[doc] add tcl api

docs/source/dev_manual/index.rst

@@ -12,3 +12,5 @@
 
    regression_tests
 
+   tcl_api
+

docs/source/dev_manual/tcl_api.rst

@@ -0,0 +1,33 @@
+.. _dev_manual_tcl_api:
+
+Tcl API
+-------
+
+OpenFPGA can be loaded to a Tcl shell in the format of shared library.
+OpenFPGA's Tcl APIs are generated by SWIG during compilation. 
+By integrating OpenFPGA to Tcl, developers can utilize OpenFPGA commands in a common shell with other EDA tools, considering most of modern EDA tools adopt Tcl as their user interface.
+Currently, Tcl 8.6 is supported. Other versions may also work.
+
+Here are the steps to follow:
+
+- Compile OpenFPGA with SWIG enabled. See details in :ref:`tutorial_compile`.
+- The shared library of OpenFPGA is available under the ``build/openfpga/openfpgashell.so``
+- Launch a tcl shell and load the shared library. For example
+
+.. code-block::
+
+  load openfpga_shell.so
+
+- Create a new OpenFPGA shell object. For example
+
+.. code-block::
+
+  std::OpenfpgaShell my_shell
+
+- OpenFPGA command can be called by through a sub command ``run_command``. For example, the command ``read_openfpga_arch`` (see :ref:`openfpga_setup_commands` for details) is now run in the following way: 
+
+.. code-block::
+
+  my_shell run_command "read_openfpga_arch --file ~/OpenFPGA/openfpga_flow/openfpga_arch/k4_N4_40nm_bank_openfpga.xml" 
+
+