generate probably-non-functional firmware image for gl-ar750

default.nix

@@ -16,10 +16,21 @@ let
   kernel = callPackage ./kernel {
     inherit (config.kernel) config checkedConfig;
   };
-in {
+  outputs = rec {
-  outputs = {
     inherit squashfs kernel;
-    default = nixpkgs.pkgs.runCommand "both-kinds" {} ''
+    uimage = kernel.uimage {
+      inherit (device.boot) loadAddress entryPoint;
+      inherit (kernel) vmlinux;
+    };
+
+    combined-image = nixpkgs.pkgs.runCommand "firmware.bin" {
+      nativeBuildInputs = [ nixpkgs.buildPackages.ubootTools ];
+    } ''
+      dd if=${uimage} of=$out bs=128k conv=sync
+      dd if=${squashfs} of=$out bs=128k conv=sync,nocreat,notrunc oflag=append
+    '';
+
+    directory = nixpkgs.pkgs.runCommand "both-kinds" {} ''
        mkdir $out
        cd $out
        ln -s ${squashfs} squashfs
@@ -29,6 +40,9 @@ in {
     # out what's in the image, which is nice if it's unexpectedly huge
     manifest = writeText "manifest.json" (builtins.toJSON config.filesystem.contents);
   };
+in {
+  outputs = outputs // { default = outputs.${device.outputs.default}; };
+
   # this is just here as a convenience, so that we can get a
   # cross-compiling nix-shell for any package we're customizing
   inherit (nixpkgs) pkgs;

devices/gl-ar750.nix

@@ -1,3 +1,21 @@
+# GL.INet GL-AR750 "Creta" travel router
+#  - QCA9531 @650Mhz SoC
+#  - dual band wireless: IEEE 802.11a/b/g/n/ac
+#  - two 10/100Mbps LAN ports and one WAN
+#  - 128MB DDR2 RAM / 16MB  NOR Flash
+#  - "ath79" soc family
+# https://www.gl-inet.com/products/gl-ar750/
+
+# I like GL.iNet devices because they're relatively accessible to
+# DIY users: the serial port connections have headers preinstalled
+# and don't need soldering
+
+# The default output is a combined image containing a kernel
+# packaged as a "uimage" and initrd filesystem. This can be
+# downloaded to the device using TFTP and then written into
+# flash, or if PHRAM suport is enabled (handy for development)
+# unpacked and run directly into RAM
+
 {
   system = {
     crossSystem = {
@@ -8,4 +26,55 @@
       };
     };
   };
+  kernel = {
+    checkedConfig = {
+      "MIPS_RAW_APPENDED_DTB" = "y";
+    };
+    config = {
+      # this is all copied from nixwrt ath79 config. Clearly not all
+      # of it is device config, some of it is wifi config or
+      # installation method config or ...
+      "BLK_DEV_INITRD" = "n";
+      "CMDLINE_PARTITION" = "y";
+      "DEBUG_INFO" = "y";
+      "DEVTMPFS" = "y";
+      "EARLY_PRINTK" = "y";
+      "FW_LOADER" = "y";
+      # we don't have a user helper, so we get multiple 60s pauses
+      # at boot time unless we disable trying to call it
+      "FW_LOADER_USER_HELPER" = "n";
+      "IMAGE_CMDLINE_HACK" = "n";
+      "IP_PNP" = "y";
+      "JFFS2_FS" = "n";
+      "MIPS_RAW_APPENDED_DTB" = "y";
+      "MODULE_SIG" = "y";
+      "MTD_CMDLINE_PARTS" = "y";
+      "MTD_SPLIT_FIRMWARE" = "y";
+      "PARTITION_ADVANCED" = "y";
+      "PRINTK_TIME" = "y";
+      "SQUASHFS" = "y";
+      "SQUASHFS_XZ" = "y";
+      "ASN1" = "y";
+      "ASYMMETRIC_KEY_TYPE" = "y";
+      "ASYMMETRIC_PUBLIC_KEY_SUBTYPE" = "y";
+      "CRC_CCITT" = "y";
+      "CRYPTO" = "y";
+      "CRYPTO_ARC4" = "y";
+      "CRYPTO_CBC" = "y";
+      "CRYPTO_CCM" = "y";
+      "CRYPTO_CMAC" = "y";
+      "CRYPTO_GCM" = "y";
+      "CRYPTO_HASH_INFO" = "y";
+      "CRYPTO_LIB_ARC4" = "y";
+      "CRYPTO_RSA" = "y";
+      "CRYPTO_SHA1" = "y";
+      "ENCRYPTED_KEYS" = "y";
+      "KEYS" = "y";
+    };
+  };
+  outputs.default = "combined-image";
+  boot = {
+    loadAddress = "0x80060000";
+    entryPoint  = "0x80060000";
+  };
 }

devices/qemu.nix

@@ -1,3 +1,7 @@
+# This "device" generates images that can be used with the QEMU
+# emulator. The default output is a directory containing separate
+# kernel (uncompressed vmlinux) and initrd (squashfs) images
+
 {
   system = {
     crossSystem = {
@@ -446,4 +450,5 @@
       VIRTIO_NET = "y";
     };
   };
+  outputs.default = "directory";
 }

kernel/default.nix

@@ -34,9 +34,9 @@ let
       cp -a . $out
     '';
   };
-in
+in rec {
-{
   vmlinux = callPackage ./vmlinux.nix {
     inherit tree config checkedConfig;
   };
+  uimage = callPackage ./uimage.nix { };
 }

kernel/uimage.nix

@@ -0,0 +1,42 @@
+{
+  lzma
+, stdenv
+, ubootTools
+} :
+let
+  objcopy = "${stdenv.cc.bintools.targetPrefix}objcopy";
+in {
+  vmlinux
+# , commandLine
+# , fdt ? null
+, entryPoint
+# , extraName ? ""                # e.g. socFamily
+, loadAddress
+} :
+  # patchDtbCommand = if (fdt != null) then ''
+  #   ( cat vmlinux.stripped ${fdt} > vmlinux.tmp ) && mv vmlinux.tmp vmlinux.stripped
+  # '' else ''
+  #   echo patch-cmdline vmlinux.stripped '${commandLine}'
+  #   patch-cmdline vmlinux.stripped '${commandLine}'
+  #   echo
+  # '';
+stdenv.mkDerivation {
+  name = "kernel.image";
+  phases = [ "buildPhase" "installPhase" ];
+  nativeBuildInputs = [
+    # patchImage
+    lzma
+    stdenv.cc
+    ubootTools
+  ];
+  buildPhase = ''
+    ${objcopy} -O binary -R .reginfo -R .notes -R .note -R .comment -R .mdebug -R .note.gnu.build-id -S ${vmlinux} vmlinux.stripped
+    # {patchDtbCommand}
+    rm -f vmlinux.stripped.lzma
+    lzma -k -z  vmlinux.stripped
+    mkimage -A mips -O linux -T kernel -C lzma -a ${loadAddress} -e ${entryPoint} -n 'MIPS Liminix Linux ' -d vmlinux.stripped.lzma kernel.image
+  '';
+  installPhase = ''
+    cp kernel.image $out
+  '';
+}

modules/base.nix

@@ -31,6 +31,7 @@ in {
       };
       checkedConfig = mkOption {
         type = types.attrsOf types.nonEmptyStr;
+        default = {};
       };
     };
     groups =  mkOption {