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-rw-r--r--bsp-howto/clock.rst12
1 files changed, 8 insertions, 4 deletions
diff --git a/bsp-howto/clock.rst b/bsp-howto/clock.rst
index 55c94ac..efe9fad 100644
--- a/bsp-howto/clock.rst
+++ b/bsp-howto/clock.rst
@@ -269,12 +269,16 @@ The hardware-specific support at tick is specified by
System Shutdown Support
=======================
-The :dfn:`Clock Driver Shell` provides the routine ``Clock_exit()`` that is
-scheduled to be run during system shutdown via the ``atexit()`` routine. The
-hardware-specific shutdown support is specified by
+Optionally, the :dfn:`Clock Driver Shell` provides the routine ``Clock_exit()``
+that is scheduled to be run during system shutdown via the ``atexit()``
+routine. The hardware-specific shutdown support is specified by
``Clock_driver_support_shutdown_hardware()`` which is used by ``Clock_exit()``.
It should disable the clock tick source if it was enabled. This can be used to
-prevent clock ticks after the system is shutdown.
+prevent clock ticks after the system is shutdown. The
+``Clock_driver_support_shutdown_hardware()`` must be provided as a macro. In
+case this macro is undefined, then the shutdown support is disabled. This is
+useful for example on memory constrained systems to avoid the ``atexit()``
+overhead.
.. code-block:: c