doc: document --synth command.

1 files changed, 29 insertions, 0 deletions

diff --git a/doc/using/InvokingGHDL.rst b/doc/using/InvokingGHDL.rst
index bea132d60..a2099152c 100644
--- a/doc/using/InvokingGHDL.rst
+++ b/doc/using/InvokingGHDL.rst
@@ -227,6 +227,35 @@ Theses rules can then be integrated in another Makefile.
 
 .. _GHDL:options:
 
+Synthesis command
+=================
+
+GHDL supports synthesis, but only as a front-end: it generates a
+generic netlist that is not optimized.
+
+.. index:: synthesis command
+
+.. _Synth:command:
+
+Synthesis [``--synth``]
+-----------------------
+
+.. option:: --synth <[options] [unit]>
+
+.. option:: --synth <[options] files -e [unit]>
+
+The first command elaborates for synthesis the design whose top unit
+is indicated by ``unit``.  All the units must have been analyzed.  The
+second form analyze only the files present on the command line and
+then elaborate them starting from the top ``unit``.  A generic netlist
+is then displayed using a very simple vhdl subset.
+
+The command line is the same as the ``ghdl`` command added to
+Yosys by the ghdl plugin except ``--synth`` is not present.  With this
+plugin, it is possible to optimize and map to a target the netlist.
+
+This command is useful for checking that a design could be synthesized.
+
 Options
 =======