fpga

526 Articles

“Brain In A Vat” 6502

November 3, 2020 by 39 Comments

The 6502 was a revolutionary processor for its time. Offered at a small fraction of the cost of other processors available when it was released, it became adopted in such iconic computers at the Atari 2600, the Apple II, the NES, and the Commodore 64. For that reason it’s still extremely popular among retrocomputing enthusiasts who will often go to great lengths to restore these computers or build them from scratch. [jamesbowman] had an idea to build a 6502-based computer with the processor only, leaving the rest of the computer up to an FPGA.

He describes the system as a “brain in a vat” since a real 6502 is used as the “brain” and all other functions are passed off to the FPGA. In his build he uses an FPGA board with built-in graphics abilities, but the truly interesting part of this build is how the FPGA handles memory. If a particular value is placed on the data bus of the 6502, it loops forever through the entire memory and executes all of the instructions it finds. This saved a lot of time getting this system up and running, and he is able to demonstrate it by showing a waveform on the video output of the device.

Of course you can take an FPGA and emulate an entire computer based on a 6502, but using the actual silicon in a build like this really ensures that the user can learn and understand the hardware involved without some of the other tedium of doing things such as converting old video signals to HDMI for example. It’s a great take on retrocomputing that we expect to see more of in the future.

AMD Acquires Xilinx For $35 Billion

October 27, 2020 by 45 Comments

News this morning that AMD has reached an agreement to acquire Xilinx for $35 Billion in stock. The move to gobble up the leading company in the FPGA industry should come as no surprise for many reasons. First, the silicon business is thick in the age of mergers and acquisitions, but more importantly because AMD’s main competitor, Intel, purchased the other FPGA giant Altera back in 2015.

Primarily a maker of computer processors, AMD expands into the reconfigurable computing market as Field-Programmable Gate Arrays (FPGA) can be adapted to different tasks based on what bitstream (programming information written to the chips) has been sent to them. This allows the gates inside the chip to be reorganized to perform different functions at the hardware level even after being put into products already in the hands of customers.

Xilinx invented the FPGA back in the mid-1980s, and since then the falling costs of silicon fabrication and the acceleration of technological advancement have made them evermore highly desirable solutions. Depending on volume, they can be a more economical alternative to ASICs. They also help with future-proofing as technology not in existence at time of manufacture — such as compression algorithms and communications protocols — may be added to hardware in the field by reflashing the bitstream. Xilinx also makes the Zynq line of hybrid chips that contain both ARM and FPGA cores in the same device.

The deal awaits approval from both shareholders and regulators but is expected to be complete by the end of 2021.

Throwing Down The FPGA Gauntlet

October 11, 2020 by 29 Comments

Gauntlet is a well-known arcade game from 1985 with many sequels and ports to more modern architectures such as Xbox and GameCube. Thanks to its popularity and relative age, the original arcade cabinet is well documented with the schematics available online. It was regarded as the most complex and ambitious hardware Atari had ever developed at the time it was released. In what can only be described as an absolute labor of love, [Alex] has recreated the arcade hardware on the Pipistrello FPGA board.

The project can actually play Gauntlet, Gauntlet II, and Vindicators II as they all ran on the same hardware. Four joysticks are supported so up to four players can play, though the EEPROM is emulated in RAM so high scores are reset when the device is powered down. The FPGA is almost out of space and can’t quite squeeze in the SRAM needed. So an SRAM expansion daughterboard is required; nothing a quick board run from our favorite purple PCB manufacturer can’t solve.

In the repo is an incredible write-up detailing the system, how it works, and the process of debugging it. This project also includes a complete simulation of the TMS5220 Voice Synthesis Processor, as Gauntlet was the first coin-operated arcade machine with a voice synthesizer. Getting the video correct was particularly tricky and it took several tries to get the color palette and motion looking right. Since [Alex] didn’t have access to an original Gauntlet arcade cabinet, they had to make do with MAME. After writing a test to make sure the FPGA was working correctly, there were differences between the MAME emulation and the FPGA output. To help out, [Colin Davies] came to the rescue. After [Colin] hooked up an original Gauntlet Arcade PCB with the motion test loaded up, the test showed that the FPGA had the correct behavior.

During development [Alex] actually simulated several frames of the game in ISIM (at a whopping 90 seconds per frame or 90 minutes per in-game second). Using ISIM allowed them to compare system state to MAME and validate the design much faster as they could better inspect the interworkings of the different modules. Using a clever trick of grabbing state from MAME after a few seconds, they primed the FPGA state and saved themselves a few hours of simulation.

If you’re looking to get into old hardware style arcade game development, give the browser-based 8bitworkshop IDE a spin. Or start with something a little smaller in scope and size with this adorable mini CRT arcade cabinet.

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An FPGA Video Player Built Just For Fun

September 26, 2020 by 8 Comments

Sometimes, projects are borne out of neccessity; a fix for a problem that needs to be solved. Other times, they’re done just for the love of creation and experimentation. [ultraembedded]’s FPGAmp media player falls under the latter, and served as a great learning experience along the way.

The aim of FPGAmp is to play back a variety of media files on the Arty A7 development board, based around the Xilinx Artix-7 FPGA. Capable of playing back MJPEG video at 800 x 600 resolution and 25 fps, it’s also able to play back MP3s as well for stereo audio. Demonstrating the device on Twitter, [ultraembedded] notes that the method of using an LED to do SPDIF optical audio output isn’t legit, but does work. A later update switches to using a dedicated audio output board with the Arty A7 platform, featuring an excellent song from The Cardigans.

Using a RISC V processor core and a hardware JPEG decoder, we imagine [ultraembedded] really sharpened their FPGA skills with this project. Particularly in the wake of the sale of ARM to NVIDIA, RISC V continues to gain relevance in the hardware community. We were lucky enough to feature a keynote at last year’s Supercon, with Megan Wachs speaking on the technology. Video after the break.

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What’s Inside An FPGA? Ken Shirriff Has (Again) The Answer

September 21, 2020 by 13 Comments

FPGAs are somewhat the IPv6 of integrated circuits — they’ve been around longer than you might think, they let you do awesome things that people are intrigued by initially, but they’ve never really broke out of their niches until rather recently. There’s still a bit of a myth and mystery surrounding them, and as with any technology that has grown vastly in complexity over the years, it’s sometimes best to go back to its very beginning in order to understand it. Well, who’d be better at taking an extra close look at a chip than [Ken Shirriff], so in his latest endeavor, he reverse engineered the very first FPGA known to the world: the Xilinx XC2064.

If you ever wished for a breadboard-friendly FPGA, the XC2064 can scratch that itch, although with its modest 64 configurable logic blocks, there isn’t all that much else it can do — certainly not compared to even the smallest and cheapest of its modern successors. And that’s the beauty of this chip as a reverse engineering target, there’s nothing else than the core essence of an FPGA. After introducing the general concepts of FPGAs, [Ken] (who isn’t known to be too shy to decap a chip in order to look inside) continued in known manner with die pictures in order to map the internal components’ schematics to the actual silicon and to make sense of it all. His ultimate goal: to fully understand and dissect the XC2064’s bitstream.

Of course, reverse engineering FPGA bitstreams isn’t new, and with little doubt, building a toolchain based on its results helped to put Lattice on the map in the maker community (which they didn’t seem to value at first, but still soon enough). We probably won’t see the same happening for Xilinx, but who knows what [Ken]’s up to next, and what others will make of this.

I’m Sorry Dave, You Shouldn’t Write Verilog

September 4, 2020 by 54 Comments

We were always envious of Star Trek, for its computers. No programming needed. Just tell the computer what you want and it does it. Of course, HAL-9000 had the same interface and that didn’t work out so well. Some researchers at NYU have taken a natural language machine learning system — GPT-2 — and taught it to generate Verilog code for use in FPGA systems. Ironically, they called it DAVE (Deriving Automatically Verilog from English). Sounds great, but we have to wonder if it is more than a parlor trick. You can try it yourself if you like.

For example, DAVE can take input like “Given inputs a and b, take the nor of these and return the result in c.” Fine. A more complex example from the paper isn’t quite so easy to puzzle out:

Write a 6-bit register ‘ar’ with input
defined as ‘gv’ modulo ‘lj’, enable ‘q’, synchronous
reset ‘r’ defined as ‘yxo’ greater than or equal to ‘m’,
and clock ‘p’. A vault door has three active-low secret
switch pressed sensors ‘et’, ‘lz’, ‘l’. Write combinatorial
logic for a active-high lock ‘s’ which opens when all of
the switches are pressed. Write a 6-bit register ‘w’ with
input ‘se’ and ‘md’, enable ‘mmx’, synchronous reset
‘nc’ defined as ‘tfs’ greater than ‘w’, and clock ‘xx’.

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Write In PipelineC For FPGAs

August 16, 2020 by 15 Comments

The best thing about field-programmable gate arrays (FPGAs), when you have a massively parallel application, is that everything runs in parallel. The worst thing about FPGAs, when you need a lot of stuff to happen in sequence, is that everything runs in parallel. If you have a multi-step computation, for example, you need to break it up into chunks, figure out the timing between them, and make sure that each chunk clears before it is fed new data. This is pipelining, and taking care of all the low-level details yourself is one of the things that can sometimes make FPGA a four-letter word beginning with “F”.

[Julian Kemmerer]’s PipelineC is a C-like language that compiles down into VHDL so that you can use it in an FPGA, and it does the pipelining for you. He has examples of how you’d use it to construct a simple state machine, and after you’ve written a few hundred state machines the long way, you’ll know why this is a good idea.

PipelineC isn’t the only high level synthesis language out there, but it sits in an interesting place. It doesn’t take care of memory or define interfaces. It just takes care of pipelining. We haven’t tried it out yet, but it looks like it would be interesting for moderately complex projects, where the mechanics of pipeline signalling is a hassle, but you don’t require the deluxe treatment. Check it out, and if you like it, let us (and [Julian], natch) know.

If you want to dive head-first into pipelining, give [Al Williams]’ two-part mini-series a look.

Pipeline graphic CC BY-SA 3.0 by CBurnett