diff --git a/flake.nix b/flake.nix
index 74e1542..46affd4 100644
--- a/flake.nix
+++ b/flake.nix
@@ -13,7 +13,7 @@
         url = "https://static.rust-lang.org/dist/2021-01-29/channel-rust-nightly.toml";
         sha256 = "sha256-EZKgw89AH4vxaJpUHmIMzMW/80wAFQlfcxRoBD9nz0c=";
       };
-      targets = [];
+      rustTargets = [];
       rustChannelOfTargets = _channel: _date: targets:
         (pkgs.lib.rustLib.fromManifestFile rustManifest {
           inherit (pkgs) stdenv lib fetchurl patchelf;
@@ -21,7 +21,7 @@
           inherit targets;
           extensions = ["rust-src"];
         };
-      rust = rustChannelOfTargets "nightly" null targets;
+      rust = rustChannelOfTargets "nightly" null rustTargets;
       rustPlatform = pkgs.recurseIntoAttrs (pkgs.makeRustPlatform {
         rustc = rust;
         cargo = rust;
@@ -213,15 +213,65 @@
         doCheck = false;
         dontFixup = true;
       };
-    # ==== fsbl/
-    in {
-      packages.x86_64-linux = {
-        
-      };
+    # ==== fsbl/default
+    cargoSha256Experiments = "1bvffgr4588bbkjwnhim8rvkjvbnajaiv7hc98b19sr8kb7rcj63";
+    cargoSha256SZL = "13022ssk6s2fgxmmh5msbx01fzcmk2cj95fjpxcsmfy14k9wd77l";
 
-      hydraJobs = {
-        
-      };
+    build-crate = name: crate: features: cargoSha256: rustPlatform.buildRustPackage rec {
+      name = "${crate}";
+
+      src = builtins.filterSource (path: type:
+        baseNameOf path != "target"
+      ) ./.;
+      inherit cargoSha256;
+
+      nativeBuildInputs = [ cargo-xbuild pkgs.llvmPackages_9.clang-unwrapped ];
+      buildPhase = ''
+        export XARGO_RUST_SRC="${rustPlatform.rust.rustc}/lib/rustlib/src/rust/library"
+        export CARGO_HOME=$(mktemp -d cargo-home.XXX)
+        pushd ${crate}
+        cargo xbuild --release --frozen \
+          --no-default-features \
+          --features=${features}
+        popd
+      '';
+
+      installPhase = ''
+        mkdir -p $out $out/nix-support
+        cp target/armv7-none-eabihf/release/${name} $out/${name}.elf
+        echo file binary-dist $out/${name}.elf >> $out/nix-support/hydra-build-products
+      '';
+
+      doCheck = false;
+      dontFixup = true;
+    };
+
+    fsblCrates = {
+      zc706-fsbl = fsbl { board = "zc706"; };
+      # any others?
+    };
+
+    targetCrates = target: {
+      "${target}-experiments" = build-crate "${target}-experiments" "experiments" "target_${target}" cargoSha256Experiments;
+      "${target}-szl" = build-crate "${target}-szl" "szl" "target_${target}" cargoSha256SZL;
+    };
+    targets = ["zc706" "coraz7" "redpitaya" "kasli_soc"];
+    allTargetCrates = (builtins.foldl' (results: target:
+      results // targetCrates target
+    ) {} targets);
+    szl = pkgs.runCommand "szl" {} (builtins.foldl' (commands: target:
+      let
+        szlResult = builtins.getAttr "${target}-szl" allTargetCrates;
+      in
+        commands + "ln -s ${szlResult}/szl.elf $out/szl-${target}.elf\n"
+    ) "mkdir $out\n" targets);
+
+    allOutputs = allTargetCrates // fsblCrates // { inherit cargo-xbuild szl; };
+
+    in {
+      packages.x86_64-linux = allOutputs;
+
+      hydraJobs = allOutputs;
 
       devShell.x86_64-linux = pkgs.mkShell {
         name = "zynq-rs-dev-shell";
@@ -236,6 +286,6 @@
           llvmPackages_9.clang-unwrapped
           mkbootimage ];
         };
-      defaultPackage.x86_64-linux = fsbl { board = "zc706"; };
+      defaultPackage.x86_64-linux = allTargetCrates.zc706-szl;
     };
 }
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