Minimalist Spartan6-LX150 board

[eldentyrell]

Updates: see this post and this one too.



Hi folks.  I've built a mining board for myself and I'm trying to
gauge interest to see if it's worth putting in a large PCB order and
reselling them (fully assembled).

Attached are photos of the version 7.0 board.  If all goes well I'll
be selling the version 8.0 boards, taking orders around 3-Oct and
shipping around 10-Oct.  The boards will sell for $250 in the basic
configuration, which is:

  - The board (85mm x 65mm)
  - Spartan6 LX150-2
  - Bypass capacitors
  - Xilinx JTAG connector
  - 10Mhz clock crystal
  - Mounting holes for a standard Northbridge heatsink (two different
    hole diameters; rotate the sink 90 degrees to change width).
  - High-current Molex connector (see below)

The black 20-pin right-angle connector shown in the photo will not be
on the final board, and some of the unsoldered pads will change or go
away.

The board is designed to take power from a backplane (see photo) using
a high-current Molex connector.  This connector is the same kind used
on ATX motherboards, but has a different pin count and keying so you
can't plug it in by accident (!).  The Molex connector carries 1.2V
(high current) and 3.3V power, ground, one I/O pin, and all the JTAG
wires.

The backplane (sold separately for $160) has slots for six boards and
includes a SATA power connector and 48W power supply.  The JTAG
chain enters via the backplane and snakes through all the boards, so
no extra cables are required.  Airflow is meant to come in through the
side.

Extra options (includes parts+assembly):

  - $15 for 12W power supply and SATA connector so you don't need the
    backplane.

  - $5 for a 20-pin connector carrying DONE, INIT_B, PROGRAM_B, ground,
    and 14 general-purpose I/O pins.  Or you can always solder this yourself later.
    This connector means that if you decide to stop mining, you
    can still use the board for plenty of other FPGA-related projects.

  - $20 to upgrade from a Spartan6 -2 to a -3, although I'm not convinced
    this is worth it.  Parts are often "graded" into the -2 bin for reasons that
    don't affect mining performance (I/Os and DSP slices).

Payment will be only via bitcoin; my margins on this are so slim that
it only takes one stolen-credit-card order to wipe out whatever
meager profit I'll make on two dozen boards.  Escrow is fine as long
as the buyer pays; I'm still trying to figure out which service(s) to
use.

Anyways, please let me know -- zero commitment -- how many boards you
would be likely to order at the pricing and availability dates above.
That will help me figure out if I should place a large PCB order or just get
enough for myself.

Thanks!

[1713433066]

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[1713433066]

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[1713433066]

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[thirdlight]

Interesting - what H/s are you getting?

[eldentyrell]

Interesting - what H/s are you getting?

The same as anybody else using a Spartan6-LX150.  There's nothing special about this board except for the backplane option and the fact that it costs a whole lot less than the boards sold by Digilent, etc.

I currently mine with my own HDL code -- which is not performing very well yet (!).  I have deliberately not looked at or downloaded fpgaminer's code in order to avoid being the target of accusations.

If somebody posts a bitstream for an LX150-2 with an 10Mhz clock input on pin B10 (IOSTANDARD=LVCMOS33), all other communication is over JTAG, I will be happy to try it out and post results here within a day or two.  Please include the timing report (twr) and map report (mrp).

In terms of testing the hardware itself, I have run a single "lane" of my own hashing code at 320mhz (which is the BRAM speed limit on a -3 and out-of-spec for a -2) and have run current draw tests (fill the chip with shift registers, crank up the clock speed) up to 10A using the backplane power supply.  Everything worked perfectly, no errors.

(FWIW, though, there's absolutely no hope of PAR finishing with the whole chip full of lanes at 320mhz, and I have to waste an ungodly quantity of registers on pipelining.  The point is that the power supply is stable and reliable at high clock speeds and high current draw, not that you'd actually want to do mining this way (you don't).)

[rph]

The ztex Verilog is GPL and can be easily modified to reach ~150MH/s in -3, with 2 cycles per SHA256 stage,
if you'd like to switch to that. See the discussion here https://bitcointalk.org/index.php?topic=40047.0

The through-hole bypass caps are just strange (WTF, don't those interfere with the heatsink?).
The price looks very competitive though.

-rph

[sadpandatech]

The ztex Verilog is GPL and can be easily modified to reach ~150MH/s in -3, with 2 cycles per SHA256 stage,
if you'd like to switch to that. See the discussion here https://bitcointalk.org/index.php?topic=40047.0

The through-hole bypass caps are just strange (WTF, don't those interfere with the heatsink?).
The price is very competitive though. Well done.

-rph

I was thinking the same thing about the heatsink on first sight. Only thing that makes sense is if the chip side of the heatsink has a smaller footprint than the outer edge we can see.

[eldentyrell]

The through-hole bypass caps are just strange

Keeps the cost down and yield up.  Everything except the BGA chip is assembled by hand, and hand-soldering SMT capacitors is notoriously unreliable/time-consuming.

(WTF, don't those interfere with the heatsink?)

The caps actually lay down on their sides (I took the first picture before doing this).  You also have to put a small 14mmx14mmx3mm "mini heatsink" (basically just a block of copper or aluminum) between the chip and the huge northbridge sink; I'll include this with any boards that are ordered since I'm sure I can get them for under a dollar.  Pressure from the springs on the northbridge keeps it in place, but you can always add a drop of tacky thermal compound if you're paranoid.

[Silverpike]

This is outstanding, I love it.  The power connector configuration is really great, I love the mini-backplane.

This is the nicest and most compact Spartan-6 board I have yet seen.  Great job!

[fivebells]

Will it be possible for the end-user to reprogram this thing?  Might be fun.

[Dexter770221]

48W from SATA connector thats over 4A of current from 12V rail. Specs are 1.5A from this rail. You may SMELL trouble if you populate all slots...

[Dargo]

I'm trying to get a ballpark estimate of the hash/s and wattage here. Each board consumes 12 watts (or less), and one might be able to get around 150 Mh/s out of it? Also, the advantage of the $160 back plane is entirely cosmetic (i.e. to nicely hold several boards in a compact way)?   

[Transisto]

48W from SATA connector thats over 4A of current from 12V rail. Specs are 1.5A from this rail. You may SMELL trouble if you populate all slots...

I sometime have to use four pci-e to molex, ~300w,  48w is nothing. What rail ? psu rails are 18A or more

[sadpandatech]

48W from SATA connector thats over 4A of current from 12V rail. Specs are 1.5A from this rail. You may SMELL trouble if you populate all slots...

I believe you are mixing up your rails. What you are likely refering to is this, 'Another ATX addition was the +5sb rail for providing a small amount of standby power at 1.5a, even when the computer was nominally "off".'  Even on the cheapest little power supply I could reach and grab real quick with a sata power connector on it, I find that it is on the same 12v rail as the other 4pin molex are. On this el cheapo 250w PSU the 12v rail is rated at 13a...

[bcforum]

I currently mine with my own HDL code -- which is not performing very well yet (!).  I have deliberately not looked at or downloaded fpgaminer's code in order to avoid being the target of accusations.

The legal definition of 'clean room software' is much more flexible than most people assume.

You can look at fpgaminer's (or any other available) design.
You can write detailed specifications based on the design while looking at it. You have to be careful not to include any copyrighted material in the specification (IE code snippets.)
The same person can use the specifications to develop a new design.

The only limitation is: you cannot reference the original code while developing the new code.

For everyone else, the LX150 isn't supported by the free version of the Xilinx tools. You'll have to buy the full version ($5K?) to develop for this board.

[Dexter770221]

What I had in my mind is that pins on connector can be damaged. Of course modern computer PSU can deliver much much more current but pins on connectors are too thin and can burn. What I've missed is the info that one pin can deliver 1.5A of current, there are 3 pins for +12V so this connector will be close to its limits.

[deslok]

What I had in my mind is that pins on connector can be damaged. Of course modern computer PSU can deliver much much more current but pins on connectors are too thin and can burn. What I've missed is the info that one pin can deliver 1.5A of current, there are 3 pins for +12V so this connector will be close to its limits.

a sata connector will be fine for that kind of ampload, i've got a few sat->6pin pcie connectors i've been using for months with no issue

[fivebells]

For everyone else, the LX150 isn't supported by the free version of the Xilinx tools. You'll have to buy the full version ($5K?) to develop for this board.

Thanks.

[norulezapply]

Definitely interested in this!

Any prices for shipping to the UK if it's available?

[eldentyrell]

Also, the advantage of the $160 back plane is entirely cosmetic (i.e. to nicely hold several boards in a compact way)?  

The backplane has the 48W DC-DC power supply on it.  You won't be able to do much without a power supply!  That's why there's the option to get a smaller 12W version soldered directly on to the spartan card -- you need that option if you don't get the backplane.

The backplane also daisy-chains the six boards' JTAG connections, so you only need ONE usb-to-JTAG adapter instead of six.

[eldentyrell]

I sometime have to use four pci-e to molex, ~300w,  48w is nothing. What rail ? psu rails are 18A or more

The 1.2V supply is stepped down off of the 12V rail; that's where 99% of the power is drawn.

A tiny amount of power is used at 3.3V; this comes from the 5V rail on the SATA connector.  It's less than 50mA; basically negligible.  Only used for JTAG, the clock input pad, and VCCAUX.

I don't use the SATA 3.3V pin because it isn't always connected (e.g. molex-to-SATA adapters).

[eldentyrell]

I currently mine with my own HDL code -- which is not performing very well yet (!).  I have deliberately not looked at or downloaded fpgaminer's code in order to avoid being the target of accusations.

The legal definition of 'clean room software' is much more flexible than most people assume.

It's not the legal definition I'm worried about -- it's reputation.