Fancy a Bit of Full-On FPGA Fun? These Days, It's Far Cheaper Than You Might Have Feared!

FPGAs are freakishly good fun. Think of them as a miniature meccano set of microfabricated logic macro cells, able to be manipulated and morphed into most anything that one could imagine.

Commercially, they often step into play when there is a compute problem that is perhaps not quite able to be optimized enough, or even at all, in order overcome the limitations of conventional computing architecture.

Maybe there is a need to munch through mountains of massively parallel data, or often, the RF world will make use of digital tunable filters, implemented in the FPGA fabric itself.

While not quite as defined as alternatives like ASIC devices that sit at the other end of the scale — the circuitry of which will only ever see the same bits and bytes breezing through their bond wires — FPGAs feel a bit more freelance when it comes to figuring out their future career path.

The FPGA, or by its full name, a field programmable gate array, is a blank canvas of functional logical elements that can be routed between and betwixt one another, forming functional blocks that, eventually perform the logical functions that have been defined to them, at some higher level of device implementation.

Imagine them as a freshly plowed field, the crop that results will be down to whatever seed is planted, or in this case, the sequence of 1s and 0s that make up the bitstream that defines the device as it has been designed.

With these devices often sitting at the heart of the next next-gen technologies, it shouldn't be much of a surprise to lean that some of them are incredibly powerful devices, with peripherals to support the data transfer rates that these designs are destined to deal with.

Often found tasked with figuring out how to handle data rates and bandwidths of the highest order, even the devices that we see in the secondhand equipment market still have serial I/O capabilities that exceed tens of Gb/s — and the ability to flip that into any networking protocol you feel fitting.

And while you can find things like Kintex and Virtex chips on eBay for varying prices — fractions of the price you and I would pay, if we were ever quoted, well... There are very few of us sat here reading this article that need chips that are designed to handle 4 SFP optical fiber links at once, right? C'mon now, be honest.

What's more is that with the FPGA able to handle such a large percentage of the functional definition of the device it is designed into, the hardware that we see hosting and supporting these beasts is often a pretty application specific affair.

We'll often see them in NIC cards, or custom form factor compute modules, designed for drastically accelerating data intensive operations. This board below looks a bit funky — until you notice that despite it looking like two B-Edge M.2 PCI connectors... there's a pretty non-factory spec looking jagged edge, where this part of the card has been literally hack-saw-ed from whatever it was once part of.

Slashing hardware slashes the price it seems — these are cheap enough to impulse buy. Although it'd make a terrible coaster for $15 — the Virtex5 mounted on the module above still. stocks for $350, and along with it, you get everything needed to run it as intended — from external RAM and flash, and even the three-board mount PoL DC-DC converters would all be prohibitively expensive for any of us to design into our self-funded fabrications.

This Virtex6, shown below with four SFP fiber interfaces? That FPGA alone sells for a cool $1,157 USD — so long as you buy60 at once. Suddenly, $150 on eBay seems quite the steal. Especially as this is a complete card that hasn't had a hard time with a hacksaw...

But there's a big of a gotcha with these decimal place shifted dings'n'dents discounts... With no obvious signs of damage on the modules that haven't been macerated, we still are left with a bit of interpretation left when it comes to inferring the intended operation of all this IP..

What the hell do these things do?!

This high-tech hardware is going to be as far from the OSHW model as you can get, in regard to the specs, schematics, and design sources. We often see silk art on the back of these modules that bear familiar logos — Microsoft, Google, etc. You can bet they aren't going to connect your call through to the correct design team when you dial up the front desk at Cupertino.

Whereas the hardware itself is likely nothing too far from the FPGA vendor verified application circuit, any attempts to ask for, or tease out some technical tidbits from those tier 1 tyrants on this cards will probably be met with — at best silence, and at worse a cease and desist.

Though these devices — and the features they offer — make them favorable for applications involving high bandwidth, parallel data streams, which covers more than the latest in data communications and other such fun.

Recent trends in things like various approaches to cryptocurrency mining, or large scale LED video wall advertising are two applications that have found themselves well suited to FPGA devices, but ones with a slightly less unobtanium datasheet and price tag. You don't need a $7,500 Kintex UltraScale to shift signals to a HUB75E panel...

Shed some light on the matter

While driving large scale LED video display panels doesn't exactly demand digital I/O driven at such delicious speeds as an accelerator card destined to sit within a data center, even a reasonably sized panel of pixels can require a raft of signals routed to it at some rather reasonable speeds

If we take a look at one of the more recent line of commodity FPGA based controller cards — compact offerings from a company called Colorlight, we can start to get a high-level feel for what's on offer here in these bargain basement bitsmashers.

Colorlight 5A-75B

This is one of the cheapest of these boards that I'm babbling on about. Available for 10-15 dollars, it seems already suspiciously cheap - even as a scrap pull reclamation project — let alone a fully-functional FPGA board.

Front and center, we see a frequently featured member of the Lattice Semiconductor silicon — the LFE5U. Sure, it's no Spartan-7, but it's far from a simple silicon device. and a likely target for toying with when you've exceeded the more entry level iCE40.

Programmable parts from Lattice have been more than fairly well received within the hobbyist community due to favorable license terms that almost feel written with the OSHW world in mind, compared to some of the protection for the IP offered from other FPGA producers.

For the price of the FPGA itself, we find it sat on a board, complete with dual gigabit ethernet interfaces, external RAM, and more I/O than you can shake a significantly sized stick at.

Though the function of this board was figured out long before it was fabricated, remember, this is a FPGA — it's fully reconfigurable.

The stock bitstream sat on the configuration flash of the board will contain the logic to implement those insanely fast ethernet interfaces, interpret the incoming data, and in the space of a few clock cycles, appropriately convert it and chuck out out to the HUB75E panels connected to it.

Pushing pixels has become such a popular application that we can see there have been multiple manufacturers making sure that they have hardware solutions that can meet the needs of the massively expanding market.

With almost all of these cards looking like slight variations on a visually similar theme, a bit of casual digging down through the dozens of variants dominating the pages of DHGate, AliExpress et al, reveal that there are more than a few ways to get the job done.

Technical top trumps

While the Lattice based boards seem to be the most common cards in the collection, there are are a few lesser seen streaming receiver cards that make use of the FPGA offerings from other manufacturers

While they mostly all resemble a similar design — think how many of the boards we commonly see share a similar layout, due to the shared hardware they interface with. These cards similarly, have design specifications — dimensions dictated by the digital displays they are destined to drive.

Alternative ICs and clones?

While imitation is the most sincere form of flattery — so they say — the Altera Cyclone seen on this signal card shown below here is more alternative than a clone.

Looking somewhat like an SoM mounted on a support card, it's not unreasonable to assume that this could be where this design sources some of its layout suggestions from.

More likely however, the plated through-holes located along the exposed copper guard ring (square), which encompass the critical high-speed components suggest that, perhaps there might be a requirement to shield these parts against the fairly loud, 5V signals — which will be screaming out of the level shifters sitting between the serial I/O and the headers that serve to connect the screens to the system.

If the now Intel-owned IP offerings found on the flame-red FR4 stack up shown above aren't doing it for your digital design desires, if you aren't blown away by the Cyclone, maybe you might get a bit more excited by this Xilinx-based alternative...

This is SPARTA!

This fully-featured card seen below embraces the design ethos perhaps instilled by the namesake of the core controller sat at the center of the PCBA — the Spartan-6 series FPGA from Xilinx.

Variations on a theme

While we've seen color control cards containing custom configurable silicon from three of the major players in this market, these boards — designed to do one thing and one thing alone, very very well, are really some dastardly fast data converters.

They gulp in globs of data through those gigabit Ethernet interfaces, decoding it and reserializing it before sending it onwards to be slurped down by the slew of HUB75E panels strung to them.

Given LEDs aren't known for talking back — perhaps with the exception of when they have been exposed to a supply voltage far exceeding the specified Vcc... — these boards can usually be seen sporting a selection of level shifters, to make sure that the fairly feeble VCC_IO of the FPGA controller can be heard clearly by the LED panels.

As such, these level shifters are usually unidirectional units, which could be considered unfortunate if you wanted to do some bidirectional bit bashing with your bargain basement board. Thankfully, a few very clever hackers have figured out some pin-compatible, bidirectional level shifting suggestions for substitutions.

A little SMD level surgery, and all of those originally, output only off-board connectors are suddenly able to signal both ways, giving you a frankly rediculously priced FPGA development board that is not only robust enough to stand a first timer figuring out how to flash it, but also cheap enough to replace, if it ever falls foul of a wiring fault or such.

Compute modules — the latest craze!

What may be the most interesting of all of these freakishly cheap FPGA cards to have crossed my radar recently takes note of the modern trend of modularization.

That Colorlight 5A-75B we looked at first in this feature? How about that as a compute module? We see from Twitter user JohnnyWu — who seems to have some very desirable contacts at Colorlight — this design for what is effectively just that, the core function of the Colorlight controller board as a more mobile module level solution.

With a module in hand, JohnnyWu turned his attention to designing a breakout for this SO-DIMM format module, bereft of the level shifters that are needed to nudge the I/O voltage to that required for the usual application of driving HUB75 panels. But heck, I see an HDMI port — and that's a fair trade in my eyes! That's going to enable heaps of fun applications!

With all the attention that the recent Raspberry Pi CM4 is generating, and the portable projects that are potentially enabled by that pint sized puck of processing power... well, a feature-rich FPGA like the LFEU5 found on this SoM, in such a field portable form factor, for a price that of a few tens of dollars? That's freakin' fantastic.

As if this all wasn't already enough good news at once for your never ending list of projects that have yet to start phase one of prototyping... well, did I mention that thanks to the efforts of GitHub user wuxx that the there is an incredible amount of documentation for this SO-DIMM PCB set?