add nix files

default.nix

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+{ # Use master branch of the overlay by default
+  mozillaOverlay ? import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz),
+}:
+
+let
+  pkgs = import <nixpkgs> { overlays = [ mozillaOverlay ]; };
+in
+with pkgs;
+let
+  rustcSrc = fetchgit {
+    url = https://github.com/rust-lang/rust.git;
+    # master of 2019-08-18
+    rev = "ea52be482ab4945fda63cb65b6a198309a041e3c";
+    sha256 = "1spifrkvyyrh1gazqrby29fjqsdbwvajv9k9f6mk2ldrdghlsd21";
+    fetchSubmodules = true;
+  };
+  targets = [
+  ];
+  rust =
+    rustChannelOfTargets "nightly" null targets;
+  rustPlatform = recurseIntoAttrs (makeRustPlatform {
+    rustc = rust // { src = rustcSrc; };
+    cargo = rust;
+  });
+in {
+  inherit pkgs rustPlatform rustcSrc;
+}

shell.nix

@@ -0,0 +1,25 @@
+let
+  mozillaOverlay = import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz);
+  pkgs = import <nixpkgs> { overlays = [ mozillaOverlay ]; };
+in
+with pkgs;
+let
+  project = callPackage ./default.nix {};
+in
+with project;
+stdenv.mkDerivation {
+  name = "armdev-env";
+  buildInputs = with rustPlatform.rust; [
+    rustc cargo cargo-xbuild
+    rustcSrc
+    openocd
+  ];
+
+  # Set Environment Variables
+  RUST_BACKTRACE = 1;
+  XARGO_RUST_SRC = "${rustcSrc}/src";
+
+  shellHook = ''
+    echo "Run 'cargo xbuild --release' to build."
+  '';
+}