I recently acquired a Kobol Helios 64 (Introduction - Kobol Wiki). It has a AArch64 architecture and is powered by a Rockchip RK3399.
I wonder if it’s possible to install NixOS on it. The Rockchip RK3399 is supported by the community in different boards (such as NixOS on ARM/Firefly AIO-3399C - NixOS Wiki). Is it worth a try? Does anyone have some experience on the subject? 
It is probably worth a try, generally try to follow existing work on the subject.
Stick to the wiki and (if available) existing nixos-hardware configuration options to guide you.
Based on my limited experience with arm/x86 boards with quirks, you can get it done, but it might take a bit of time. If there is prior work on the SOC, then someone hopefully got most of that done though.
I finally got the time to dig into this a but more deeply.
Unfortunately, there is not much online about running NixOS on this hardware. All I could find was this pull-request (closed, seemingly due to frustration for random/non-reproducible issues): kobol/helios64: init by samueldr · Pull Request #318 · NixOS/nixos-hardware · GitHub
In the thread, one user (@Mic92) affirms to be running NixOS on the hardware with no issues: kobol/helios64: init by samueldr · Pull Request #318 · NixOS/nixos-hardware · GitHub
Relevant section of the user’s config: dotfiles/machines/blob64/configuration.nix at e9f775e68744db5e56c1c6f564e6fa166f625047 · Mic92/dotfiles · GitHub
None of the default NixOS sd-card images for aarch64 would boot on my Helios64. The LEDs would just turn on and nothing would happen, and I see nothing from tty. So I tried generating one following Mic92’s configuration (see above). Here is how I progressed so far: GitHub - sh4k095/nixos-helios64: NixOS sd-card image generator for Helios64 (I should add that the dedicated Armbian image boots without issues, and the device has been running it flawlessly for quite some time with ZFS, so I would exclude hardware issues).
I tried generating the image with nix build .#nixosConfigurations.helios64-installer.config.system.build.sdImage. The image builds successfully, but it won’t boot (same symptoms described above).
My experience in running NixOS on ARM is very limited, and with nothing to read from tty upon booting I am out of clues on how to get a bootable image. If you see something atrocious in my config, or have some other piece of advice, I’m all ears 
My helios64 is still up and works fine.
Hi there! I’m also interested in installing NixOS on my Kobol Helios64 NAS that I’ve been using with Armbian. Could you please help me and point me in the right direction to understand what is required to do it?
I’ve been using NixOS on my x64/AMD64 desktop/laptop machines for 3 years now so I’m already familiar with it. But not really on the ARM architecture. I believe that the Armbian build uses several kernel patches and dtb overlays to support the Helios64 hardware features. Can we get the same level of support with NixOS?
I think we had some profile in nixos-hardware for it with a Readme? I don’t need any patches to make it work dotfiles/machines/blob64/hardware-configuration.nix at db69f8b50c60678a6b34177d1d476973b2df151a · Mic92/dotfiles · GitHub
Thank you for your reply. I could only find the older Helios4 (not the newer Helios64) on nixos-hardware. By “making it work” you mean that it runs right? But does it fully supports the Helios64 hardware reliably? Meaning in example the eMMC flash full speed (HS400), the default fan speed control and cpu power/frequency profiles, the panel led bar and a reliable 2.5GbE NIC operation?
Never used the eMMC except for installing towboot, I had an NVME from the start, so can’t tell. I have my own simple fan control program. Both NICs work. I don’t have any 2.5GbE network to test if it works beyond 1Gbit/s.