feat(sakuya): system.build.sdImage

systems/sakuya/nixos.nix

@@ -1,11 +1,15 @@
 {
+  pkgs,
   config,
+  modulesPath,
   meta,
   ...
 }: {
   imports = let
     inherit (meta) nixos;
   in [
+    (modulesPath + "/installer/sd-card/sd-image.nix")
+    nixos.base
     nixos.sops
     nixos.tailscale
   ];
@@ -13,9 +17,47 @@
     grub.enable = false;
     generic-extlinux-compatible.enable = true;
   };
+  sdImage = let
+    # TODO: boot0 requires additional BSL processing applied to the uboot bin:
+    # https://github.com/longsleep/build-pine64-image/tree/master/u-boot-postprocess
+    uboot = pkgs.ubootPine64;
+    # Arch Linux ARM has already done this for us...
+    ubootPrepackagedARM = pkgs.fetchurl {
+      url = "http://os.archlinuxarm.org/os/allwinner/boot/pine64/u-boot-sunxi-with-spl.bin";
+      sha256 = "sha256-qT5M93p/t7eW6lqZq4dC8z8BkYcQOkTgiN+jZatObuo=";
+    };
+    ubootProcessed = ubootPrepackagedARM;
+  in {
+    postBuildCommands = ''
+      dd if=${ubootProcessed} of=$img bs=8k seek=1
+    '';
+    # taken from sd-image-aarch64.nix
+    populateFirmwareCommands = let
+      configTxt = pkgs.writeText "config.txt" ''
+        [all]
+        # Boot in 64-bit mode.
+        arm_64bit=1
+
+        # U-Boot needs this to work, regardless of whether UART is actually used or not.
+        # Look in arch/arm/mach-bcm283x/Kconfig in the U-Boot tree to see if this is still
+        # a requirement in the future.
+        enable_uart=1
+
+        # Prevent the firmware from smashing the framebuffer setup done by the mainline kernel
+        # when attempting to show low-voltage or overtemperature warnings.
+        avoid_warnings=1
+      '';
+    in ''
+      cp ${configTxt} firmware/config.txt
+    '';
+    populateRootCommands = ''
+      mkdir -p ./files/boot
+      ${config.boot.loader.generic-extlinux-compatible.populateCmd} -c ${config.system.build.toplevel} -d ./files/boot
+    '';
+  };
 
   fileSystems."/" = {
-    device = "/dev/disk/by-uuid/44444444-4444-4444-8888-888888888888";
+    device = "/dev/disk/by-label/NIXOS_SD";
     fsType = "ext4";
   };