Add nix develop support

docs/building-and-flashing/build.md

@@ -9,6 +9,9 @@ You'll need to use either the [Crazyflie VM](https://github.com/bitcraze/bitcraz
 [the toolbelt](https://github.com/bitcraze/toolbelt) or
 install some ARM toolchain.
 
+There is also experimental support for [building with nix](./nix.md).
+This allows to build the firmware in a reproducable way.
+
 ### Install a toolchain
 
 #### Toolchain and compiler version policy

docs/building-and-flashing/nix.md

@@ -0,0 +1,29 @@
+---
+title: Building using nix
+page_id: nix
+---
+
+The [Nix package manager](https://nixos.org) can be used to build the firmware in a reliable way without having to install all the dependencies on your system.
+All that is needed is to have the nix package manager installed with [Flake support enabled](https://nixos.wiki/wiki/flakes).
+The easiest if nix is not installed yet is to install it from [zero to Nix](https://zero-to-nix.com/start/install/).
+Nix support in this project is currently experimental.
+
+## Development shell
+
+To get into a development shell where required tools for building the project are present:
+
+``` bash
+nix develop
+```
+
+## Building with Nix
+
+The following command will produce a clean build for the Crazyflie 2. The command can be changed to build for other target:
+
+``` bash
+nix develop -i --command bash -c 'make mrproper && make cf2_defconfig && make -j`nproc`'
+```
+
+## Updating the flake
+
+One great advantage of working with Nix is that the versions are locked in the `nix.lock` file. This means that build are reproducable. Running `nix flake update` can be used to update dependencies. The file `nix.lock` then need to be commited and pushed.

flake.nix

@@ -0,0 +1,32 @@
+{
+  description = "Crazyflie firmware development environment";
+
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
+  };
+
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem
+    (
+      system: let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in {
+        formatter = pkgs.alejandra;
+
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = with pkgs; [
+            gcc
+            gnumake
+            gcc-arm-embedded
+            python3
+            git
+          ];
+        };
+      }
+    );
+}

tools/kbuild/Makefile.kbuild

@@ -137,7 +137,7 @@ ifneq ($(KBUILD_OUTPUT),)
 # check that the output directory actually exists
 saved-output := $(KBUILD_OUTPUT)
 KBUILD_OUTPUT := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) \
-								&& /bin/pwd)
+								&& pwd)
 $(if $(KBUILD_OUTPUT),, \
      $(error failed to create output directory "$(saved-output)"))