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

Addresses item 2. of Gitea issue #1.

artiq-fast/artiq-board.nix

@@ -8,6 +8,9 @@
 , extraInstallCommands ? ""}:
 
 let
+  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}";
   artiqSrc = import ./pkgs/artiq-src.nix { fetchgit = pkgs.fetchgit; };
   fetchcargo = import ./fetchcargo.nix {
     inherit (pkgs) stdenv cacert git cargo cargo-vendor;
@@ -47,13 +50,13 @@ let
 
   # Board packages are Python modules so that they get added to the ARTIQ Python
   # environment, and artiq_flash finds them.
-in pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation rec {
-  name = "artiq-board-${target}-${variant}-${version}";
-  version = import ./pkgs/artiq-version.nix (with pkgs; { inherit stdenv fetchgit git; });
+  boardModule = pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation {
+    name = "${name}-firmware";
+    inherit version;
     phases = [ "buildPhase" "installCheckPhase" "installPhase" ];
     buildInputs = [
       vivado
-    pkgs.gnumake
+      pkgs.gnumake pkgs.which
       (pkgs.python3.withPackages(ps: with ps; [ jinja2 numpy artiqpkgs.migen artiqpkgs.microscope artiqpkgs.misoc artiqpkgs.jesd204b artiqpkgs.artiq ]))
       pkgs.cargo
       artiqpkgs.rustc
@@ -64,27 +67,33 @@ in pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation rec {
       ''
       export CARGO_HOME=${cargoVendored}
       export TARGET_AR=or1k-linux-ar
-    ${buildCommand}
-    '';
-  checkPhase = ''
-    # Search for PCREs in the Vivado output to check for errors
-    check_log() {
-      set +e
-      grep -Pe "$1" artiq_${target}/${variant}/gateware/vivado.log
-      FOUND=$?
-      set -e
-      if [ $FOUND != 1 ]; then
-        exit 1
-      fi
-    }
-    check_log "\d+ constraint not met\."
-    check_log "Timing constraints are not met\."
+      ${buildCommand} --no-compile-gateware
       '';
     installPhase =
       ''
-    TARGET_DIR=$out/${pkgs.python3Packages.python.sitePackages}/artiq/board-support/${target}-${variant}
-    mkdir -p $TARGET_DIR
-    cp artiq_${target}/${variant}/gateware/top.bit $TARGET_DIR
+      TARGET_DIR=$out/${installPath}
+      mkdir -p $TARGET_DIR $out/src
+
+      cp -ar artiq_${target}/${variant}/gateware $out/src/
+      pushd $out/src/gateware
+      LIB_PATH=$(dirname $(dirname $(which python)))/${pkgs.python3Packages.python.sitePackages}
+      (
+        set -e
+        cd $LIB_PATH
+        for EXT in v vh
+        do
+          find misoc/ -name "*.$EXT" -type f
+        done
+      ) | while read V
+      do
+        SRC=$LIB_PATH/$V
+        mkdir -p $(dirname $V)
+        cp $SRC $V
+        substituteInPlace top.tcl --replace $SRC $V \
+          2> /dev/null
+      done
+      popd
+
       if [ -e artiq_${target}/${variant}/software/bootloader/bootloader.bin ]
       then cp artiq_${target}/${variant}/software/bootloader/bootloader.bin $TARGET_DIR
       fi
@@ -94,4 +103,60 @@ in pkgs.python3Packages.toPythonModule (pkgs.stdenv.mkDerivation rec {
       fi
       ${extraInstallCommands}
       '';
-})
+  });
+
+  gatewareSourceArchive = pkgs.stdenv.mkDerivation {
+    name = "${name}-gateware-source.nar.base64";
+    buildInputs = [ pkgs.nix ];
+    phases = [ "installPhase" ];
+    installPhase = "nix-store --dump ${boardModule}/src/gateware | base64 -w0 > $out";
+  };
+
+  # Funnelling the source code through a Nix string allows dropping
+  # all dependencies via `unsafeDiscardStringContext`. The gateware
+  # will then be rebuilt only when these contents have changed.
+  pureGatewareSourceArchive = builtins.toFile "${name}-gateware-source.nar.base64" (
+    builtins.unsafeDiscardStringContext (
+      builtins.readFile gatewareSourceArchive
+    ));
+
+  # Depends on just Vivado and the generated Bitstream source
+  gateware = pkgs.stdenvNoCC.mkDerivation {
+    name = builtins.unsafeDiscardStringContext "${name}-gateware";
+
+    unpackPhase = "base64 -d < ${pureGatewareSourceArchive} | nix-store --restore gateware";
+    buildInputs = [ vivado pkgs.nix ];
+    buildPhase = ''
+      cd gateware
+      vivado -mode batch -source top.tcl
+    '';
+
+    installPhase = ''
+      TARGET_DIR=$out/${builtins.unsafeDiscardStringContext installPath}
+      mkdir -p $TARGET_DIR
+
+      chmod a+r top.bit
+      cp top.bit $TARGET_DIR
+    '';
+
+    doCheck = true;
+    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 [ $FOUND != 1 ]; then
+          exit 1
+        fi
+      }
+      check_log "\d+ constraint not met\."
+      check_log "Timing constraints are not met\."
+    '';
+  };
+in pkgs.buildEnv rec {
+  inherit name;
+  paths = [ boardModule gateware ];
+  pathsToLink = [ "/${installPath}" ];
+}