add moondancer firmware

pkgs/cynthion/moondancer.nix

@@ -0,0 +1,42 @@
+{
+  makeRustPlatform,
+  rustc,
+  cynthion-unwrapped,
+  zsh,
+  yosys,
+  nextpnr,
+  trellis,
+  rust-bin,
+  pkgsCross,
+  ...
+}: let
+  # this doesn't work yet...
+  toolchain = rust-bin.stable.${rustc.version}.default.override {
+    extensions = ["rust-src"];
+    targets = ["riscv32imac-unknown-none-elf"];
+  };
+  rustPlatform = pkgsCross.riscv32-embedded.pkgsBuildHost.makeRustPlatform {
+    cargo = toolchain;
+    rustc = toolchain;
+  };
+in
+  rustPlatform.buildRustPackage rec {
+    pname = "cynthion-moondancer";
+    inherit (cynthion-unwrapped) version src;
+
+    postPatch = ''
+      cp ${./moondancer-cargo.lock} Cargo.lock
+
+      substituteInPlace Cargo.toml \
+              --replace-fail '[profile.release]' "[profile.release]
+              panic=\"abort\""
+    '';
+
+    cargoLock = {
+      lockFile = ./moondancer-cargo.lock;
+    };
+
+    sourceRoot = "source/firmware";
+
+    cargoBuildFlags = ["-p moondancer" "--target riscv32imac-unknown-none-elf"];
+  }