PfhorSlayer

The problem with doing that is it would require significantly more space in that spec. At a minimum, one offset for each possible mip level. That data needs to be moved around the GPU internally quite a bit, crossing clock domains and everything else, and would require a ton of extra registers to keep track of. Putting it in a ROM is basically free - a pair of BRAM versus a ton of registers (and the associated timing considerations), the BRAM wins almost every time.

Implementing PCIe in the fabric without using the hard IP would be foolish, and definitely not the kind of thing I'd enjoy spending my time on! The design makes extensive use of the DSP48E2 and various BRAM/URAM blocks available in the fabric. I don't have exact numbers off the top of my head, but roughly it's ~500 DSP units (primarily for multiplication), ~70k LUTs, ~135k FFs, and ~90 BRAMs. Porting it to a different device would be a pretty significant undertaking, but would not be impossible. Many of the DSP resources are inferred, but there is a lot of timing stuff that depends on the DSP48E2's behavior - multiple register stages following the multiplies, the inputs are sized appropriately for those specific DSP capabilities, etc.

The hardened DisplayPort IP is connected to the ARM cores, and requires a significant amount of configuration and setup. FuryGpu's firmware primarily handles interfacing with that block: setting up descriptor sets to DMA video frame and audio data from memory (where the GPU has written it for video, or where the host has DMA'd it for audio), responding to requests to reconfigure things for different resolutions, etc. There's also a small command processor there that lets me do various things that building out hardware for doesn't make sense - moving memory around with the hardened DMA peripheral, setting up memory buffers used internally by the GPU, etc. If I ever need to expose a VGA interface in order to have motherboards treat this as a primary graphics output device during boot, I'd also be handling all of that in the firmware.

Let's be clear here, this is a toy. Beyond being a fun project to work on that could maybe get my foot in the door were I ever to decide to change careers and move into hardware design, this is not going to change the GPU landscape or compete with any of the commercial players. What it might do is pave the way for others to do interesting things in this space. A board with all of the video hardware that you can plug into a computer with all the infrastructure available to play around with accelerating graphics could be a fun, if extremely niche, product. That would also require a *significant* time and money investment from me, and that's not something I necessarily want to deal with. When this is eventually open-sourced, those who really are interested could make their own boards.

One thing to note that is that while the US+ line is generally quite expensive (the higher end parts sit in the five-figures range for a one-off purchase! No one actually buying these is paying that price, but still!), the Kria SOMs are quite cheap in comparison. They've got a reasonably-powerful Zynq US+ for about $400, or just $350ish the dev boards (which do not expose some of the high-speed interfaces like PCIe). I'm starting to sound like a Xilinx shill given how many times I've re-stated this, but for anyone serious about getting into this kind of thing, those devboards are an amazing deal.

In general, yes. However, the Kria series are amazingly good deals for what you get - a quite powerful Zynq US+ part and a dev board for like $350.

You've nailed the problem directly on the head. For hitting 60Hz in FuryGpu, I actually render at 640x360 and then pixel-double (well, pixel->quad) the output to the full 720p. Even with my GPU cores running at 400MHz and the texture units at 480MHz with fully fixed-function pipelines, it can still struggle to keep up at times.

I do not doubt that a shader core could be built, but I have reservations about the ability to run it fast enough or have as many of them as would be needed to get similar performance out of them. FuryGpu does its front-end (everything up through primitive assembly) in full fp32. Because that's just a simple fixed modelview-projection matrix transform it can be done relatively quickly, but having every single vertex/pixel able to run full fp32 shader instructions requires the ability to cover instruction latency with additional data sets - it gets complicated, fast!

Next blog post will be covering exactly that! Probably going to do a multi-part series - first one will be the PCB schematic/layout, then the FPGA interfaces and testing, followed by Windows drivers.

I'm in the process of actually trying to work out what would be feasible performance-wise if I were to spent the considerable effort to add the features required for base D3D support. It's not looking good, unfortunately. Beyond just "shaders", there are a significant amount of other requirements that even just the OS's window manager needs to function at all. It's all built up on 20+ years of evolving tech and for the normal players in this space (AMD, Nvidia, Intel, Imagination, etc.) it's always been an iterative process.

Funny enough, that's exactly where this project started. After I built his 8 bit breadboard computer, I started looking into what might be involved in making something a bit more interesting. Can't do a whole lot of high-speed anything with discrete logic gates, so I figured learning what I could do with an FPGA would be far more interesting.

If the FPGA contains a hard PCIe IP that can act as a host and the proper transceivers and the CPU implemented all of the necessary things to interface with it, it'd be about as difficult as writing a driver for any other machine. Actually building a board for the FPGA with all of the required power supplies, peripherals, and a PCIe host is not a trivial undertaking however, and an FPGA with a hard PCIe controller generally isn't cheap!

It's actually modeled very closely after Vulkan, but I couldn't think of a clever re-wording that would fit that and "Fury" together. I would have taken Vulkan's API as-is, but the hardware itself is fixed-function and does not support shaders, which Vulkan's API takes for granted; if you've seen Vulkan applications, it's nearly identical except that the pipelines do not include shaders. The way Vulkan (and D3D12) build and submit command buffers very closely matches how the hardware actually works, so it felt like a good fit.

If the hardware were ever to support actual shaders, I would be writing a full D3D-driver stack for it as Windows would then be able to utilize the GPU as a "real" GPU, rather than as just a display controller. As things are now, Windows has no idea that the device can do anything other than display a pre-composited desktop. When an application wants to utilize its 3D rendering capabilities, the driver actually does a mode swap similar to how the old Voodoo cards used to work - the OS still thinks it's rendering the desktop, but the hardware is actually displaying the application's content.

Hey! I'm the developer of the FuryGPU, and it's very cool to see others working in a similar space - Doom is neat but Quake is where 3D graphics really came into their own.

For anyone curious, FuryGPU is a full mid-90s-era GPU built from the ground up which covers the entire stack of both hardware and software development. I designed a custom PCB to expose the PCIe lanes on the Kria K26 (Zynq UltraScale+) FPGA and allow for fast host-GPU communication, built and optimized the actual GPU hardware, wrote both an entirely custom graphics API to drive it as well as Windows drivers to have the OS interact with the hardware correctly, and finally ported Quake to that new API. It's been about three years of work and is still my first and only FPGA project.

Once everything is "finished," I do plan on open-sourcing the project. When and what that will look like depends on a lot of factors, but I've nearly ticked all the boxes I set for myself originally so it probably won't be too far in the future.

Thanks for the plug!