[syn] Add nix devShell for example synthesis flow

Provide a .#syn_shell development environment in which the sample synthesis flow
using yosys can be executed. This shell provisions the nangate45 PDK into the
nix store and sets an environment variable pointing to it which is picked up by
the synthesis scripts.

A quick-start for how to use this shell is added to the syn/README.

Signed-off-by: Harry Callahan <hcallahan@lowrisc.org>

Author: hcallahan-lowrisc

flake.nix

@@ -65,6 +65,12 @@
       url = "github:nix-community/fenix";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+
+    # Deps for synthesis flows
+    sv2v = {
+      url = "github:zachjs/sv2v";
+      flake = false;
+    };
   };
 
   # The lowRISC public nix-cache contains builds of nix packages used by lowRISC, primarily coming from github:lowRISC/lowrisc-nix.
@@ -86,6 +92,10 @@
       let
         pkgs = import inputs.nixpkgs {
           inherit system;
+          config = {
+            allowUnfree = true;
+            allowBroken = true; # sv2v marked as broken.
+          };
         };
         inherit (pkgs) lib;
 
@@ -160,6 +170,8 @@
             mypy
           ]);
 
+        ibex_syn = import ./nix/syn.nix {inherit inputs pkgs;};
+
         # lowRISC fork of the Sail repository. The SAIL -> SV flow is used to generate the reference model.
         lowrisc_sail = import ./nix/lowrisc_sail.nix {
           inherit pkgs;
@@ -297,6 +309,12 @@
           '';
         };
 
+        syn_shell = shell.override (prev: {
+          name = "ibex-devshell-synthesis";
+          nativeBuildInputs = prev.nativeBuildInputs ++ ibex_syn.deps;
+          shellHook = prev.shellHook + ibex_syn.profile;
+        });
+
         # This shell uses mkShellNoCC as the stdenv CC can interfere with EDA tools.
         eda_shell = pkgs.lib.makeOverridable pkgs.mkShellNoCC {
           name = "ibex-devshell-eda";
@@ -320,7 +338,7 @@
             inherit lowrisc_sail;
           };
           devShells = rec {
-            inherit shell eda_shell;
+            inherit shell syn_shell eda_shell;
             formal = mkshell-minimal {
               packages = standard_deps;
               shellHook = check_jg + exports;

nix/sv2v.nix

@@ -0,0 +1,34 @@
+# Copyright lowRISC Contributors.
+# Licensed under the MIT License, see LICENSE for details.
+# SPDX-License-Identifier: MIT
+
+# Taken from:
+# https://github.com/deemp/gists/blob/master/haskellPackage/flake.nix
+
+{
+  inputs,
+  pkgs,
+  ...
+}: let
+  packageName = "sv2v";
+  ghcVersion = "928";
+
+  inherit (pkgs.haskell.lib) overrideCabal justStaticExecutables;
+  hpkgs = pkgs.haskell.packages."ghc${ghcVersion}";
+
+  # executableToolDepends - from "sv2v" expression in https://raw.githubusercontent.com/NixOS/nixpkgs/nixos-unstable/pkgs/development/haskell-modules/hackage-packages.nix
+  package = overrideCabal (hpkgs.callCabal2nix packageName inputs.sv2v.outPath { })
+    (x: {
+      executableToolDepends = (x.executableToolDepends or [ ]) ++ (
+        # Add the following extra dependencies
+        with pkgs; [
+          alex
+          happy
+        ]
+      );
+    });
+
+in {
+  default = justStaticExecutables package;
+  inherit package;
+}

nix/syn.nix

@@ -0,0 +1,52 @@
+# Copyright lowRISC Contributors.
+# Licensed under the MIT License, see LICENSE for details.
+# SPDX-License-Identifier: MIT
+
+# Deps for Ibex synthesis jobs
+
+{
+  inputs,
+  pkgs,
+  ...
+}: let
+
+  sv2v_local = import ./sv2v.nix {inherit inputs pkgs;};
+
+  ibex_syn_deps = [
+    sv2v_local.default
+  ] ++ (with pkgs; [
+    # haskellPackages.sv2v # broken
+    yosys
+    openroad
+  ]);
+
+  # Create a dumb package of nangate45
+  # > All we need is a path to the sources
+  nangate45 = pkgs.stdenv.mkDerivation rec {
+    pname = "openroad-nangate45";
+    version = "PDKv1.3_v2010_12.Apache.CCL";
+    src = pkgs.fetchFromGitHub {
+      owner = "The-OpenROAD-Project";
+      repo = "OpenROAD-flow-scripts";
+      rev = "181e9133776117ea1b9f74dbacbfdaadff8c331b"; # Tag: v3.0
+      hash = "sha256-fYAdhBsMcuCXmPMQVCRdm75Tk0rd9zLnLfJdjhnhC00=";
+    };
+    sourceRoot = "${src.name}/flow/platforms/nangate45";
+    phases = [ "unpackPhase" "installPhase" ];
+    installPhase = ''
+        mkdir -p $out
+        cp -r ./* $out
+      '';
+  };
+
+  ibex_syn_profile = ''
+    export LR_SYNTH_CELL_LIBRARY_NAME=nangate
+    export LR_SYNTH_CELL_LIBRARY_PATH=${nangate45}/lib/NangateOpenCellLibrary_typical.lib
+  '';
+
+in {
+
+  deps = ibex_syn_deps;
+  profile = ibex_syn_profile;
+
+}

syn/README.md

@@ -2,6 +2,23 @@
 tape-out quality netlists and area/timing numbers it generates are not
 representative of what would be achievable with a tape-out quality flow**
 
+# Quick start with Nix
+
+If you have Nix with flakes enabled, all dependencies and the Nangate45 cell
+library are provided automatically via the `syn_shell` devShell. Enter the
+shell and run the flow:
+
+```sh
+nix develop .#syn_shell
+cd syn
+./syn_yosys.sh
+```
+
+No further setup is needed — `syn_setup.sh` is pre-configured and
+`LR_SYNTH_CELL_LIBRARY_PATH`/`LR_SYNTH_CELL_LIBRARY_NAME` are exported by the
+shell hook. The remaining sections describe manual installation for non-Nix
+environments.
+
 # Yosys/OpenSTA Ibex Synthesis Flow
 
 This is a synthesis-only implementation flow using Yosys for Synthesis and
@@ -39,13 +56,14 @@ format. The following Open Libraries can be used:
 
 # Synthesis flow setup
 
-The synthesis flow is configured via environment variables. The `syn_setup.sh`
-file is used to set the environment variables for the flow and any changes made
-should be placed there.  An example `syn_setup.example.sh` is included. A copy
-of this named `syn_setup.sh` must be made and the values in it set appropriately
-for the flow to work.
+The synthesis flow is configured via environment variables. `syn_setup.sh` sets
+the environment variables for the flow.
+
+When using `nix develop .#syn_shell`, the cell library variables below are
+exported automatically by the shell hook and no edits to `syn_setup.sh` are
+needed. For non-Nix environments, set them manually in `syn_setup.sh`.
 
-The environment variables that must be set in `syn_setup.sh` are
+The environment variables that must be set are:
 
 * `LR_SYNTH_CELL_LIBRARY_PATH` - The path to the standard cell library, this
   should point to the absolute path of the Nangate45 library
@@ -56,7 +74,7 @@ The environment variables that must be set in `syn_setup.sh` are
 
 # Running the synthesis flow
 
-Once `syn_setup.sh` has been created, call `syn_yosys.sh` to run the entire
+Once the environment is configured, call `syn_yosys.sh` to run the entire
 flow. All outputs are placed under the `syn/syn_out` directory with the prefix
 `ibex_` with the current date/time forming the rest of the name, e.g.
 `syn/syn_out/ibex_06_01_2020_11_19_15`

syn/syn_setup.example.sh syn/syn_setup.shsyn/syn_setup.example.sh renamed to syn/syn_setup.sh

@@ -18,7 +18,10 @@ fi
 export LR_SYNTH_TIMING_RUN=1
 export LR_SYNTH_FLATTEN=1
 
-# SETUP CELL LIBRARY PATH
-# Uncomment the lines below and set the path to an appropriate .lib file
+# When using `nix develop .#syn_shell`, the following are set automatically by
+# the shell hook (via nix/syn.nix):
+#   LR_SYNTH_CELL_LIBRARY_PATH  (path to NangateOpenCellLibrary_typical.lib)
+#   LR_SYNTH_CELL_LIBRARY_NAME  (nangate)
+# For non-Nix environments, uncomment and set these manually:
 # export LR_SYNTH_CELL_LIBRARY_PATH=/path/to/NangateOpenCellLibrary_typical.lib
 # export LR_SYNTH_CELL_LIBRARY_NAME=nangate