer ISE Webpack only supports up to the '75T. Thankfully Xilinx implemented compatible packages through the device family, so lower devices are a drop-in replacement (mostly). Maybe one day we'll have a Free toolchain, but FPGA tools are much closer to chip design tools than to compilers, and the space is fraught with patent concerns. However I did read on Deep Chip that some fundamental synthesis patents have been invalidated, which might open up some breathing room.
- mindcrime 11y ago
  Supposedly, a lot of key FPGA patents are set to expire Real Soon Now, or just did, or something along those lines. I'm holding out hope that we'll have a true Open Source FPGA environment sooner or later, but it sure is taking it's time... :-(
  - Tomte 11y ago
    Are patents really what's blocking it? I only have a passing understanding of the FPGA world, but I thought that everything in that space in shrouded in trade secrets. Do patent claim descriptions really have enough detail to help you produce a working bitstream?
    - wtallis 11y ago
      Patent threats don't really hinder community reverse engineering efforts, but they do discourage the major vendors from being open-source friendly, because nobody wants to open up their tech only to get sued over the details you just disclosed.
    - sliverstorm 11y ago
      That's a key point, Altera and Xilinx may well have decided to keep some of their inventions secret, banking on being able to keep them secret, In which case a patent may do them little good. And there is no 7-year date of expiry on secrets.
    - 11y ago
masta 11y ago
I was a bit surprised to see an asymmetric stackup, many board-houses will complain about that. It can also become a problem during assembly, because the different heat distributions can cause the board to warp. Neither the schematics nor the layout would have passed a proper review. On the other hand, thanks for providing the data to the public, it is an interesting project either way.

jjoonathan 11y ago

Another possible application: talking to high speed serial busses. This isn't just a Spartan 6, it's a Spartan 6 XCblahblahT. Usually when you see cheap Spartan 6 boards they use the non-transceiver version to cut costs without mentioning that it cuts one of the killer features of the chip! This one is the real deal. You still have to use ISE (not even Vivado; they locked the Spartan 6s out of Vivado) but it's still nice. EDIT: they may have brought all the transceivers out to PCIe; I'd have to look closer to tell for sure.

opello 11y ago
This is MiniPCIe which would only have a x1 connection to the edge fingers, which means only 4 GTP connections would be needed (and the XC6SLX100T has 8 IIRC).

aceperry 11y ago

This. Although I think Altium is the more offensive toolset. The real fly in the ointment for open source hardware is the proprietary tooling.

TD-Linux 11y ago
I've since moved on to KiCAD and been pretty happy with it. Something like this board would still be near difficult to impossible, though, as impedance matching for the DDR lines doesn't really exist in KiCAD. I also ordered a few ICEsticks to play with the new icestorm open source toolchain. That FPGA is in no way comparable to a Spartan 6, though.
- dfox 11y ago
  New KiCAD versions (from bzr) have push and shove interactive router which also can do length matching and differential pairs, although the whole thing is far from complete and stable but it is usable (for example, the "push and shove" part does not work when routing diff pairs and when you move move mouse too fast in plain track routing mode it just crashes). One problem with these new features is that they are somehow linked to new implementation of pcbnew's canvas which also implies somewhat different UI behavior (more windows-like, with selection of individual PCB elements and so on), which I generally don't like that much. Anyhow I recently used current kicad from bzr for somewhat non-trivial board (smallish FPGA in TQFP, ARM MCU, some analog RF, few LVDS lines).
michaelt 11y ago
Altium have recently released 'circuitmaker' which is basically a $0 version of Altium, for open hardware. I guess it's meant to compete with Eagle, which a lot of open hardware projects use. It's still closed source (like Eagle). And it's Windows-only. And currently there's a DirectX conflict with VirtualBox so you can't use it there (reportedly it works in other VMs). But it's cheaper than paying $9000-a-seat-plus-$1000-a-year-maintainance for commercial Altium.

mng2 11y ago

It should be mentioned that the '100T device pictured actually requires the full paid version of ISE. The free-as-in-beer ISE Webpack only supports up to the '75T. Thankfully Xilinx implemented compatible packages through the device family, so lower devices are a drop-in replacement (mostly). Maybe one day we'll have a Free toolchain, but FPGA tools are much closer to chip design tools than to compilers, and the space is fraught with patent concerns. However I did read on Deep Chip that some fundamental synthesis patents have been invalidated, which might open up some breathing room.

mindcrime 11y ago
Supposedly, a lot of key FPGA patents are set to expire Real Soon Now, or just did, or something along those lines. I'm holding out hope that we'll have a true Open Source FPGA environment sooner or later, but it sure is taking it's time... :-(
- Tomte 11y ago
  Are patents really what's blocking it? I only have a passing understanding of the FPGA world, but I thought that everything in that space in shrouded in trade secrets. Do patent claim descriptions really have enough detail to help you produce a working bitstream?
  - wtallis 11y ago
    Patent threats don't really hinder community reverse engineering efforts, but they do discourage the major vendors from being open-source friendly, because nobody wants to open up their tech only to get sued over the details you just disclosed.
  - sliverstorm 11y ago
    That's a key point, Altera and Xilinx may well have decided to keep some of their inventions secret, banking on being able to keep them secret, In which case a patent may do them little good. And there is no 7-year date of expiry on secrets.
  - 11y ago

masta 11y ago

I was a bit surprised to see an asymmetric stackup, many board-houses will complain about that. It can also become a problem during assembly, because the different heat distributions can cause the board to warp. Neither the schematics nor the layout would have passed a proper review. On the other hand, thanks for providing the data to the public, it is an interesting project either way.