README.txt

README
^^^^^^

  o Installation
    - Installing Cygwin
    - Download and Unpack
    - Semi-Optional apps/ Package
    - Installation Directories with Spaces in the Path
    - Downloading from Repositories
    - Related Repositories
    - Notes about Header Files
  o Configuring NuttX
    - Instantiating "Canned" Configurations
    - Refreshing Configurations
    - NuttX Configuration Tool
    - Finding Selections in the Configuration Menus
    - Reveal Hidden Configuration Options
    - Comparing Two Configurations
    - Incompatibilities with Older Configurations
    - NuttX Configuration Tool under DOS
  o Toolchains
    - Cross-Development Toolchains
    - NuttX Buildroot Toolchain
  o Shells
  o Building NuttX
    - Building
    - Re-building
    - Build Targets and Options
    - Native Windows Build
    - Installing GNUWin32
  o Cygwin Build Problems
    - Strange Path Problems
    - Window Native Toolchain Issues
  o Documentation

INSTALLATION
^^^^^^^^^^^^

  NuttX may be installed and built on a Linux system or on a Windows
  system if Cygwin is installed.  The MSYS environment is an option
  to Cygwin on the Windows platform.  However, I have little experience
  that that configuration and it will not be discussed in this README
  file.

  Instructions for installation of Cygwin on Windows system are provided
  in the following paragraph.

  NuttX can also be installed and built on a native Windows system, but
  with some potential tool-related issues (see the discussion "Native
  Windows Build" below).

Installing Cygwin
-----------------

  Installing Cygwin on your Windows PC is simple, but time consuming.  See
  http://www.cygwin.com/ for installation instructions. Basically you just
  need to download a tiny setup.exe program and it does the real, network
  installation for you.

  Some Cygwin installation tips:

  1. Install at C:\cygwin

  2. Install EVERYTHING:  "Only the minimal base packages from the
     Cygwin distribution are installed by default. Clicking on categories
     and packages in the setup.exe package installation screen will
     provide you with the ability to control what is installed or updated.
     Clicking on the "Default" field next to the "All" category will
     provide you with the opportunity to install every Cygwin package.
     Be advised that this will download and install hundreds of megabytes
     to your computer."

     If you use the "default" installation, you will be missing many
     of the Cygwin utilities that you will need to build NuttX.  The
     build will fail in numerous places because of missing packages.

     NOTE: You don't really have to install EVERYTHING but I cannot
     answer the question "Then what should I install?"  I don't know
     the answer to that and so will continue to recommend installing
     EVERYTHING.

     You should certainly be able to omit "Science", "Math", and
     "Publishing".  You can try omitting KDE, Gnome, GTK, and other
     graphics packages if you don't plan to use them.

  After installing Cygwin, you will get lots of links for installed
  tools and shells.  I use the RXVT native shell.  It is fast and reliable
  and does not require you to run the Cygwin X server (which is neither
  fast nor reliable).  Unless otherwise noted, the rest of these
  instructions assume that you are at a bash command line prompt in
  either Linux or in Cygwin shell.

  UPDATE: The last time I installed EVERTHING, the download was
  about 5GiB.  The server I selected was also very slow so it took
  over a day to do the whole install!

Download and Unpack
-------------------

  Download and unpack the NuttX tarball.  If you are reading this, then
  you have probably already done that.  After unpacking, you will end
  up with a directory called nuttx-version (where version is the NuttX
  version number). You might want to rename that directory nuttx to
  match the various instructions in the documentation and some scripts
  in the source tree.

Semi-Optional apps/ Package
---------------------------

  All NuttX libraries and example code used to be in included within
  the NuttX source tree.  As of NuttX-6.0, this application code was
  moved into a separate tarball, the apps tarball.  If you are just
  beginning with NuttX, then you will want to download the versioned
  apps tarball along with the NuttX tarball.  If you already have your
  own product application directory, then you may not need the apps
  tarball.

  It is call "Semi-optional" because if you don't have some apps/
  directory, NuttX will *fail* to build! You do not necessarily need
  to use the NuttX apps tarball but may, instead, provide your own
  custom application directory.  Such a custom directory would need
  to include a valid Makefile to support the build and a valid Kconfig
  file to support the configuration.  More about these file later.

  Download then unpack the apps tarball in the same directory where you
  unpacked the NuttX tarball.  After you unpack the apps tarball, you
  will have a new directory called apps-version (where the version
  should exactly match the version of the NuttX tarball).  Again, you
  might want to rename the directory to simply apps/ to match what
  you read in the documentation

  After unpacking (and renaming) the apps tarball, you will have two
  directories side by side like this:

             |
        +----+----+
        |         |
      nuttx/     apps/

  This is important because the NuttX build will expect to find the
  apps directory in that (default) location.  That default location
  can be changed by modifying your NuttX configuration file, but that
  is another story.

Installation Directories with Spaces in the Path
------------------------------------------------

  The nuttx build directory should reside in a path that contains no
  spaces in any higher level directory name.  For example, under
  Cygwin, your home directory might be formed from your first and last
  names like: "/home/First Last". That will cause strange errors when
  the make system tries to build.

  [Actually, that problem is probably not to difficult to fix.  Some
   Makefiles probably just need some paths within double quotes]

  I work around spaces in the home directory name, by creating a
  new directory that does not contain any spaces, such as /home/nuttx.
  Then I install NuttX in /home/nuttx and always build from
  /home/nuttx/nuttx-code.

Downloading from Repositories
-----------------------------

  Cloning the Repository

    The current NuttX du jour is available in from a GIT repository.  Here are
    instructions for cloning the core NuttX RTOS (corresponding to the nuttx
    tarball discussed above)::

      git clone https://bitbucket.org/nuttx/nuttx.git nuttx

    And the semi-optional apps/ application directory and be cloned like:

      git clone https://bitbucket.org/nuttx/apps.git apps

    That will give you the same directory structure like this:

             |
        +----+----+
        |         |
      nuttx/     apps/

  Configuring the Clones

    The following steps need to be performed for each of the repositories.
    After changing to the clone directory:

    Set your identity:

      git config --global user.name "My Name"
      git config --global user.email my.name@example.com

    Colorized diffs are much easier to read:

      git config --global color.branch auto
      git config --global color.diff auto
      git config --global color.interactive auto
      git config --global color.status auto

    Checkout other settings

      git config --list

  Cloning NuttX Inside Cygwin

    If you are cloning the NuttX repository, it is recommended to avoid
    automatic end of lines conversions by git. These conversions may break
    some scripts like configure.sh. Before cloning, do the following:

      git config --global core.autocrlf false

Related Repositories
--------------------

  These are standalone repositories:

  * https://bitbucket.org/nuttx/apps

    This directory holds an optional package of applications and libraries
    can be used with the NuttX RTOS.  There is a README.txt file there that
    will provide a more information about that package.

  * https://bitbucket.org/nuttx/nxwidgets

    This is the NuttX C++ graphics support.  This includes NxWM, the tiny
    NuttX Window Manager.

  * https://bitbucket.org/nuttx/uclibc

    This repository contains a version of the uClibc++ C++ library.  This code
    originates from http://cxx.uclibc.org/ and has been adapted for NuttX by the
    RGMP team (http://rgmp.sourceforge.net/wiki/index.php/Main_Page).

  * https://bitbucket.org/nuttx/buildroot

    A environment that you can to use to build a custom, NuttX GNU toolchain.

  * https://bitbucket.org/nuttx/tools

    There are snapshots of some tools here that you will need to work with
    NuttX:  kconfig-frontends, genromfs, and others.

  * https://bitbucket.org/nuttx/drivers

    A few drivers that are not integrated into the main NuttX source tree due
    to licensing issues.

  * https://bitbucket.org/nuttx/pascal

    Yes, this really is a Pascal compiler.  The Pascal p-code run-time and
    pcode debugger can be built as a part of NuttX.

Notes about Header Files
------------------------

  Other C-Library Header Files.

    When a GCC toolchain is built, it must be built against a C library.
    The compiler together with the contents of the C library completes the
    C language definition and provides the complete C development
    environment.  NuttX provides its own, built-in C library.  So the
    complete, consistent C language definition for use with NuttX comes from
    the combination of the compiler and the header files provided by the
    NuttX C library.

    When a GCC toolchain is built, it incorporates the C library header
    files into the compiler internal directories and, in this way, the C
    library really becomes a part of the toolchain.  If you use the NuttX
    buildroot toolchain as described below under under "NuttX Buildroot
    Toolchain", your GCC toolchain will build against the NuttX C library
    and will incorporate the NuttX C library header files as part of the
    toolchain.

    If you use some other, third-party tool chain, this will not be the
    case, however.  Those toolchains were probably built against some
    other, incompatible C library distribution (such as newlib).  Those
    tools will have incorporated the incompatible C library header files
    as part of the toolchain.  These incompatible header files must *not*
    be used with NuttX because the will conflict with definitions in the
    NuttX built-in C-Library.  For such toolchains that include header
    files from a foreign C-Library, NuttX must be compiled without using
    the standard header files that are distributed with your toolchain.
    This prevents including conflicting, incompatible header files such
    as stdio.h.

    The math.h and stdarg.h are probably the two most trouble some header
    files to deal with.  These troublesome header files are discussed in
    more detail below.

  Header Files Provided by Your Toolchain.

    Certain header files, such as setjmp.h, stdarg.h, and math.h, may still
    be needed from your toolchain and your compiler may not, however, be able
    to find these if you compile NuttX without using standard header file.
    If that is the case, one solution is to copy those header file from
    your toolchain into the NuttX include directory.

  Duplicated Header Files.

    There are also a few header files that can be found in the nuttx/include
    directory which are duplicated by the header files from your toolchain.
    stdint.h and stdbool.h are examples.  If you prefer to use the stdint.h
    and stdbool.h header files from your toolchain, those could be copied
    into the nuttx/include/ directory. Using most other header files from
    your toolchain would probably cause errors.

  math.h

    Even though you should not use a foreign C-Library, you may still need
    to use other, external libraries with NuttX.  In particular, you may
    need to use the math library, libm.a.  NuttX supports a generic, built-in
    math library that can be enabled using CONFIG_LIBM=y.  However, you may
    still want to use a higher performance external math library that has
    been tuned for your CPU.  Sometimes such such tuned math libraries are
    bundled with your toolchain.

    The math libary header file, math.h, is a then special case.  If you do
    nothing, the standard math.h header file that is provided with your
    toolchain will be used.

    If you have a custom, architecture specific math.h header file, then
    that header file should be placed at arch/<cpu>/include/math.h.  There
    is a stub math.h header file located at include/nuttx/math.h.  This stub
    header file can be used to "redirect" the inclusion to an architecture-
    specific math.h header file.  If you add an architecture specific math.h
    header file then you should also define CONFIG_ARCH_MATH_H=y in your
    NuttX Configuration file.  If CONFIG_ARCH_MATH_H is selected, then the
    top-level Makefile will copy the stub math.h header file from
    include/nuttx/math.h to include/math.h where it will become the system
    math.h header file.  The stub math.h header file does nothing other
    than to include that architecture-specific math.h header file as the
    system math.h header file.

  float.h

    If you enable the generic, built-in math library, then that math library
    will expect your toolchain to provide the standard float.h header file.
    The float.h header file defines the properties of your floating point
    implementation.  It would always be best to use your toolchain's float.h
    header file but if none is available, a default float.h header file will
    provided if this option is selected.  However, there is no assurance that
    the settings in this float.h are actually correct for your platform!

  stdarg.h

    In most cases, the correct version of stdarg.h is the version provided
    with your toolchain.  However, sometimes there are issues with with
    using your toolchains stdarg.h.  For example, it may attempt to draw in
    header files that do not exist in NuttX or perhaps the header files that
    is uses are not compatible with the NuttX header files.  In those cases,
    you can use an architecture-specific stdarg.h header file by defining
    CONFIG_ARCH_STDARG_H=y.

    See the discussion above for the math.h header.  This setting works
    exactly the same for the stdarg.h header file.

CONFIGURING NUTTX
^^^^^^^^^^^^^^^^^

Instantiating "Canned" Configurations
-------------------------------------

  "Canned" NuttX configuration files are retained in:

    configs/<board-name>/<config-dir>

  Where <board-name> is the name of your development board and <config-dir>
  is the name of the sub-directory containing a specific configuration for
  that board.  Configuring NuttX requires only copying three files from the
  <config-dir> to the directory where you installed NuttX (TOPDIR) (and
  sometimes one additional file to the directory the NuttX application
  package (APPSDIR)):

    Copy configs/<board-name>/<config-dir>/Make.def to ${TOPDIR}/Make.defs

      Make.defs describes the rules needed by you tool chain to compile
      and link code.  You may need to modify this file to match the
      specific needs of your toolchain.

    Copy configs/<board-name>/<config-dir>/setenv.sh to ${TOPDIR}/setenv.sh

      setenv.sh is an optional convenience file that I use to set
      the PATH variable to the toolchain binaries.  You may chose to
      use setenv.sh or not.  If you use it, then it may need to be
      modified to include the path to your toolchain binaries.

    Copy configs/<board-name>/<config-dir>/defconfig to ${TOPDIR}/.config

      The defconfig file holds the actual build configuration.  This
      file is included by all other make files to determine what is
      included in the build and what is not.  This file is also used
      to generate a C configuration header at include/nuttx/config.h.

   General information about configuring NuttX can be found in:

      ${TOPDIR}/configs/README.txt
      ${TOPDIR}/configs/<board-name>/README.txt

    There is a configuration script in the tools/ directory that makes this
    easier.  It is used as follows:

      cd ${TOPDIR}/tools
      ./configure.sh <board-name>/<config-dir>

    There is an alternative Windows batch file that can be used in the
    windows native environment like:

      cd ${TOPDIR}\tools
      configure.bat <board-name>\<config-dir>

    See tools/README.txt for more information about these scripts.

Refreshing Configurations
-------------------------

  Configurations can get out of date.  As new configuration settings are
  added or removed or as dependencies between configuration settings
  change, the contents of a default configuration can become out of synch
  with the build systems.  Hence, it is a good practice to "refresh" each
  configuration after configuring and before making.  To refresh the
  configuration, use the NuttX Configuration Tool like this:

    make oldconfig

  AFTER you have instantiated the NuttX configuration as described above.
  The configuration step copied the .config file into place in the top-level
  NuttX directory; 'make oldconfig' step will then operate on that .config
  file to bring it up-to-date.

  If you configuration is out of date, you will be prompted by 'make oldconfig'
  to resolve the issues detected by the configuration tool, that is, to
  provide values for the new configuration options in the build system.  Doing
  this can save you a lot of problems down the road due to obsolete settings in
  the default board configuration file.  The NuttX configuration tool is
  discussed in more detail in the following paragraph.

  Confused about what the correct value for a new configuration item should
  be?  Enter ? in response to the 'make oldconfig' prompt and it will show
  you the help text that goes with the option.

  If you don't want to make any decisions are are willing to just accept the
  recommended default value for each new configuration item, an even easier
  way is:

    make oldefconfig

  The olddefconfig target will simply bring you configuration up to date with
  the current Kconfig files, setting any new options to the default value.
  No questions asked.

NuttX Configuration Tool
------------------------

  An automated tool has been incorported to support re-configuration
  of NuttX.  This automated tool is based on the kconfig-frontends
  application available at http://ymorin.is-a-geek.org/projects/kconfig-frontends
  (A snapshot of this tool is also available fromo the tools repository at
  https://bitbucket.org/nuttx/tools).  This application provides a tool
  called 'kconfig-mconf' that is used by the NuttX top-level Makefile.
  The following make target is provided:

    make menuconfig

  This make target will bring up NuttX configuration menus.

  WARNING:  Never do 'make menuconfig' on a configuration that has
  not been converted to use the kconfig-frontends tools!  This will
  damage your configuration (see
  http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig).

  How do we tell a new configuration from an old one? See "Incompatibilities
  with Older Configurations" below.

  The 'menuconfig' make target depends on two things:

  1. The Kconfig configuration data files that appear in almost all
     NuttX directories.  These data files are the part that is still
     under development (patches are welcome!).  The Kconfig files
     contain configuration information for the configuration settings
     relevant to the directory in which the Kconfig file resides.

     NOTE: For a description of the syntax of this configuration file,
     see kconfig-language.txt in the tools repository at
     https://bitbucket.org/nuttx/tools

  2. The 'kconfig-mconf' tool.  'kconfig-mconf' is part of the
     kconfig-frontends package.  You can download that package from
     the website http://ymorin.is-a-geek.org/projects/kconfig-frontends
     or you can use the snapshot in the tools repository at
     https://bitbucket.org/nuttx/tools.

     Building kconfig-frontends under Linux may be as simple as
     'configure; make; make install' but there may be some build
     complexities, especially if you are building under Cygwin.  See
     the more detailed build instructions in the top-level README.txt
     file of the tools repository at https://bitbucket.org/nuttx/tools.

     The 'make install' step will, by default, install the 'kconfig-mconf'
     tool at /usr/local/bin/mconf.  Where ever you choose to
     install 'kconfig-mconf', make certain that your PATH variable includes
     a path to that installation directory.

     The kconfig-frontends tools will not build in a native Windows
     environment directly "out-of-the-box".  For the Windows native
     case, you should should the modified version of kconfig-frontends
     that can be found at
     http://uvc.de/posts/linux-kernel-configuration-tool-mconf-under-windows.html

  The basic configuration order is "bottom-up":

    - Select the build environment,
    - Select the processor,
    - Select the board,
    - Select the supported peripherals
    - Configure the device drivers,
    - Configure the application options on top of this.

  This is pretty straight forward for creating new configurations
  but may be less intuitive for modifying existing configurations.

  If you have an environment that supports the Qt or GTK graphical systems
  (probably KDE or gnome, respectively, or Cygwin under Windows with Qt or
  GTK installed), then you can also build the graphical kconfig-frontends,
  kconfig-qconf and kconfig-gconf.  In these case, you can start the
  graphical configurator with either:

    make qconfig

  or

    make gconfig

  Some keyboard shortcus supported by kconfig-mconf, the tool that runs
  when you do 'make menuconfig':

    - '?' will bring up the mconfig help display.

    - '/' can be used find configuration selections.

    - 'Z' can be used to reveal hidden configuration options

  These last to shortcuts are described further in the following
  paragraphs.

Finding Selections in the Configuration Menus
---------------------------------------------

  The NuttX configuration options have gotten complex and it can be very
  difficult to find options in the menu trees if you are not sure where
  to look.  The "basic configuration order" describe above can help to
  narrow things down.

  But if you know exactly what configuration setting you want to select,
  say CONFIG_XYZ, but not where to find it, then the 'make memconfig'
  version of the tool offers some help:  By pressing the '/' key, the
  tool will bring up a menu that will allow you to search for a
  configuration item.  Just enter the string CONFIG_XYZ and press 'ENTER'.
  It will show you not only where to find the configuration item, but
  also all of the dependencies related to the configuration item.

Reveal Hidden Configuration Options
-----------------------------------

  If you type 'Z', then kconfig-mconf will change what is displayed.
  Normally, only enabled features that have all of their dependencies met
  are displayed.  That is, of course, not very useful if you would like to
  discover new options or if you are looking for an option and do not
  realize that the dependencies have not yet been selected and, hence, it
  is not displayed.

  But if you enter 'Z', then every option will be shown, whether or not its
  dependencies have been met.  You can the see everything that could be
  selected with the right dependency selections.  These additional options
  will be shown the '-' for the selection and for the value (since it
  cannot be selected and has no value).  About all you do is to select
  the <Help> option to see what the dependencies are.

Comparing Two Configurations
----------------------------

  If you try to compare to configurations using 'diff', you will probably
  not be happy with the result.  There are superfluous things added to
  the configuration files that makes comparisons with the human eye
  difficult.

  There is a tool at nuttx/tools/cmpconfig.c that can be build to simplify
  these comparisons.  The output from this difference tools will show only
  the meaningful differences between two configuration files.  This tools
  built as follows:

    cd nuttx/tools
    make -f Makefile.host

  This will crate a program called 'cmpconfig' or 'comconfig.exe' on Windows.

  Why would you want to compare two configuration files?  Here are a few
  of reasons why I do this:

  1. When I create a new configuration I usually base it on an older
     configuration and I want to know, "What are the options that I need to
     change to add the new feature to the older configurations?"  For example,
     suppose that I have a boardA/nsh configuration and I want to create a
     boardA/nxwm configuration.  Suppose I already have boardB/nsh and
     boardB/nxwm configurations.  Then by comparing the boardB/nsh with the
     boardB/nxwm I can see the modifications that I would need to make to my
     boardA/nsh to create a new  boardA/nxwm.

  2. But the most common reason that I use the 'cmpconfig' program to to
     check the results of "refreshing" a configuration with 'make oldconfig'
     (see the paragraph "Refreshing Configurations" above).  The 'make
     oldconfig' command will make changes to my configuration and using
     'cmpconfig', I can see precisely what those changes were and if any
     should be of concern to me.

  3. The 'cmpconfig' tool can also be useful when converting older, legacy
     manual configurations to the current configurations based on the
     kconfig-frontends tools.  See the following paragraph.

Incompatibilities with Older Configurations
-------------------------------------------

  ***** WARNING *****

  The current NuttX build system supports *only* the new configuration
  files generated using the kconfig-frontends tools.  Support for the
  older, legacy, manual configurations was eliminated in NuttX 7.0; all
  configuration must now be done using the kconfig-frontends tool.  The
  older manual configurations and the new kconfig-frontends configurations
  are not compatible.  Old legacy configurations can *not* be used
  with the kconfig-frontends tool and, hence, cannot be used with releases
  of NuttX 7.0 and beyond:

  If you run 'make menuconfig' with a legacy configuration the resulting
  configuration will probably not be functional.

  Q: How can I tell if a configuration is a new kconfig-frontends
     configuration or an older, manual configuration?

  A: Only old, manual configurations will have an appconfig file


  Q: How can I convert a older, manual configuration into a new,
     kconfig-frontends toolchain.

  A: Refer to http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig

  ***** WARNING *****

  As described above, whenever you use a configuration, you really should
  always refresh the configuration the following command *before* you make
  NuttX:

    make oldconfig

  This will make sure that the configuration is up-to-date in the event that
  it has lapsed behind the current NuttX development (see the paragraph
  "Refreshing Configurations" above).  But this only works with *new*
  configuration files created with the kconfig-frontends tools

  Never do 'make oldconfig' (OR 'make menuconfig') on a  configuration that
  has not been converted to use the kconfig-frontends tools!  This will
  damage your configuration (see
  http://www.nuttx.org/doku.php?id=wiki:howtos:convertconfig).

NuttX Configuration Tool under DOS
----------------------------------

  Recent versions of NuttX support building NuttX from a native Windows
  console window (see "Native Windows Build" below).  But kconfig-frontends
  is a Linux tool.  At one time this was a problem for Windows users, but
  now there is a specially modified version of the kconfig-frontends tools
  that can be used:
  http://uvc.de/posts/linux-kernel-configuration-tool-mconf-under-windows.html

  It is also possible to use the version of kconfig-frontends built
  under Cygwin outside of the Cygwin "sandbox" in a native Windows
  environment:

  1. You can run the configuration tool using Cygwin.  However, the
     Cygwin Makefile.win will complain so to do this will, you have
     to manually edit the .config file:

      a. Delete the line: CONFIG_WINDOWS_NATIVE=y
      b. Change the apps/ directory path, CONFIG_APPS_DIR to use Unix
         style delimiters.  For example, change "..\apps" to "../apps"

     And of course, after you use the configuration tool you need to
     restore CONFIG_WINDOWS_NATIVE=y and the correct CONFIG_APPS_DIR.

  2) You can, with some effort, run the Cygwin kconfig-mconf tool
     directly in the Windows console window.  In this case, you do not
     have to modify the .config file, but there are other complexities:

      a. You need to temporarily set the Cgywin directories in the PATH
         variable then run kconfig-mconf manually like:

          kconfig-mconf Kconfig

         There is a Windows batch file at tools/kconfig.bat that automates
         these steps:

         tools/kconfig menuconfig

       b. There is an issue with accessing DOS environment variables from
          the Cygwin kconfig-mconf running in the Windows console.  The
          following change to the top-level Kconfig file seems to work
          around these problems:

          config APPSDIR
              string
          -   option env="APPSDIR"
          +   default "../apps"

TOOLCHAINS
^^^^^^^^^^

Cross-Development Toolchains
----------------------------

  In order to build NuttX for your board, you will have to obtain a cross-
  compiler to generate code for your target CPU.  For each board,
  configuration, there is a README.txt file (at configs/<board-name>/README.txt).
  That README file contains suggestions and information about appropriate
  tools and development environments for use with your board.

  In any case, the script, setenv.sh that was deposited in the top-
  level directory when NuttX was configured should be edited to set
  the path to where you installed the toolchain.  The use of setenv.sh
  is optional but can save a lot of confusion in the future.

NuttX Buildroot Toolchain
-------------------------

  For many configurations, a DIY set of tools is available for NuttX.  These
  tools can be downloaded from the NuttX Bitbucket.org file repository.  After
  unpacking the buildroot tarball, you can find instructions for building
  the tools in the buildroot/configs/README.txt file.

  Check the README.txt file in the configuration director for your board
  to see if you can use the buildroot toolchain with your board (this
  README.txt file is located in configs/<board-name>/README.txt).

  This toolchain is available for both the Linux and Cygwin development
  environments.

  Advantages:  (1) NuttX header files are built into the tool chain,
  and (2) related support tools like NXFLAT tools, the ROMFS
  genromfs tools, and the kconfig-frontends tools can be built into your
  toolchain.

  Disadvantages:  This tool chain is not was well supported as some other
  toolchains.  GNU tools are not my priority and so the buildroot tools
  often get behind.  For example, until recently there was no EABI support
  in the NuttX buildroot toolchain for ARM.

  NOTE: For Cortex-M3/4, there are OABI and EABI versions of the buildroot
  toolchains.  If you are using the older OABI toolchain the prefix for
  the tools will be arm-nuttx-elf-; for the EABI toolchain the prefix will
  be arm-nuttx-eabi-.  If you are using the older OABI toolchain with
  an ARM Cortex-M3/4, you will need to set CONFIG_ARMV7M_OABI_TOOLCHAIN
  in the .config file in order to pick the right tool prefix.

  If the make system ever picks the wrong prefix for your toolchain, you
  can always specify the prefix on the command to override the default
  like:

    make CROSSDEV=arm-nuttx-elf

SHELLS
^^^^^^

  The NuttX build relies on some shell scripts.  Some are inline in the
  Makefiles and many are executable scripts in the tools/. directory.  The
  scripts were all developed using bash and many contain bash shell
  dependencies.

  Most of the scripts begin with #!/bin/bash to specifically select the
  bash shell.  Some still have #!/bin/sh but I haven't heard any complaints
  so these must not have bash dependencies.

  There are two shell issues that I have heard of:

  1. Linux where /bin/sh refers to an incompatible shell (like ksh or csh).

     In this case, bash is probably available and the #!/bin/bash at the
     beginning of the file should do the job.  If any scripts with #!/bin/sh
     fail, try changing that to #!/bin/bash and let me know about the change.

  2. FreeBSD with the Bourne Shell and no bash shell.

     The other, reverse case has also been reported on FreeBSD setups that
     have the Bourne shell, but not bash.  In this base, #!/bin/bash fails
     but #!/bin/sh works okay.  My recommendation in this case is to create
     a symbolic link at /bin/bash that refers to the Bourne shell.

     There may still be issues, however, with certain the bash-centric scripts
     that will require modifications.

BUILDING NUTTX
^^^^^^^^^^^^^^

Building
--------

  NuttX builds in-place in the source tree.  You do not need to create
  any special build directories.  Assuming that your Make.defs is setup
  properly for your tool chain and that setenv.sh contains the path to where
  your cross-development tools are installed, the following steps are all that
  are required to build NuttX:

    cd ${TOPDIR}
    . ./setenv.sh
    make

  At least one configuration (eagle100) requires additional command line
  arguments on the make command.  Read ${TOPDIR}/configs/<board-name>/README.txt
  to see if that applies to your target.

Re-building
-----------

  Re-building is normally simple -- just type make again.

  But there are some things that can "get you" when you use the Cygwin
  development environment with Windows native tools.  The native Windows
  tools do not understand Cygwin's symbolic links, so the NuttX make system
  does something weird:  It copies the configuration directories instead of
  linking to them (it could, perhaps, use the NTFS 'mklink' command, but it
  doesn't).

  A consequence of this is that you can easily get confused when you edit
  a file in one of the linked (i.e., copied) directories, re-build NuttX,
  and then not see your changes when you run the program.  That is because
  build is still using the version of the file in the copied directory, not
  your modified file!

  Older versions of NuttX did not support dependiencies in this
  configuration.  So a simple work around this annoying behavior in this
  case was the following when you re-build:

     make clean_context all

  This 'make' command will remove of the copied directories, re-copy them,
  then make NuttX.

  However, more recent versions of NuttX do support dependencies for the
  Cygwin build.  As a result, the above command will cause everything to be
  rebuilt (beause it removes and will cause recreating the
  include/nuttx/config.h header file).  A much less gracefully but still
  effective command in this case is the following for the ARM configuration:

    rm -rf arch/arm/src/chip arch/arm/src/board

  This "kludge" simple removes the copied directories.  These directories
  will be re-created when you do a normal 'make' and your edits will then be
  effective.

Build Targets and Options
-------------------------

  Build Targets:
  Below is a summary of the build targets available in the top-level
  NuttX Makefile:

  all

    The default target builds the NuttX executable in the selected output
    formats.

  clean

    Removes derived object files, archives, executables, and temporary
    files, but retains the configuration and context files and directories.

  distclean

    Does 'clean' then also removes all configuration and context files.
    This essentially restores the directory structure to its original,
    unconfigured stated.

  Application housekeeping targets.  The APPDIR variable refers to the user
  application directory.  A sample apps/ directory is included with NuttX,
  however, this is not treated as part of NuttX and may be replaced with a
  different application directory.  For the most part, the application
  directory is treated like any other build directory in the Makefile script.
  However, as a convenience, the following targets are included to support
  housekeeping functions in the user application directory from the NuttX
  build directory.

  apps_clean

    Perform the clean operation only in the user application directory

  apps_distclean

    Perform the distclean operation only in the user application directory.
    The apps/.config file is preserved so that this is not a "full" distclean
    but more of a configuration "reset."

  export

    The export target will package the NuttX libraries and header files into
    an exportable package.  Caveats: (1) These needs some extension for the KERNEL
    build. (2) The logic in tools/mkexport.sh only supports GCC and, for example,
    explicitly assumes that the archiver is 'ar'

  download

    This is a helper target that will rebuild NuttX and download it to the target
    system in one step.  The operation of this target depends completely upon
    implementation of the DOWNLOAD command in the user Make.defs file.  It will
    generate an error an error if the DOWNLOAD command is not defined.

  The following targets are used internally by the make logic but can be invoked
  from the command under certain conditions if necessary.

  depend

    Create build dependencies. (NOTE:  There is currently no support for build
    dependencies under Cygwin using Windows-native toolchains.)

  context

    The context target is invoked on each target build to assure that NuttX is
    properly configured.  The basic configuration steps include creation of the
    the config.h and version.h header files in the include/nuttx directory and
    the establishment of symbolic links to configured directories.

  clean_context

    This is part of the distclean target.  It removes all of the header files
    and symbolic links created by the context target.

  Build Options:
  Of course, the value any make variable an be overridden from the make command
  line.  However, there is one particular variable assignment option that may
  be useful to you:

  V=1

    This is the build "verbosity flag."  If you specify V=1 on the make command
    line, you will see the exact commands used in the build. This can be very
    useful when adding new boards or tracking down compile time errors and
    warnings (Contributed by Richard Cochran).

Native Windows Build
--------------------

  The beginnings of a Windows native build are in place but still not often
  used as of this writing.  The windows native build logic initiated
  if CONFIG_WINDOWS_NATIVE=y is defined in the NuttX configuration file:

  This build:

    - Uses all Windows style paths
    - Uses primarily Windows batch commands from cmd.exe, with
    - A few extensions from GNUWin32

  In this build, you cannot use a Cygwin or MSYS shell. Rather the build must
  be performed in a Windows console window. Here is a better terminal than the
  standard issue, CMD.exe terminal:  ConEmu which can be downloaded from:
  https://sourceforge.net/projects/conemu/ or https://conemu.github.io/ .

  Build Tools.  The build still relies on some Unix-like commands.  I use
  the GNUWin32 tools that can be downloaded from http://gnuwin32.sourceforge.net/
  using the 'Download all' selection.  Individual packages can be download
  instead if you know what you are doing and want a faster download (No, I
  can't tell you which packages you should or should not download).

  Host Compiler:  I use the MingGW GCC compiler which can be downloaded from
  http://www.mingw.org/.  If you are using GNUWin32, then it is recommended
  the you not install the optional MSYS components as there may be conflicts.

  This capability should still be considered a work in progress because:

    (1) It has not been verified on all targets and tools, and
    (2) it still lacks some of the creature-comforts of the more mature
        environments.

  There is an alternative to the setenv.sh script available for the Windows
  native environment: tools/configure.bat.  See tools/README.txt for additional
  information.

Installing GNUWin32
-------------------

  The Windows native build will depend upon a few Unix-like tools that can be
  provided either by MSYS or GNUWin32.  The GNUWin32 are available from
  http://gnuwin32.sourceforge.net/.  GNUWin32 provides ports of tools with a
  GPL or similar open source license to modern MS-Windows (Microsoft Windows
  2000 / XP / 2003 / Vista / 2008 / 7).  See
  http://gnuwin32.sourceforge.net/packages.html for a list of all of the tools
  available in the GNUWin32 package.

  The SourceForge project is located here:
  http://sourceforge.net/projects/gnuwin32/.  The project is still being
  actively supported (although some of the Windows ports have gotten very old).

  Some commercial toolchains include a subset of the GNUWin32 tools in the