start of a hal crate

flake.nix

@@ -0,0 +1,66 @@
+{
+  description = "STM32U575ZI-Q Rust Embedded Development Environment";
+
+  inputs = { nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable"; };
+
+  outputs = { self, nixpkgs }: let
+    system = "x86_64-linux";
+    pkgs = import nixpkgs { inherit system; };
+  in {
+    devShells.${system}.default = pkgs.mkShell {
+      packages = with pkgs; [
+        # Base toolchain
+        rustup
+        llvm
+        gcc
+        gnumake
+        cmake
+        pkg-config
+        python3
+        git
+        curl
+        wget
+        unzip
+
+        # ARM embedded cross toolchain
+        gcc-arm-embedded
+
+        # Flashing / Debug
+        openocd
+        probe-rs
+        cargo-binutils
+        cargo-generate
+        flip-link
+      ];
+
+      shellHook = ''
+        echo ">>> STM32U575ZI-Q Rust (HAL + PAC) DevShell"
+        echo "---------------------------------------------"
+
+        # Set up Rust target
+        rustup target add thumbv7em-none-eabihf 2>/dev/null || true
+
+        # Ensure probe-rs binary is in PATH
+        if ! command -v probe-rs >/dev/null; then
+          echo "⚠️ probe-rs not found! (check nix installation)"
+        fi
+
+        export RUST_TARGET=thumbv7em-none-eabihf
+        export CARGO_TARGET_DIR=target
+        export PATH=$PATH:${pkgs.gcc-arm-embedded}/bin
+
+        echo "🧩 Target: $RUST_TARGET"
+        echo "💡 Examples:"
+        echo "  1️⃣  cargo generate --git https://github.com/rust-embedded/cortex-m-quickstart --name stm32u5-blinky"
+        echo "  2️⃣  cd stm32u5-blinky && cargo build --release --target thumbv7em-none-eabihf"
+        echo "  3️⃣  probe-rs run --chip STM32U575ZITxQ target/thumbv7em-none-eabihf/release/stm32u5-blinky"
+        echo ""
+        echo "🧠 TIP: Add stm32u5xx-hal to Cargo.toml to access register-level HAL API."
+        echo "---------------------------------------------"
+
+        rustc --version
+        arm-none-eabi-gcc --version | head -n1
+      '';
+    };
+  };
+}