For armv6 and armv7, there is no build infrastructure setup by NixOS, and they are not supported platforms. AFAIUI, there would be a need for both support and build infrastructure. For the time being, it is assumed armv6 and armv7 will be community-supported.
As for AArch64 (64 bits ARM), the binaries are (now) built by hydra, and is an in-progress supported platform. Issue #33745 tracks the AArch64 support progress.
It looks like Hydra is now building the SD image for AArch64.
Though, looks like “ZHF” (zero-hydra-failures) is a big part of why it’s not out yet.
- 18.03 Zero Hydra Failures - aarch64 edition · Issue #32326 · NixOS/nixpkgs · GitHub
- Hydra - nixos:release-18.03-aarch64 → https://hydra.nixos.org/eval/1453087
I’ll be asking around for details and/or updates to the tracking issue, mainly to see what’s missing.