README
^^^^^^

  o Installation
    - Installing Cygwin
    - Download and Unpack
    - Semi-Optional apps/ Package
    - Installation Directories with Spaces in the Path
    - Downloading from Repositories
    - Notes about Header Files
  o Configuring NuttX
    - Instantiating "Canned" Configurations
    - Refreshing Configurations
    - NuttX Configuration Tool
    - Finding Selections in the Configuration Menus
    - 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
^^^^^^^^^^^^

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

  NuttX may be installed and built on a Linux system or on a Windows
  system if Cygwin is installed.  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, internet installation
  for you.

     NOTE: 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).

  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.

  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!

  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 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 editing 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.  Cloning
    instructions are available here:

      https://sourceforge.net/p/nuttx/git

  Configuring the Cone

    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

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.

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 at ../misc/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 ../misc/tools/kconfig-language.txt.

  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 ../misc/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 at ../misc/tools/README.txt

     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), 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

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.

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 SourceForge 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! To work around this annoying behavior, do 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.

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:
  http://code.google.com/p/conemu-maximus5/

  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/.

  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
  installation.  My recommendation is that you download the GNUWin32 tools
  directly from the sourceforge.net website so that you will know what you are
  using and can reproduce your build environment.

  GNUWin32 Installation Steps:

  The following steps will download and execute the GNUWin32 installer.

  1. Download GetGNUWin32-x.x.x.exe from
     http://sourceforge.net/projects/getgnuwin32/files/.  This is the
     installer.  The current version as of this writing is 0.6.3.

  2. Run the installer.

  3. Accept the license.

  4. Select the installation directory.  My recommendation is the
     directory that contains this README file (<this-directory>).

  5. After running GetGNUWin32-0.x.x.exe, you will have a new directory
     <this-directory>/GetGNUWin32

  Note that the GNUWin32 installer didn't install GNUWin32.  Instead, it
  installed another, smarter downloader.  That downloader is the GNUWin32
  package management tool developed by the Open SSL project.

  The following steps probably should be performed from inside a DOS shell.

  6. Change to the directory created by GetGNUWin32-x.x.x.exe

    cd GetGNUWin32

  7. Execute the download.bat script.  The download.bat script will download
     about 446 packages!  Enough to have a very complete Linux-like environment
     under the DOS shell.  This will take awhile.  This step only downloads
     the packages and the next step will install the packages.

     download

  8. This step will install the downloaded packages.  The argument of the
     install.bat script is the installation location.  C:\gnuwin32 is the
     standard install location:

     install C:\gnuwin32

  NOTE:  This installation step will install *all* GNUWin32 packages... far
  more than you will ever need.  If disc space is a problem for you, you might
  need to perform a manual installation of the individual ZIP files that you
  will find in the <this directory>/GetGNUWin32/packages directory.

CYGWIN BUILD PROBLEMS
^^^^^^^^^^^^^^^^^^^^^

Strange Path Problems
---------------------

  If you see strange behavior when building under Cygwin then you may have
  a problem with your PATH variable.  For example, if you see failures to
  locate files that are clearly present, that may mean that you are using
  the wrong version of a tool.  For example, you may not be using Cygwin's
  'make' program at /usr/bin/make.  Try:

    $ which make
    /usr/bin/make

  When you install some toolchains (such as Yargarto or CodeSourcery tools),
  they may modify your PATH variable to include a path to their binaries.
  At that location, they make have GNUWin32 versions of the tools.  So you
  might actually be using a version of make that does not understand Cygwin
  paths.

  The solution is either:

  1. Edit your PATH to remove the path to the GNUWin32 tools, or
  2. Put /usr/local/bin, /usr/bin, and /bin at the front of your path:

     $ export PATH=/usr/local/bin:/usr/bin:/bin:$PATH

Window Native Toolchain Issues
------------------------------

  There are many popular Windows native toolchains that may be used with NuttX.
  Examples include CodeSourcery (for Windows), devkitARM, and several vendor-
  provied toolchains.  There are several limitations with using a and Windows
  based toolchain in a Cygwin environment.  The three biggest are:

  1. The Windows toolchain cannot follow Cygwin paths.  Path conversions are
     performed automatically in the Cygwin makefiles using the 'cygpath' utility
     but you might easily find some new path problems.  If so, check out 'cygpath -w'

  2. Windows toolchains cannot follow Cygwin symbolic links.  Many symbolic links
     are used in Nuttx (e.g., include/arch).  The make system works around these
     problems for the Windows tools by copying directories instead of linking them.
     But this can also cause some confusion for you:  For example, you may edit
     a file in a "linked" directory and find that your changes had no effect.
     That is because you are building the copy of the file in the "fake" symbolic
     directory.  If you use a Windows toolchain, you should get in the habit of
     making like this:

       make clean_context all

     An alias in your .bashrc file might make that less painful.  The rebuild
     is not a long as you might think because there is no dependency checking
     if you are using a native Windows toolchain.  That bring us to #3:

  3. Dependencies are not made when using Windows versions of the GCC on a POSIX
     platform (i.e., Cygwin).  This is because the dependencies are generated
     using Windows paths which do not work with the Cygwin make.

       MKDEP                = $(TOPDIR)/tools/mknulldeps.sh

     If you are building natively on Windows, then no such conflict exists
     and the best selection is:

       MKDEP                = $(TOPDIR)/tools/mkdeps.exe

General Pre-built Toolchain Issues

  To continue with the list of "Window Native Toolchain Issues" we can add
  the following.  These, however, are really just issues that you will have
  if you use any pre-built toolchain (vs. building the NuttX toolchain from
  the NuttX buildroot package):

  There may be incompatibilities with header files, libraries, and compiler
  built-in functions at detailed below.  For the most part, these issues
  are handled in the existing make logic.  But if you are breaking new ground,
  then you may encounter these:

  4. Header Files.  Most pre-built toolchains will build with a foreign C
     library (usually newlib, but maybe uClibc or glibc if you are using a
     Linux toolchain).  This means that the header files from the foreign
     C library will be built into the toolchain.  So if you "include <stdio.h>",
     you will get the stdio.h from the incompatible, foreign C library and
     not the nuttx stdio.h (at nuttx/include/stdio.h) that you wanted.

     This can cause really confusion in the builds and you must always be
     sure the -nostdinc is included in the CFLAGS.  That will assure that
     you take the include files only from

  5. Libraries.  What was said above header files applies to libraries.
     You do not want to include code from the libraries of any foreign
     C libraries built into your toolchain.  If this happens you will get
     perplexing errors about undefined symbols.  To avoid these errors,
     you will need to add -nostdlib to your CFLAGS flags to assure that
     you only take code from the NuttX libraries.

     This, however, may causes other issues for libraries in the toolchain
     that you do want (like libgcc.a or libm.a).  These are special-cased
     in most Makefiles, but you could still run into issues of missing
     libraries.

  6. Built-Ins.  Some compilers target a particular operating system.
     Many people would, for example, like to use the same toolchain to
     develop Linux and NuttX software.  Compilers built for other
     operating systems may generate incompatible built-in logic and,
     for this reason, -fno-builtin should also be included in your
     C flags

  And finally you may not be able to use NXFLAT.

  7. NXFLAT. If you use a pre-built toolchain, you will lose all support
     for NXFLAT.  NXFLAT is a binary format described in
     Documentation/NuttXNxFlat.html.  It may be possible to build
     standalone versions of the NXFLAT tools; there are a few examples
     of this in the misc/buildroot/configs directory.  However, it
     is possible that there could be interoperability issues with
     your toolchain since they will be using different versions of
     binutils and possibly different ABIs.

Building Original Linux Boards in Cygwin

  Some default board configurations are set to build under Linux and others
  to build under Windows with Cygwin.  Various default toolchains may also
  be used in each configuration.  It is possible to change the default
  setup.  Here, for example, is what you must do in order to compile a
  default Linux configuration in the Cygwin environment using the
  CodeSourceery for Windows toolchain.  After instantiating a "canned"
  NuttX configuration, run the target 'menuconfig' and set the following
  items:

    Build Setup->Build Host Platform->Windows
    Build Setup->Windows Build Environment->Cygwin
    System Type->Toolchain Selection->CodeSourcery GNU Toolchain under Windows

  In Windows 7 it may be required to open the Cygwin shell as Administrator
  ("Run As" option, right button) you find errors like "Permission denied".

Recovering from Bad Configurations

  Many people make the mistake of configuring NuttX with the "canned"
  configuration and then just typing 'make' with disastrous consequences;
  the build may fail with mysterious, uninterpretable, and irrecoverable
  build errors.  If, for example, you do this with an unmodified Linux
  configuration in a Windows/Cgwin environment, you will corrupt the
  build environment.  The environment will be corrupted because of POSIX vs
  Windows path issues and with issues related to symbolic links.  If you
  make the mistake of doing this, the easiest way to recover is to just
  start over: Do 'make distclean' to remove every trace of the corrupted
  configuration, reconfigure from scratch, and make certain that the set
  the configuration correctly for your platform before attempting to make
  again.

  Just fixing the configuration file after you have instantiated the bad
  configuration with 'make' is not enough.

DOCUMENTATION
^^^^^^^^^^^^^

Additional information can be found in the Documentation/ directory and
also in README files that are scattered throughout the source tree.  The
documentation is in HTML and can be access by loading the following file
into your Web browser:

  Documentation/index.html

NuttX documentation is also available online at http://www.nuttx.org.

Below is a guide to the available README files in the NuttX source tree:

nuttx
 |
 |- arch/
 |   |
 |   |- arm/
 |   |   `- src
 |   |       `- lpc214x/README.txt
 |   |- sh/
 |   |   |- include/
 |   |   |   `-README.txt
 |   |   |- src/
 |   |   |   `-README.txt
 |   |- x86/
 |   |   |- include/
 |   |   |   `-README.txt
 |   |   `- src/
 |   |       `-README.txt
 |   `- z80/
 |   |   `- src/
 |   |       |- z80/README.txt
 |   |       `- z180/README.txt, z180_mmu.txt
 |   `- README.txt
 |- audio/
 |   `-README.txt
 |- binfmt/
 |   `-libpcode/
 |       `-README.txt
 |- configs/
 |   |- amber/
 |   |   `- README.txt
 |   |- arduino-due/
 |   |   `- README.txt
 |   |- avr32dev1/
 |   |   `- README.txt
 |   |- c5471evm/
 |   |   `- README.txt
 |   |- cc3200-launchpad/
 |   |   `- README.txt
 |   |- cloudctrl
 |   |   `- README.txt
 |   |- compal_e86
 |   |   `- README.txt
 |   |- compal_e88
 |   |   `- README.txt
 |   |- compal_e99
 |   |   `- README.txt
 |   |- demo0s12ne64/
 |   |   `- README.txt
 |   |- dk-tm4c129x/
 |   |   `- README.txt
 |   |- ea3131/
 |   |   `- README.txt
 |   |- ea3152/
 |   |   `- README.txt
 |   |- eagle100/
 |   |   `- README.txt
 |   |- efm32-g8xx-stk/
 |   |   `- README.txt
 |   |- efm32gg-stk3700/
 |   |   `- README.txt
 |   |- ekk-lm3s9b96/
 |   |   `- README.txt
 |   |- ez80f910200kitg/
 |   |   |- ostest/README.txt
 |   |   `- README.txt
 |   |- ez80f910200zco/
 |   |   |- dhcpd/README.txt
 |   |   |- httpd/README.txt
 |   |   |- nettest/README.txt
 |   |   |- nsh/README.txt
 |   |   |- ostest/README.txt
 |   |   |- poll/README.txt
 |   |   `- README.txt
 |   |-  fire-stm32v2/
 |   |   `- README.txt
 |   |-  freedom-kl25z/
 |   |   `- README.txt
 |   |- galileo/
 |   |   `- README.txt
 |   |- hymini-stm32v/
 |   |   `- README.txt
 |   |- kwikstik-k40/
 |   |   `- README.txt
 |   |- lincoln60/
 |   |   `- README.txt
 |   |- lm3s6432-s2e/
 |   |   `- README.txt
 |   |- lm3s6965-ek/
 |   |   `- README.txt
 |   |- lm3s8962-ek/
 |   |   `- README.txt
 |   |- lpc4330-xplorer/
 |   |   `- README.txt
 |   |- lpc4357-evb/
 |   |   `- README.txt
 |   |- lpcxpresso-lpc1768/
 |   |   `- README.txt
 |   |- maple/
 |   |   `- README.txt
 |   |- mbed/
 |   |   `- README.txt
 |   |- mcu123-lpc214x/
 |   |   `- README.txt
 |   |- micropendous3/
 |   |   `- README.txt
 |   |- mikroe-stm32f/
 |   |   `- README.txt
 |   |- mirtoo/
 |   |   `- README.txt
 |   |- mt-db-x3/
 |   |   `- README.txt
 |   |- mx1ads/
 |   |   `- README.txt
 |   |- ne63badge/
 |   |   `- README.txt
 |   |- ntosd-dm320/
 |   |   |- doc/README.txt
 |   |   `- README.txt
 |   |- nucleo-f4x1re/
 |   |   `- README.txt
 |   |- nucleus2g/
 |   |   `- README.txt
 |   |- nutiny-nuc120/
 |   |   `- README.txt
 |   |- olimex-efm32g880f129-stk/
 |   |   `- README.txt
 |   |- olimex-lpc1766stk/
 |   |   `- README.txt
 |   |- olimex-lpc2378/
 |   |   `- README.txt
 |   |- olimex-lpc-h3131/
 |   |   `- README.txt
 |   |- olimex-stm32-h405/
 |   |   `- README.txt
 |   |- olimex-stm32-p107/
 |   |   `- README.txt
 |   |- olimex-stm32-p207/
 |   |   `- README.txt
 |   |- olimex-strp711/
 |   |   `- README.txt
 |   |- open1788/
 |   |   `- README.txt
 |   |- p112/
 |   |   `- README.txt
 |   |- pcblogic-pic32mx/
 |   |   `- README.txt
 |   |- pcduino-a10/
 |   |   `- README.txt
 |   |- pic32-starterkit/
 |   |   `- README.txt
 |   |- pic32mx7mmb/
 |   |   `- README.txt
 |   |- pirelli_dpl10/
 |   |   `- README.txt
 |   |- qemu-i486/
 |   |   `- README.txt
 |   |- rgmp/
 |   |   `- README.txt
 |   |- sama5d3x-ek/
 |   |   `- README.txt
 |   |- sama5d3-xplained/
 |   |   `- README.txt
 |   |- sama5d4-ek/
 |   |   `- README.txt
 |   |- samd20-xplained/
 |   |   `- README.txt
 |   |- sam3u-ek/
 |   |   `- README.txt
 |   |- sam4e-ek/
 |   |   `- README.txt
 |   |- sam4l-xplained/
 |   |   `- README.txt
 |   |- sam4s-xplained/
 |   |   `- README.txt
 |   |- sam4s-xplained-pro/
 |   |   `- README.txt
 |   |- sim/
 |   |   `- README.txt
 |   |- shenzhou/
 |   |   `- README.txt
 |   |- skp16c26/
 |   |   `- README.txt
 |   |- spark/
 |   |   `- README.txt
 |   |- stm3210e-eval/
 |   |   |- RIDE/README.txt
 |   |   `- README.txt
 |   |- stm3220g-eval/
 |   |   `- README.txt
 |   |- stm3240g-eval/
 |   |   `- README.txt
 |   |- stm32_tiny/
 |   |   `- README.txt
 |   |- stm32f3discovery/
 |   |   `- README.txt
 |   |- stm32f4discovery/
 |   |   `- README.txt
 |   |- stm32f429i-disco/
 |   |   |- ltdc/README.txt
 |   |   `- README.txt
 |   |- stm32ldiscovery/
 |   |   `- README.txt
 |   |- stm32vldiscovery/
 |   |   `- README.txt
 |   |- sure-pic32mx/
 |   |   `- README.txt
 |   |- teensy/
 |   |   `- README.txt
 |   |- tm4c123g-launchpad/
 |   |   `- README.txt
 |   |- twr-k60n512/
 |   |   `- README.txt
 |   |- ubw32/
 |   |   `- README.txt
 |   |- us7032evb1/
 |   |   `- README.txt
 |   |- viewtool-stm32f107/
 |   |   `- README.txt
 |   |- vsn/
 |   |   |- src/README.txt
 |   |   `- README.txt
 |   |- xtrs/
 |   |   `- README.txt
 |   |- z16f2800100zcog/
 |   |   |- ostest/README.txt
 |   |   |- pashello/README.txt
 |   |   `- README.txt
 |   |- z80sim/
 |   |   `- README.txt
 |   |- z8encore000zco/
 |   |   |- ostest/README.txt
 |   |   `- README.txt
 |   |- z8f64200100kit/
 |   |   |- ostest/README.txt
 |   |   `- README.txt
 |   |- zkit-arm-1769/
 |   |   `- README.txt
 |   |- zp214xpa/
 |   |   `- README.txt
 |   `- README.txt
 |- drivers/
 |   |- eeprom/
 |   |   `- README.txt
 |   |- lcd/
 |   |   `- README.txt
 |   |- mtd/
 |   |   `- README.txt
 |   |- sensors/
 |   |   `- README.txt
 |   |- sercomm/
 |   |   `- README.txt
 |   |- syslog/
 |   |   `- README.txt
 |   `- README.txt
 |- fs/
 |   |- binfs/
 |   |   `- README.txt
 |   |- mmap/
 |   |   `- README.txt
 |   |- nxffs/
 |   |   `- README.txt
 |   |- smartfs/
 |   |   `- README.txt
 |   `- procfs/
 |       `- README.txt
 |- graphics/
 |   `- README.txt
 |- lib/
 |   `- README.txt
 |- libc/
 |   `- README.txt
 |- libnx/
 |   `- README.txt
 |- libxx/
 |   `- README.txt
 |- mm/
 |   |- shm/
 |   |   `- README.txt
 |   `- README.txt
 |- net/
 |   `- README.txt
 |- syscall/
 |   `- README.txt
 `- tools/
     `- README.txt

apps
 |- examples/
 |   |- bastest/README.txt
 |   |- json/README.txt
 |   |- pashello/README.txt
 |   `- README.txt
 |- graphics/
 |   `- tiff/README.txt
 |- interpreters/
 |   |- bas
 |   |  `- README.txt
 |   |- ficl
 |   |  `- README.txt
 |   `- README.txt
 |- modbus/
 |   `- README.txt
 |- netutils/
 |   |- discover
 |   |  `- README.txt
 |   |- ftpc
 |   |  `- README.txt
 |   |- json
 |   |  `- README.txt
 |   |- telnetd
 |   |  `- README.txt
 |   `- README.txt
 |- nshlib/
 |   `- README.txt
 |- NxWidgets/
 |   `- README.txt
 |- system/
 |   |- cdcacm
 |   |  `- README.txt
 |   |- i2c
 |   |  `- README.txt
 |   |- inifile
 |   |  `- README.txt
 |   |- install
 |   |  `- README.txt
 |   |- nxplayer
 |   |  `- README.txt
 |   |- usbmsc
 |   |  `- README.txt
 |   `- zmodem
 |      `- README.txt
 `- README.txt

 NxWidgets
 |- Doxygen
 |   `- README.txt
 |- tools
 |   `- README.txt
 |- UnitTests
 |   `- README.txt
 `- README.txt