The Fobu Is a Formidable Form Factor Bump for the Familiar Fomu FPGA Hardware Boards

When it comes to gaming, we love a bit of button bashing, and in my personal view, the more retro, the better the bashing.

That said, familiar readers will know that my view on the pinnacle of games console technology will always be the one, the only, N64 — I don't wander too far behind or in front of that behemoth from my youth...

So while we are no strangers to retro-tech gaming, such as this cute little 1" big, 1-bit Arduboy derivative, things have moved on a bit since the one-bit emulation days.

With the Arduboy made possible through an ATmega32U4, one wonders what magic could be made possible through the choice of a more modern-day MCU, perhaps something like the recent — and frankly, ridiculous — iMXRT1176 from NXP.

And it's not just us thinking that — thankfully, Twitter user Wenting (@zephray_wenting) had similar musings, having fortunately found themselves in possession of one of the NXP development boards for this powerful processor.

The i.MXRT family of MCU have seen a lot of love recently. If you haven't seen the solder party board brothers from @arturo182 yet — a pair of boards, one based on the RT1101, the other on the RT1062, you will no doubt have seen the phenomenally powerful Teensy 4 from Paul Stoffregen (aka PJRC), and the many many projects that showcase the sheer processing prowess that this family of parts can provide.

Leaning into the multimedia end of the MCU market, the RT family feature some comprehensive display capabilities, with DSI as a common interface on nearly all the family.

With this in mind, Wenting went ahead and chose to whip up a quick proof-of-concept for his envisioned emulator display, with a whopping 162Mbps MIPI DSI interface, implemented over the fabric of a few bodge wires.

That's some serious soldering skill, and patience that would have sent many of us off to the PCB fab for a breakout board: respect where it's due!

While that panel is lit up, let's take a look at it in a little more detail.

Reflecting on transflective displays...

I love the days when I learn something new. Today, Duolingo got ducked for the knowledge that there are FINALLY backlit, transflective LCD screens that are available to us mere mortals!

A transflective display is a technology we have touched on before, and is not dissimilar to how an ePaper display functions, in principle.

An electrostatic force is developed between a set of electrodes, the potential of which is related to the physical displacement of an internal, physical marker, with colors deposited upon it.

As the field potential is adjusted, as is the rotation of the physical pixel, and as such, the color that is shown to the viewer.

Normally, as is often the case with ePaper displays, for example, we don't see backlighting in these panels, simply because the use case is often outdoor, sunlit applications, where a backlight is unnecessary, and reflected light serves just fine.

However, like the screen seen in the OLPC XO laptop (shown above), the 320 x 320 pixel display hacked on to the host board seen above features two modes of operation — backlit (transmissive), and passive (transflective)!

Looking above, we can see how the display is arranged, with the transflective pixel array spaced such that light is able to pass through the matrix, allowing for a backlit, transmissive RGB operation, and a far more subtle, monochrome transflective display mode, shown below.

That's enough dishing on the display...

So, with a powerful processor, and a lovely looking LCD, what is it that Wenting is up to here? Let's drop a render and dig in.

In Wenting's own words:

"Here is a block diagram of the Fobu r0.3. I am mainly focusing on 2 use cases: 1. high quality chiptune (FPGA assisted or emulated) & music (flac, wav, etc.) playback 2. docked (via USB Type-C) FPGA or emulator retro gaming"

Woah.

The Fobu — with naming somewhat certainly inspired by the Fomu boards, does away with the USB-port sized PCB, and bumps it up to a keyfob-sized PCBA, and good gosh does that moderate size increase leave a hell of a lot of room for processing power.

There's the i.MX RT 1176 sat at the centre, capably interfaced to a whopping Xilinx Spartan-7 XC7S25 FPGA, and a whole suite of peripheral parts that look set to make the Fobu a formidable, pocket-sized retro gaming platform.

Note how audio and video are routed through the MCU: The FPGA could simply output video and audio at platform native resolution and sample rate. The ARM will do the scaling and sample rate conversion, and handle the LCD/3.5mm/Type C switch over transparently.

We note the a Cirrus Logic CS43131, one of the same family of high-quality stereo DACs that we recently saw implemented on Sam Littlewood's sd2snes_ecp5 project we featured just the other day.

The very interesting part in my eyes is the inclusion of the Toshiba TC358777 DSI to DP bridge, allowing the i.MX to choose to output to the devices transflective display, or scale up the pixel resolution, and pass the DSI signals through to the DSI/DP bridge, to be sent out over USB-C port, over alt-mode USB-DP. That's very cool, and I can't wait to see that working!

Speaking of seeing it working...

Wenting is way past the render phase, with some strikingly beautiful boards in hand, it's likely only a matter of time before we see this formidable Fobu board booting up some retro emulation button bashing!

With this strong a starting ground — as we go to print — we almost feel that by the time you're reading this, Wenting will have wrangled the Fobu up past the fun of bringing up such a complex board — but we shall wait and see, updating accordingly of course as soon as we see a boot screen from him over on Twitter (@zephray_wenting)!