how to use cachix? typical build commands?

[dckc]

This looks really cool (I found it via the Summit abstracts), but I'm struggling a bit trying to figure out which end is up. Here's hoping you have some free time to answer some remedial nix questions. I completely understand if not...

Based on ci logs, I tried cloning at e6c03d0 and then:

$ cachix use dlr-ft
Configured https://dlr-ft.cachix.org binary cache in /home/connolly/.config/nix/nix.conf

$ nix build .#packages.x86_64-linux.atf-aarch64-zcu102
[1/1/3 built, 25 copied (497.4/497.5 MiB), 104.8 MiB DL] building openssl-aarch64-unknown-linux-gnu-3.0.13 (buildPhase): aarch64-unknown-linux-gnu-error: interrupted by the user

I interrupted it because I expected to get cache hits for everything. I don't understand why any local builds are happening.

Likewise, nix build .#seL4-kernel-x64 starts building binutils.

nix build .#seL4-deps seems to be a noop... I guess that's because I did direnv enable and the deps were grabbed at that point.

What are the target packages that you typically use? Each ci build seems to do about 20 of them. It would be nice if the README told a little about what a few of those do.

nix flake show lists a whole bunch of stuff, but I'm not even sure which parts of it to pick out to feed to nix build. I guess it's starting to make sense...