Commentary (#4211) (#4254)

docs/CONTRIBUTORS

@@ -146,6 +146,7 @@ Stephen Henry
 Steven Hugg
 Sören Tempel
 Teng Huang
+Tim Hutt
 Tim Snyder
 Tobias Rosenkranz
 Tobias Wölfel

docs/guide/environment.rst

@@ -91,9 +91,29 @@ associated programs.
 
 .. option:: VERILATOR_ROOT
 
-   Specifies the directory containing the distribution kit.  This is used
-   to find the executable, Perl library, and include files.  If not
-   specified, it will come from a default optionally specified at configure
-   time (before Verilator was compiled).  It should not be specified if
-   using a pre-compiled Verilator package as the hard-coded value should be
-   correct.  See :ref:`Installation`.
+   The ``VERILATOR_ROOT`` environment variable is used in several places:
+
+   * At ``./configure`` time: If set, it is embedded into the binary, and
+     at runtime if ``VERILATOR_ROOT`` is not set, the embedded value is
+     used for the runtime default.
+
+   * When ``verilator`` is run: If ``VERILATOR_ROOT`` is set it will be
+     used to find the ``verilator_bin`` executable (this is the actual
+     Verilator binary; ``verilator`` is a Perl wrapper). If not set, the
+     ``verilator`` script uses other methods to find ``verilator_bin``
+     (looking in the same directory and falling back to ``$PATH``).
+
+   * When ``make`` is run on the Makefile generated by ``verilator``: The
+     value of ``VERILATOR_ROOT`` (falling back to the value embedded in the
+     binary if not set) is used to find the include files
+     (``include/verilated.mk``).
+
+   If you are using a pre-compiled Verilator package, you should not need
+   to set ``VERILATOR_ROOT`` - the value embedded in the binary should be
+   correct.  In fact this option *does not work* with Verilator packages
+   that have been installed with ``make install``. If a Verilator package
+   has been installed using ``./configure --prefix=/some/path && make
+   install`` and then moved to another location, you cannot use
+   ``VERILATOR_ROOT`` to point to the new version.
+
+   See :ref:`Installation` for more details.

docs/guide/install.rst

@@ -202,8 +202,9 @@ These are the installation options:
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Our personal favorite is to always run Verilator in-place from its Git
-directory. This allows the easiest experimentation and upgrading, and
-allows many versions of Verilator to co-exist on a system.
+directory (don't run ``make install``). This allows the easiest
+experimentation and upgrading, and allows many versions of Verilator to
+co-exist on a system.
 
 ::
 
@@ -212,10 +213,10 @@ allows many versions of Verilator to co-exist on a system.
    ./configure
    # Running will use files from $VERILATOR_ROOT, so no install needed
 
-Note after installing (below steps), a calling program or shell must set
-the environment variable :option:`VERILATOR_ROOT` to point to this Git
-directory, then execute ``$VERILATOR_ROOT/bin/verilator``, which will find
-the path to all needed files.
+Note after installing (see `Installation`_), a calling program or shell
+must set the environment variable :option:`VERILATOR_ROOT` to point to this
+Git directory, then execute ``$VERILATOR_ROOT/bin/verilator``, which will
+find the path to all needed files.
 
 
 2. Install into a specific location
@@ -233,7 +234,8 @@ location include the Verilator version name:
    # For the tarball, use the version number instead of git describe
    ./configure --prefix /CAD_DISK/verilator/`git describe | sed "s/verilator_//"`
 
-Note after installing (below steps), if you use `modulecmd
+Note after installing (see `Installation`_), you need to add the path to
+the ``bin`` directory to your ``PATH``. Or, if you use `modulecmd
 <http://modules.sourceforge.net/>`__, you'll want a module file like the
 following:
 
@@ -246,11 +248,11 @@ following:
    prepend-path PKG_CONFIG_PATH $install_root/share/pkgconfig
 
 
-3. Install into a Specific Path
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+3. Install into a Specific Prefix
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 You may eventually install Verilator into a specific installation prefix,
-as most GNU tools support:
+as follows. This option is typically only used by OS package maintainers.
 
 ::
 
@@ -274,8 +276,8 @@ configure's default system paths:
    unsetenv VERILATOR_ROOT   # if your shell is csh
    ./configure
 
-Then after installing (below), the binaries should be in a location
-already in your ``$PATH`` environment variable.
+Then after installing (see `Installation`_), the binaries should be in a
+location already in your ``$PATH`` environment variable.
 
 
 Configure