nuttx/Documentation/quickstart/debugging.rst

.. include:: /substitutions.rst
.. _debugging:

Debugging
=========

Finding and fixing bugs is an important part of the hardware and software development process. Sometimes you also need
to use debugging techniques to understand how the system works. Two tools that are helpful are debug logging and
debugging using the GNU Debugger (gdb).

Debug Logging
-------------

NuttX has a powerful system logging facility (syslog) with ``info``, ``warn``, and ``error`` levels. You can enable
debugging for your build for the subsystem or feature by using the ``menuconfig`` system.

.. code-block:: console

   $ make menuconfig

The debug options are available under ``Build Setup`` > ``Debug Options``. You will most likely have to enable the
following options:

* ``Enable Debug Features`` — selecting this will turn on subsystem-level debugging options, they will become visible
  on the page below. You can then select the ones you want.
* ``Enable Error Output`` — this will only log errors.
* ``Enable Warnings Output`` — this will log warnings and errors.
* ``Enable Informational Debug Output`` — this will produce informational output, warnings, and errors.

You can then select from the subsystems that are available, Network, Scheduler, USB, etc. Note that you will need to
separately enable the subsystem elsewhere in the ``menuconfig`` system. To see the ``CONFIG`` define that is set,
use the arrow keys to highlight the subsystem (for instance, ``Network Debug Features``) and type '?'. This will show
you that the C macro that is set is called ``CONFIG_DEBUG_NET``. ``debug.h`` defines the ``netinfo()`` logging
function that will log output if this macro is set. You can search the source code for ``netinfo`` to see how it is
used.

.. image:: ../_static/images/menuconfig-debug.png
    :width: 800px
    :align: center
    :alt: Screenshot of menuconfig system main screen

Note that enabling all these will produce an incredible amount of logging output. Enable the level you want and
the area you're interested in, and leave the rest disabled, save the config, and then recompile. You can see the full
list of debug feature logging functions in the file
`debug.h <https://github.com/apache/incubator-nuttx/blob/master/include/debug.h>`__.

Syslog timestamps can be enabled in the ``menuconfig`` system using ``Device Drivers`` > ``System Logging`` > ``Prepend
timestamp to syslog message`` (``CONFIG_SYSLOG_TIMESTAMP``).

You may need to do a little bit of experimenting to find the combination of logging settings that work for the problem
you're trying to solve. See the file `debug.h <https://github.com/apache/incubator-nuttx/blob/master/include/debug.h>`_
for available debug settings that are available. This can also be configured via the ``menuconfig`` system.

There are also subsystems that enable USB trace debugging, and you can log to memory too, if you need the logging to be
faster than what the console can output.

Changing Debug Settings Quickly
-------------------------------

You can use the ``kconfig-tweak`` script that comes with the ``kconfig-frontends`` tools to quickly change debug settings,
for instance turning them on or off before doing a build:

.. code-block:: console

   $ kconfig-tweak --disable CONFIG_DEBUG_NET
   $ make olddefconfig  # needed to have the kconfig system check the config
   $ kconfig-tweak --enable CONFIG_DEBUG_NET
   $ make olddefconfig

You can put a bunch of these into a simple script to configure the logging the way you want:

.. code-block:: console

   #!/bin/bash

   kconfig-tweak --disable CONFIG_DEBUG_ALERT
   kconfig-tweak --disable CONFIG_DEBUG_FEATURES
   kconfig-tweak --disable CONFIG_DEBUG_ERROR
   kconfig-tweak --disable CONFIG_DEBUG_WARN
   kconfig-tweak --disable CONFIG_DEBUG_INFO
   kconfig-tweak --disable CONFIG_DEBUG_ASSERTIONS
   kconfig-tweak --disable CONFIG_DEBUG_NET
   kconfig-tweak --disable CONFIG_DEBUG_NET_ERROR
   kconfig-tweak --disable CONFIG_DEBUG_NET_WARN
   kconfig-tweak --disable CONFIG_DEBUG_NET_INFO
   kconfig-tweak --disable CONFIG_DEBUG_SYMBOLS
   kconfig-tweak --disable CONFIG_DEBUG_NOOPT
   kconfig-tweak --disable CONFIG_SYSLOG_TIMESTAMP
   make oldconfig


JTAG Debugging
--------------

`JTAG <https://en.wikipedia.org/wiki/JTAG>`_ is a set of standards that specify a way to attach a hardware device to
your embedded board, and then remotely control the CPU. You can load code, start, stop, step through the program, and
examine variables and memory.

This guide assumes your board has a JTAG connector, and you have a JTAG hardware debugger like a
`Segger J-Link <https://www.segger.com/products/debug-probes/j-link/>`_ or `OpenOCD <http://openocd.org/doc-release/html/index.html>`_.

The NuttX operating system uses `threads <https://en.wikipedia.org/wiki/Thread_(computing)>`_, so you need a
thread-aware debugger to do more than load code, start, and stop it. A thread-aware debugger will allow you to switch
threads to the one that is running the code you're interested in, for instance your application, or an operating system
network thread. So far, OpenOCD is the only supported NuttX thread-aware debugger.

You will need an OpenOCD-compatible hardware adapter, ideally a fast one (USB 2.0 High Speed). This guide assumes you
are using the `Olimex ARM USB TINY H <https://www.olimex.com/Products/ARM/JTAG/ARM-USB-TINY-H/>`_.
(`Olimex ARM USB TINY H on Amazon <https://smile.amazon.com/Olimex-ARM-USB-TINY-H-Arm-Jtag/dp/B009UED630/>`_.) Other
adapters may work, follow the OpenOCD instructions and the instructions that came with your adapter.

You'll need to use the `Sony fork of OpenOCD <https://github.com/sony/openocd-nuttx>`_. Download and install it
according to the OpenOCD instructions.

See this article for more info:
`Debugging a Apache NuttX target with GDB and OpenOCD <https://micro-ros.github.io/docs/tutorials/advanced/debugging_gdb_openocd/>`_.

See the section :ref:`Running <running>` for a brief tutorial on how to use GDB.

----

Next up is :ref:`organization`.