diff --git a/docs/source/manual/openfpga_shell/openfpga_commands/setup_commands.rst b/docs/source/manual/openfpga_shell/openfpga_commands/setup_commands.rst
index ea2a20723..2bf9e4ccb 100644
--- a/docs/source/manual/openfpga_shell/openfpga_commands/setup_commands.rst
+++ b/docs/source/manual/openfpga_shell/openfpga_commands/setup_commands.rst
@@ -130,8 +130,17 @@ Clock signals will be auto-detected and routed based on pin constraints which ar
 
   .. option:: --pin_constraints_file <string> or -pcf <string>
 
-    Specify the *Pin Constraints File* (PCF) when the clock network contains multiple clock pins. For example, ``-pin_constraints_file pin_constraints.xml``
-    Strongly recommend for multi-clock network. See detailed file format about :ref:`file_format_pin_constraints_file`.
+    Specify the *Pin Constraints File* (PCF) when the clock network contains multiple clock pins. For example, ``-pin_constraints_file pin_constraints.xml``. Strongly recommend for multi-clock network. See detailed file format about :ref:`file_format_pin_constraints_file`.
+
+.. note:: If there is a global net, e.g., ``clk`` or ``reset``, which will be driven by an internal resource, it should also be defined in the PCF file.
+
+  .. option:: --disable_unused_trees
+
+    Disable entire clock trees when they are not used by any clock nets. Useful to reduce clock power
+
+  .. option:: --disable_unused_spines
+ 
+    Disable part of the clock tree which are used by clock nets. Useful to reduce clock power
 
   .. option:: --verbose