artiq-fast: build gateware from a self-contained separate source derivation

Addresses item 2. of Gitea issue #1.

artiq-fast/artiq-board.nix

@@ -6,6 +6,7 @@
 }:
 
 let
+  version = import ./pkgs/artiq-version.nix (with pkgs; { inherit stdenv fetchgit git; });
   artiqSrc = import ./pkgs/artiq-src.nix { fetchgit = pkgs.fetchgit; };
   artiqpkgs = import ./default.nix { inherit pkgs; };
   fetchcargo = import ./fetchcargo.nix {
@@ -41,52 +42,47 @@ let
       cp -R * $out/registry
       '';
   };
-
 in
 { target
 , variant
 , src ? null
 , buildCommand ? "python -m artiq.gateware.targets.${target} -V ${variant}"
 , extraInstallCommands ? ""}:
-
+let
-# Board packages are Python modules so that they get added to the ARTIQ Python
-# environment, and artiq_flash finds them.
-pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation rec {
   name = "artiq-board-${target}-${variant}-${version}";
-  version = import ./pkgs/artiq-version.nix (with pkgs; { inherit stdenv fetchgit git; });
+  installPath = "${pkgs.python3Packages.python.sitePackages}/artiq/board-support/${target}-${variant}";
-  inherit src;
+
+  boardModule = 
+    # Board packages are Python modules so that they get added to the ARTIQ Python
+    # environment, and artiq_flash finds them.
+    pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation {
+      name = "${name}-firmware";
+      inherit version src;
       phases = [ "buildPhase" "installCheckPhase" "installPhase" "checkPhase" ];
       nativeBuildInputs = [
         vivado
-    pkgs.gnumake
+        pkgs.gnumake pkgs.which
         artiqpkgs.cargo
         artiqpkgs.rustc
         artiqpkgs.binutils-or1k
         artiqpkgs.llvm-or1k
       ];
-  buildInputs = [ (pkgs.python3.withPackages(ps: with ps; [ jinja2 numpy artiqpkgs.migen artiqpkgs.microscope artiqpkgs.misoc artiqpkgs.jesd204b artiqpkgs.artiq ])) ];
+      buildInputs = [
+        (pkgs.python3.withPackages(ps: with ps; [ jinja2 numpy artiqpkgs.migen artiqpkgs.microscope artiqpkgs.misoc artiqpkgs.jesd204b artiqpkgs.artiq ]))
+      ];
       buildPhase =
         ''
         export CARGO_HOME=${cargoVendored}
         export TARGET_AR=or1k-linux-ar
-    ${buildCommand}
+        ${buildCommand} --no-compile-gateware
-    '';
-  # temporarily disabled because there is currently always at least one Kasli bitstream
-  # that fails timing and blocks the conda channel.
-  doCheck = false;
-  checkPhase = ''
-    # Search for PCREs in the Vivado output to check for errors
-    check_log() {
-      grep -Pe "$1" artiq_${target}/${variant}/gateware/vivado.log && exit 1 || true
-    }
-    check_log "\d+ constraint not met\."
-    check_log "Timing constraints are not met\."
         '';
       installPhase =
         ''
-    TARGET_DIR=$out/${pkgs.python3Packages.python.sitePackages}/artiq/board-support/${target}-${variant}
+        TARGET_DIR=$out/${installPath}
-    mkdir -p $TARGET_DIR
+        mkdir -p $TARGET_DIR $out/src
-    cp artiq_${target}/${variant}/gateware/top.bit $TARGET_DIR
+
+        cp -ar artiq_${target}/${variant}/gateware $out/src/
+
         if [ -e artiq_${target}/${variant}/software/bootloader/bootloader.bin ]
         then cp artiq_${target}/${variant}/software/bootloader/bootloader.bin $TARGET_DIR
         fi
@@ -96,4 +92,62 @@ pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation rec {
         fi
         ${extraInstallCommands}
         '';
-})
+    });
+
+  vivadoInputArchive = pkgs.stdenv.mkDerivation {
+    name = "${name}-vivado-input.nar.base64";
+    buildInputs = [ pkgs.nix ];
+    phases = [ "installPhase" ];
+    installPhase = "nix-store --dump ${boardModule}/src/gateware | base64 -w0 > $out";
+  };
+
+  # Funnelling the source code through a Nix string allows dropping
+  # all dependencies via `unsafeDiscardStringContext`. The gateware
+  # will then be rebuilt only when these contents have changed.
+  pureVivadoInputArchive = builtins.toFile "${name}-vivado-input.nar.base64" (
+    builtins.unsafeDiscardStringContext (
+      builtins.readFile vivadoInputArchive
+    ));
+
+  # Depends on just Vivado and the generated Bitstream source
+  vivadoOutput = pkgs.stdenvNoCC.mkDerivation {
+    name = builtins.unsafeDiscardStringContext "${name}-vivado-output";
+
+    unpackPhase = "base64 -d < ${pureVivadoInputArchive} | nix-store --restore gateware";
+    buildInputs = [ vivado pkgs.nix ];
+    buildPhase = ''
+      cd gateware
+      vivado -mode batch -source top.tcl
+    '';
+
+    installPhase = ''
+      TARGET_DIR=$out/${builtins.unsafeDiscardStringContext installPath}
+      mkdir -p $TARGET_DIR
+
+      chmod a+r top.bit
+      cp top.bit $TARGET_DIR
+    '';
+
+    # temporarily disabled because there is currently always at least one Kasli bitstream
+    # that fails timing and blocks the conda channel.
+    doCheck = false;
+    checkPhase = ''
+      # Search for PCREs in the Vivado output to check for errors
+      check_log() {
+        set +e
+        grep -Pe "$1" vivado.log
+        FOUND=$?
+        set -e
+        if [ $FOUND != 1 ]; then
+          exit 1
+        fi
+      }
+      check_log "\d+ constraint not met\."
+      check_log "Timing constraints are not met\."
+    '';
+  };
+in pkgs.buildEnv rec {
+  inherit name;
+  paths = [ boardModule vivadoOutput ];
+  pathsToLink = [ "/${installPath}" ];
+}