litepcie VS SpinalHDL

Hi folks. :)

I'm so glad that my hit-and-run post has been so useful. After seeing Fabien's blog post I did a quick search and it turns out that the solution has spread fairly broadly to other forums. My choice of 0x33 was arbitrary so makes a nice canary for seeing it spread out.

My use case was (and remains) having a Xilinx Artix 7 FPGA in an external Thunderbolt 3 enclosure for testing the development of DSP accelerators using open source tooling. I didn't want to have the FPGA board inside the PC to be able to swap it to my laptop easily, because it produces a lot of heat, and so when I misused the PCIe soft core (litePCIe: https://github.com/enjoy-digital/litepcie/) it doesn't take down the OS. Being able to reload the FPGA and effectively hotplug the device has been very helpful.

Since I knew my issue was around hotplugging I searched for information around PCIe hotplugging and I think (it was two years ago...) that I found the answer from one of these two threads. Both mention the option of reserving PCIe addresses for hotplug busses as a workaround, and a workaround was all I needed.

https://www.spinics.net/lists/linux-pci/msg64841.html

https://review.coreboot.org/c/coreboot/+/35946

dmesg and the various kernel logs are my first stop for any odd behavior on Linux. Especially with any state change to a device (plugging in, turning on, removing, reconfiguring etc) the kernel logs tend to give invaluable info.

I had already been looking at eGPU forums to choose the Thunderbolt 3 enclosure (ended up with the ORI-SCM2T3-G40-GY) and there were various discussions of hotplugging issues there, but I don't think I found the specific kernel options to fix it there.

Check out this docs page for the kernel parameters:

You could try to implement a PCIe root complex for FOSS SoCs, connecting to e.g. Wishbone as the main bus. There's already some DDR3 controller (or this one) and USB Host controller out there, and even device-side PCIe, but no FOSS host-side PCIe that I know of. Probably quite a difficult job though, even sticking to the lower-speed PCIe 1.

I'd love to see textual preprocessors kinda banned. Or at least done upstream and outside of the language. You can't both be and also have a textual preprocessor defined internally. It doesn't work.

I really like what Zig and C++ are doing with `const`.

https://ikrima.dev/dev-notes/zig/zig-metaprogramming/

Have you looked at Spinal?

https://github.com/SpinalHDL/SpinalHDL

https://spinalhdl.github.io/SpinalDoc-RTD/master/index.html

Many companies do just write entire modern SoCs in straight Verilog (maybe with some autogenerated Verilog hacked in there) with no other major organization tools aside from the typical project management stuff. The load-store unit of a modern CPU alone easily exceeds 10k lines of Verilog. It's a similar thing as people who work with kernels—after all, the page table management code in a modern operating system like Linux is absolutely monstrous but still people are able to understand it well enough to be able to make the changes they need and get out.

If you are interested in other languages which hope to make this sort of stuff easier, I'd recommend taking a look at design productivity languages like Chisel and it's associated Chipyard [1], SpinalHDL [2], and Bluespec [3]. Each of these are meant to make defining extremely complex hardware more manageable for humans and there's a lot of interesting work going on right now with each of them.

[1] https://github.com/ucb-bar/chipyard

[2] https://github.com/SpinalHDL/SpinalHDL

[3] https://github.com/B-Lang-org/bsc

I have just found that SpinalHDL also implemented two halves of the fully registered buffer in Stream.scala.

Don’t forget SpinalHDL that was forked off of Chisel 2 I believe. These DSLs really leveraged the software features of Scala to help build generalised/modular systems. And are generally a quality of life improvement in the language features available.

A lot of reuse from other FOSH projects, including Litex, SpinalHDL, betrusted & u/alexforencich verilog-wishbone. Thanks to all of them :-)

You could try to implement a PCIe root complex for FOSS SoCs, connecting to e.g. Wishbone as the main bus. There's already some DDR3 controller (or this one) and USB Host controller out there, and even device-side PCIe, but no FOSS host-side PCIe that I know of. Probably quite a difficult job though, even sticking to the lower-speed PCIe 1.