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<html>

<head>
<title>NuttX Porting Manual</title>
<meta name="author" content="Gregory Nutt">
</head>

<body background="backgd.gif">
<hr>
<center><h1><i>Under Construction</i></h1></center>
<hr>
<center>
  <big><b>
    <p>NuttX Operating System</p>
    <p>Porting Guide</p>
  </b></big>
  <p><small>by</small></p>
  <p>Gregory Nutt</p>
  <p><small>Last Update: March 26, 2007</small></p>
</center>

<center><h1>Table of Contents</h1></center>
<li>1.0 <a href="#Introduction">1.0 Introduction</a></li>
<li>2.0 <a href="#DirectoryStructure">Directory Structure</a></li>
<ul>
  <li>2.1 <a href="#DirStructDocumentation">Documentation</a></li>
  <l1>2.2 <a href="#DirStructArch">arch</a></li>
  <ul>
    <li><a href="#archdirectorystructure">2.2.1 Subdirectory Structure</a></li>
    <li><a href="#summaryofarchfiles">2.2.2 Summary of Files</a></li>
    <li><a href="#supportedarchitectures">2.2.3 Supported Architectures</a></li>
  </ul>
  <li>2.3 <a href="#DirStructConfigs">configs/</a></li>
  <ul>
    <li><a href="#configsdirectorystructure">2.3.1 Subdirectory Structure</a></li>
    <li><a href="#summaryofconfigfiles">2.3.2 Summary of Files</a></li>
    <ul>
      <li><a href="#boardlogic">2.3.2.1 Board Specific Logic</a></li>
      <li><a href="#boardconfigfiles">2.3.2.2 Board Specific Configuration Files</a></li>
    </ul>
    <li><a href="#supportedboards">2.3.3 Supported Boards</a></li>
  </ul>
  <li>2.4 <a href="#DirStructDrivers">drivers</a></li>
  <li>2.5 <a href="#DirStructExamples">examples</a></li>
  <li>2.6 <a href="#DirStructFs">fs</a></li>
  <li>2.7 <a href="#DirStructInclude">include</a></li>
  <li>2.8 <a href="#DirStructLib">lib</a></li>
  <li>2.9 <a href="#DirStructMm">mm</a></li>
  <li>2.10 <a href="#DirStructSched">sched</a></li>
  <li>2.11 <a href="#DirStructTools">tools</a></li>
  <li>2.12 <a href="#topmakefile">Makefile</a></li>
</ul>
<li>3.0 <a href="#configandbuild">Configuring and Building</a></li>
<ul>
  <li><a href="#configuringnuttx">3.1 Configuring NuttX</a></li>
  <li><a href="#buildingnuttx">3.2 Building NuttX</a></li>
</ul>
<li>4.0 <a href="#ArchAPIs">Architecture APIs</a></li>
<ul>
  <li><a href="#imports">4.1 APIs Exported by Architecture-Specific Logic to NuttX</a></li>
  <ul>
    <li><a href="#upinitialize">4.1.1 <code>up_initialize()</code></a></li>
    <li><a href="#upidle">4.1.2 <code>up_idle()</code></a></li>
    <li><a href="#upinitialstate">4.1.3 <code>up_initial_state()</code></a></li>
    <li><a href="#upcreatestack">4.1.4 <code>up_create_stack()</code></a></li>
    <li><a href="#upusestack">4.1.5 <code>up_use_stack()</code></a></li>
    <li><a href="#upreleasestack">4.1.6 <code>up_release_stack()</code></a></li>
    <li><a href="#upunblocktask">4.1.7 <code>up_unblock_task()</code></a></li>
    <li><a href="#upblocktask">4.1.8 <code>up_block_task()</code></a></li>
    <li><a href="#upreleasepending">4.1.9 <code>up_release_pending()</code></a></li>
    <li><a href="#upreprioritizertr">4.1.10 <code>up_reprioritize_rtr()</code></a></li>
    <li><a href="#_exit">4.1.11 <code>_exit()</code></a></li>
    <li><a href="#upassert">4.1.12 <code>up_assert()</code></a></li>
    <li><a href="#upschedulesigaction">4.1.13 <code>up_schedule_sigaction()</code></a></li>
    <li><a href="#upallocateheap">4.1.14 <code>up_allocate_heap()</code></a></li>
    <li><a href="#upinterruptcontext">4.1.15 <code>up_interrupt_context()</code></a></li>
    <li><a href="#updisableirq">4.1.16 <code>up_disable_irq()</code></a></li>
    <li><a href="#upenableirq">4.1.17 <code>up_enable_irq()</code></a></li>
    <li><a href="#upputc">4.1.18 <code>up_putc()</code></a></li>
  </ul>
  <li><a href="#exports">4.2 APIs Exported by NuttX to Architecture-Specific Logic</a></li>
  <ul>
    <li><a href="#osstart">4.2.1 <code>os_start()</code></a></li>
    <li><a href="#listmgmt">4.2.2 OS List Management APIs</a></li></li>
    <li><a href="#schedprocesstimer">4.2.3 <code>sched_process_timer()</code></a></li>
    <li><a href="#irqdispatch">4.2.4 <code>irq_dispatch()</code></a></li>
  </ul>
</ul>

<hr>
<h1>1.0 <a name="Introduction">Introduction</a></h1>

<p><b>Overview</b>
  This document provides and overview of the NuttX build and configuration
  logic and provides hints for the incorporation of new processor/board archectures
  into the build.
</p>
<p>
  See also <code>arch/README.txt</code> and <code>configs/README.txt</code>.
</p>

<p><b>General Philosophy</b>.

<hr>
<h1>2.0 <a name="DirectoryStructure">Directory Structure</a></h1>

<p>
  <b>Directory Structure</b>.
  The general directly layout for NuttX is very similar to the directory structure
  of the Linux kernel -- at least at the most superficial layers.
  At the top level is the main makefile and a series of sub-directories identified
  below and discussed in the following paragraphs:
</p>
<ul><pre>
.
|-- <a href="#topmakefile">Makefile</a>
|-- <a href="#DirStructDocumentation">Documentation</a>
|   `-- <i>(documentation files)</i>/
|-- <a href="#DirStructArch">arch</a>/
|   |-- <i>&lt;arch-name&gt;</i>/
|   |   |-- include/
|   |   |   |--<i>&lt;chip-name&gt;</i>/
|   |   |   |  `-- <i>(chip-specific header files)</i>
|   |   |   |--<i>&lt;other-chips&gt;</i>/
|   |   |   `-- <i>(architecture-specific header files)</i>
|   |   `-- src/
|   |       |--<i>&lt;chip-name&gt;</i>/
|   |       |  `-- <i>(chip-specific source files)</i>
|   |       |--<i>&lt;other-chips&gt;</i>/
|   |       `-- <i>(architecture-specific source files)</i>
|   `-- <i>&lt;other-architectures&gt;</i>/
|-- <a href="#DirStructConfigs">configs</a>/
|   |-- <i>&lt;board-name&gt;</i>/
|   |   |-- include/
|   |   |   `-- <i>(board-specific header files)</i>
|   |   |-- src/
|   |   |   |-- Makefile
|   |   |  `-- <i>(board-specific source files)</i>
|   |   `-- <i>(board-specific configuration files)</i>
|   `-- <i>&lt;other-boards&gt;</i>/
|-- <a href="#DirStructDrivers">drivers</a>
|   |-- Makefile/
|   `-- <i>(common driver source files)</i>
|-- <a href="#DirStructExamples">examples</a>/
|   `-- <i>(example)</i>/
|       |-- Makefile
|       `-- <i>(example source files)</i>
|-- <a href="#DirStructFs">fs</a>/
|   |-- Makefile
|   `-- <i>(fs source files)</i>
|-- <a href="#DirStructInclude">include</a>/
|   |-- <i>(standard header files)</i>
|   |-- nuttx/
|   |   `-- <i>(nuttx specific header files)</i>
|   `- sys/
|   |   `-- <i>(more standard header files)</i>
|-- <a href="#DirStructLib">lib</a>/
|   |-- Makefile
|   `-- <i>(lib source files)</i>
|-- <a href="#DirStructMm">mm</a>/
|   |-- Makefile
|   `-- <i>(mm source files)</i>
|-- <a href="#DirStructSched">sched</a>/
|   |-- Makefile
|   `-- <i>(sched source files)</i>
`-- <a href="#DirStructDrivers">tools</a>/
    |-- Makefile.mkconfig
    |-- configure.sh
    |-- mkconfig.c
    |-- mkdeps.sh
    `-- zipme
</pre></ul>

<p>
  <b>Configuration Files</b>.
  The NuttX configuration consists of:
</p>
<ul>
  <li>
    <i>Processor architecture specific files</i>.
    These are the files contained in the <code>arch/</code><i>&lt;arch-name&gt;</i><code>/</code> directory
    and are discussed in a paragraph <a href="#archdirectorystructure">below</a>.
  </li>
  <li>
    <i>Chip/SoC specific files</i>.
    Each processor processor architecture is embedded in chip or <i>System-on-a-Chip</i> (SoC) architecture.
    The full chip architecture includes the processor architecture plus chip-specific interrupt logic,
    clocking logic, general purpose I/O (GIO) logic, and specialized, internal peripherals (such as UARTs, USB, etc.).
    <p>
      These chip-specific files are contained within chip-specific sub-directories in the
      <code>arch/</code><i>&lt;arch-name&gt;</i><code>/</code> directory and are selected via
      the <code>CONFIG_ARCH_name</code> selection.
    </p>
  </li>
  <li>
    <i>Board specific files</i>.
    In order to be usable, the chip must be contained in a board environment.
    The board configuration defines additional properties of the board including such things as
    peripheral LEDs, external peripherals (such as network, USB, etc.).
    <p>
      These board-specific configuration files can be found in the
      <code>configs/</code><i>&lt;board-name&gt;</i><code>/</code> sub-directories and are discussed
      in a a paragraph <a href="#configsdirectorystructure">below</a>.
    </p>
  </li>
</ul>

<h2>2.1 <a name="DirStructDocumentation">Documentation</a></h2>

<p>
  General documentation for the NuttX OS resides in this directory.
</p>

<h2>2.2 <a name="DirStructArch">arch</a></h2>

<h3><a name="archdirectorystructure">2.2.1 Subdirectory Structure</a></h3>
<p>
  This directory contains several sub-directories, each containing
  architecture-specific logic.
  The task of porting NuttX to a new processor consists of
  add a new sudirectory under <code>arch/</code> containing logic specific
  to the new architecuture.
  The complete board port in is defined by the architecture-specific code in this
  directory (plus the board-specific configurations in the <code>config/</code>
  subdirectory).
  Each architecture must provide a subdirectory, <i>&lt;arch-name&gt;</i>
  under <code>arch/</code> with the following characteristics:
</p>
<ul><pre>
	<i>&lt;arch-name&gt;</i>/
	|-- include/
	|   |--<i>&lt;chip-name&gt;</i>/
	|   |  `-- <i>(chip-specific header files)</i>
	|   |--<i>&lt;other-chips&gt;</i>/
	|   |-- arch.h
	|   |-- irq.h
	|   |-- types.h
	|   `-- limits.h
	`-- src/
	    |--<i>&lt;chip-name&gt;</i>/
	    |  `-- <i>(chip-specific source files)</i>
	    |--<i>&lt;other-chips&gt;</i>/
	    |-- Makefile
	    `-- <i>(architecture-specific source files)</i>
</pre></ul>

<h3><a name="summaryofarchfiles">2.2.2 Summary of Files</a></h3>
<ul>
  <li>
    <code>include/</code><i>&lt;chip-name&gt;</i><code>/</code>
    This sub-directory contains chip-specific header files.
  </li>
  <li>
    <code>include/arch.h</code>:
    This is a hook for any architecture specific definitions that may
    be needed by the system.  It is included by <code>include/nuttx/arch.h</code>.
  </li>
  <li>
    <code>include/types.h</code>:
    This provides architecture/toolchain-specific definitions for
    standard types.  This file should <code>typedef</code>:
    <ul><code>
      sbyte, ubyte, uint8, boolean, sint16, uint16, sint32, uint32
    </code></ul>
    <p>and if the architecture supports 64-bit integers</p>
    <ul><code>
      sint64, uint64
    </code></ul>
    <p>
      and finally
    </p>
    <ul><code>
      irqstate_t
    </code></ul>
    <p>
      Must be defined to the be the size required to hold the interrupt
     enable/disable state.
    </p>
    <p>
      This file will be included by include/sys/types.h and be made
      available to all files.
    </p>
  </li>
  <li>
    <code>include/irq.h</code>:
    This file needs to define some architecture specific functions (usually
    inline if the compiler supports inlining) and structure.  These include:
    <ul>
      <li>
        <code>struct xcptcontext</code>:
        This structures represents the saved context of a thread.
      </li>
      <li>
        <code>irqstate_t irqsave(void)</code>:
        Used to disable all interrupts.
      </li>
      <li>
        <code>void irqrestore(irqstate_t flags)<code>:
        Used to restore interrupt enables to the same state as before <code>irqsave()</code> was called.
      </li>
    </ul>
    <p>
      This file must also define <code>NR_IRQS</code>, the total number of IRQs supported
       by the board.
    </p>
  </li>
  <li>
    <code>src/</code><i>&lt;chip-name&gt;</i><code>/</code>
    This sub-directory contains chip-specific source files.
  </li>
  <li>
    <code>src/Makefile</code>:
    This makefile will be executed to build the targets <code>src/libup.a</code> and
    <code>src/up_head.o</code>.  The <code>up_head.o</code> file holds the entry point into the system
    (power-on reset entry point, for example).  It will be used in
    the final link with <code>libup.a</code> and other system archives to generate the
    final executable.
  </li>
  <li>
    <i>(architecture-specific source files)</i>.
    The file <code>include/nuttx/arch.h</code> identifies all of the APIs that must
    be provided by the architecture specific logic.  (It also includes
    <code>arch/</code><i>&lt;arch-name&gt;</i><code>/arch.h</code> as described above).
  </li>
</ul>

<h3><a name="supportedarchitectures">2.2.3 Supported Architectures</a></h3>
<ul>
  <li><code>arch/sim</code>:
    A user-mode port of NuttX to the x86 Linux platform is available.
    The purpose of this port is primarily to support OS feature developement.
    This port does not support interrupts or a real timer (and hence no
    round robin scheduler)  Otherwise, it is complete.
  <li><code>arch/c5471</code>:
    TI TMS320C5471 (also called TMS320DM180 or just C5471).
    NuttX operates on the ARM7 of this dual core processor.
    This port is complete, verified, and included in the NuttX release 0.1.1.
  <li><code>arch/dm320</code>:
      TI TMS320DM320 (also called just DM320).
      NuttX operates on the ARM9EJS of this dual core processor.
      This port complete, verified, and included in the NuttX release 0.2.1.
  <li><code>arch/m68322</code>
      A work in progress.</li>
  <li><code>arch/pjrc-8051</code>:
    8051 Microcontroller.  This port is not quite ready for prime time.</li>
</ul>
<p>
  Other ports for the for the TI TMS320DM270 and for MIPS are in various states
  of progress
</p>

<h2>2.3 <a name="DirStructConfigs">configs</a></h2>
<p>
  The <code>configs/</code> subdirectory contains configuration data for each board.
  These board-specific configurations plus the architecture-specific configurations in
  the <code>arch/</code> subdirectory complete define a customized port of NuttX.
</p>

<h3><a name="configsdirectorystructure">2.3.1 Subdirectory Structure</a></h3>
<p>
  The configs directory contains board specific configuration files.  Each board must
  provide a subdirectory &lt;board-name&gt; under <code>configs/</code> with the following characteristics:
</p>
<ul><pre>
	<i>&lt;board-name&gt;</i>
	|-- include/
	|   `-- <i>(board-specific header files)</i>
	|-- src/
	|   |-- Makefile
	|   `-- <i>(board-specific source files)</i>
	|-- Make.defs
	|-- defconfig
	`-- setenv.sh
</pre></ul>

<h3><a name="summaryofconfigfiles">2.3.2 Summary of Files</a></h3>
<h4><a name="boardlogic">2.3.2.1 Board Specific Logic</a></h4>
<ul>
  <li>
    <code>include/</code>:
    This directory contains board specific header files.
    This directory will be linked as <code>include/arch/board</code> at configuration time
    and can be included via <code>#include &lt;arch/board/header.h&gt;</code>.
    These header file can only be included by files in <code>arch/</code><i>&lt;arch-name&gt;</i><code>/include/</code>
    and <code>arch/</code><i>&lt;arch-name&gt;</i><code>/src/</code>.
  </li>
  <li>
    <code>src/</code>:
    This directory contains board specific drivers.
    This directory will be linked as <config>arch/</code><i>&lt;arch-name&gt;</i><code>/src/board</config> at configuration
    time and will be integrated into the build system.
  </li>
  <li>
    <code>src/Makefile</code>:
    This makefile will be invoked to build the board specific drivers.
    It must support the following targets:  <code>libext$(LIBEXT)</code>, <code>clean</code>, and <code>distclean</code>.
  </li>
</ul>
<h4><a name="boardconfigfiles">2.3.2.2 Board Specific Configuration Files</a></h4>
<p>
  The <code>configs/</code><i>&lt;board-name&gt;</i><code>/</code> sub-directory holds all of the
  files that are necessary to configure Nuttx for the particular board.
  The procedure for configuring NuttX is described <a href="#configuringnuttx">below</a>,
  This paragraph will describe the contents of these configuration files.
</p>
<ul>
  <li>
    <code>Make.defs</code>: This makefile fragment provides architecture and
    tool-specific build options.  It will be included by all other
    makefiles in the build (once it is installed).  This make fragment
    should define:
    <ul>
      <li>Tools: CC, LD, AR, NM, OBJCOPY, OBJDUMP</li>
      <li>Tool options: CFLAGS, LDFLAGS</li>
    </ul>
    <p>
      When this makefile fragment runs, it will be passed TOPDIR which
      is the path to the root directory of the build.  This makefile
      fragment may include ${TOPDIR}/.config to perform configuration
      specific settings.  For example, the CFLAGS will most likely be
      different if CONFIG_DEBUG=y.
    </p>
  </li>
  <li>
    <code>defconfig</code>: This is a configuration file similar to the Linux
    configuration file.  In contains varialble/value pairs like:
    <ul>
      <li><code>CONFIG_VARIABLE</code>=value</li>
    </ul>
    <p>
      This configuration file will be used at build time:
    </p>
    <ol>
      <li>As a makefile fragment included in other makefiles, and</li>
      <li>to generate <code>include/nuttx/config.h</code> which is included by
          most C files in the system.</li>
    </ol>
  </li>
  <li>
    <code>setenv.sh</code>: This is a script that you can include that will be installed at
    the toplevel of the directory structure and can be sourced to set any
    necessary environment variables.
  </li>
</ul>

<h3><a name="supportedboards">2.3.3 Supported Boards</a></h3>
<p>
  All of the specific boards supported by NuttX are identified below.
  These the the specific <i>&lt;board-name&gt;</i>'s that may be used to configure NuttX
  as described <a href="#configuringnuttx">below</a>.
</p>
<ul>
  <li><code>configs/sim</code>:
    A user-mode port of NuttX to the x86 Linux platform is available.
    The purpose of this port is primarily to support OS feature developement.
    This port does not support interrupts or a real timer (and hence no
    round robin scheduler)  Otherwise, it is complete.</li>

  <li><code>configs/c5471evm</code>:
    This is a port to the Spectrum Digital C5471 evaluation board.  The
    C5471 is a dual core processor from TI with an ARM7TDMI general purpose
    processor and a c54 SDP.  NuttX runs on the ARM core and is built with
    with a GNU arm-elf toolchain*. This port is complete, verified, and
    included in the NuttX release.</li>

  <li><code>configs/ntosd-dm320</code>:
    This port uses the Neuros OSD with a GNU arm-elf toolchain*.
    See <a href="http://wiki.neurostechnology.com/index.php/Developer_Welcome">Neuros Wiki</a>
    for futher information.
    NuttX operates on the ARM9EJS of this dual core processor.
    STATUS: This port is code complete, verified, and included in the
    NuttX 0.2.1 release.</li>

  <li><code>configs/m68322evb</code>:
    This is a work in progress for the venerable m68322evb board from
    Motorola.</li>

  <li><code>configs/pjrc-8051</code>:
    8051 Microcontroller.  This port uses the PJRC 87C52 development system
    and the SDCC toolchain.   This port is not quite ready for prime time.</li>
</ul>

<p><small><blockquote>
  * A customized version of the <a href="http://www.buildroot.org">buildroot</a>
  is available to build these toolchains.
</blockquote></small></p>

<h2>2.4 <a name="DirStructDrivers">drivers</a></h2>

<p>
  This directory holds architecture-independent device drivers.
</p>

<h2>2.5 <a name="DirStructExamples">examples</a></h2>

<p>
  Example and test programs to build against.
</p>

<h2>2.6 <a name="DirStructFs">fs</a></h2>

<p>
  This directory contains the NuttX filesystem.
  The NuttX filesystem is very simple; it does not involve any block drivers or
  particular filesystem (like FAT or EXT2 etc.).
  The NuttX filesystem simply supports a set a filesystem APIs
  (<code>open()</code>, <code>close()</code>, <code>read()</code>, <code>write</code>, etc.)
  and a registration mechanism that allows devices drivers to a associated with <i>nodes</i>
  in a file-system-like name space.
</p>

<h2>2.7 <a name="DirStructInclude">include</a></h2>
<p>
  This directory holds NuttX header files.
  Standard header files file retained in can be included in the <i>normal</i> fashion:
</p>
<ul>
  <code>include &lt:stdio.h&gt</code><br>
  <code>include &lt;sys/types.h&gt;</code><br>
  etc.
</ul>

<h2>2.8 <a name="DirStructLib">lib</a></h2>
<p>
  This directory holds a collection of standard libc-like functions with custom
  interfaces into Nuttx.
</p>

<h2>2.9 <a name="DirStructMm">mm</a></h2>
<p>
  This is the NuttX memory manager.
</p>

<h2>2.10 <a name="DirStructSched">sched</a></h2>
<p>
  The files forming core of the NuttX RTOS reside here.
</p>

<h2>2.11 <a name="DirStructTools">tools</a></h2>
<p>
  This directory holds a collection of tools and scripts to simplify
  configuring and building NuttX.
</p>

<h2>2.12 <a name="topmakefile">Makefile</a></h2>
<p>
  The top-level <code>Makefile</code> in the <code>${TOPDIR}</code> directory contains all of the top-level control
  logic to build NuttX.
  Use of this <code>Makefile</code> to build NuttX is described <a href="#buildingnuttx">below</a>.
</p>

<hr>
<h1>3.0 <a name="configandbuild">Configuring and Building</a></h1>
<h2><a name="configuringnuttx">3.1 Configuring NuttX</a></h2>
<p>
  <b>Manual Configuration</b>.
  Configuring NuttX requires only copying the
  <a href="#boardconfigfiles">board-specific configuration files</a> into the top level directory which appears in the make files as the make variable, <code>${TOPDIR}</code>.
  This could be done manually as follows:
</p>
<ul>
  <li>Copy <code>configs/</code><i>&lt;board-name&gt;</i></code>/Make.def</code> to <code>${TOPDIR}/Make.defs</code>,<li>
  <li>Copy <code>configs/</code><i>&lt;board-name&gt;</i></code>/setenv.sh</code> to <code>${TOPDIR}/setenv.sh</code>, and</li>
  <li>Copy <code>configs/</code><i>&lt;board-name&gt;</i></code>/defconfig</code> to <code>${TOPDIR}/.config</code></li>
</ul>
<p>
  Where <i>&lt;board-name&gt;</i> is the name of one of the sub-directories of the
  NuttX <a href="#DirStructConfigs"><code>configs/</code></a> directory.
  This sub-directory name corresponds to one of the supported boards
  identified <a href="#supportedboards">above</a>.
</p>
<p>
  <b>Automated Configuration</b>.
  There is a script that automates these steps.  The following steps will
  accomplish the same configuration:
</p>
<ul><pre>
  cd tools
  ./configure.sh <i>&lt;board-name&gt;</i>
</pre></ul>

<p>
  <b>Additional Configuration Steps</b>.
  The remainder of configuration steps will be performed by <a href="#topmakefile"><code>${TOPDIR}/Makefile</code></a>
  the first time the system is built as described below.
</p>

<h2><a name="buildingnuttx">3.2 Building NuttX</a></h2>
<p>
  <b>Building NuttX</b>.
   Once NuttX has been configured as described <a href="#configuringnuttx">above</a>, it may be built as follows:
</p>
<ul><pre>
cd ${TOPDIR}
source ./setenv.sh
make
</pre></ul>
<p>
  The <code>${TOPDIR}</code> directory holds:
</p>
<ul>
  <li>The top level <a href="#topmakefile"><code>Makefile</code></a> that controls the NuttX build.
</ul>
<p>
  That directory also holds:
</p>
<ul>
  <li>The makefile fragment <a href="#boardconfigfiles"><code>.config</code></a> that describes the current configuration.</li>
  <li>The makefile fragment <a href="#boardconfigfiles"><code>Make.defs</code></a> that provides customized build targers, and</li>
  <li>The shell script <a href="#boardconfigfiles"><code>setenv.sh</code></a> that sets up the configuration environment for the build.</li>
</ul>
<p>
The <a href="#boardconfigfiles"><code>setenv.sh</code></a> contains Linux environmental settings that are needed for the build.
The specific environmental definitions are unique for each board but should include, as a minimum, updates to the <code>PATH</code> variable to include the full path to the architecture-specific toolchain identified in <a href="#boardconfigfiles"><code>Make.defs</code></a>.
The <a href="#boardconfigfiles"><code>setenv.sh</code></a> only needs to be source'ed at the beginning of a session.
The system can be re-made subsequently by just typing <code>make</code>.
</p>
<p>
  <b>First Time Make.</b>
  Additional configuration actions will be taken the first time that system is built.
  These additional steps include:
</p>
<ul>
  <li>Auto-generating the file <code>include/nuttx/config.</code> using the <code>${TOPDIR}/.config</code> file.
  <li>Creating a link to <code>${TOPDIR}/arch/</code><i>&lt;arch-name&gt;</i><code>/include</code> at <code>${TOPDIR}/include/arch</code>.
  <li>Creating a link to <code>${TOPDIR}/configs/</code><i>&lt;board-name&gt;</i><code>/include</code> at <code>${TOPDIR}/include/arch/board</code>.
  <li>Creating a link to <code>${TOPDIR}/configs/</code><i>&lt;board-name&gt;</i><code>/src</code> at <code>${TOPDIR}/arch/</code><i>&lt;arch-name&gt;</i><code>/src/board</code>
  <li>Creating make dependencies.
</ul>

<h1>4.0 <a name="ArchAPIs">Architecture APIs</a></h1>

<p>
  The file <code>include/nuttx/arch.h</code> identifies by prototype all of the APIs that must
  be provided by the architecture specific logic.
  The internal OS APIs that architecture-specific logic must
  interface with also also identified in <code>include/nuttx/arch.h</code> or in
  other header files.
</p>

<h2><a name="imports">4.1 APIs Exported by Architecture-Specific Logic to NuttX</a></h2>
<h3><a name="upinitialize">4.1.1 <code>up_initialize()</code></a></h3>

<p><b>Prototype</b>: <code>void up_initialize(void);</code></p>

<p><b>Description</b>.
  <code>up_initialize()</code> will be called once during OS
  initialization after the basic OS services have been
  initialized.  The architecture specific details of
  initializing the OS will be handled here.  Such things as
  setting up interrupt service routines, starting the
  clock, and registering device drivers are some of the
  things that are different for each processor and hardware
  platform.
</p>
<p>
  <code>up_initialize()</code> is called after the OS initialized but
  before the init process has been started and before the
  libraries have been initialized.  OS services and driver
  services are available.
</p>

<h3><a name="upidle">4.1.2 <code>up_idle()</code></a></h3>
<p><b>Prototype</b>: <code>void up_idle(void);</code></p>

<p><b>Description</b>.
  <code>up_idle()</code> is the logic that will be executed
  when their is no other ready-to-run task.  This is processor
  idle time and will continue until some interrupt occurs to
  cause a context switch from the idle task.
</p>
<p>
  Processing in this state may be processor-specific. e.g.,
  this is where power management operations might be performed.
</p>

<h3><a name="upinitialstate">4.1.3 <code>up_initial_state()</code></a></h3>
<p><b>Prototype</b>: <code>void up_initial_state(FAR _TCB *tcb);</code></p>

<p><b>Description</b>.
  A new thread is being started and a new TCB
  has been created. This function is called to initialize
  the processor specific portions of the new TCB.
</p>
<p>
  This function must setup the intial architecture registers
  and/or  stack so that execution will begin at tcb->start
  on the next context switch.
</p>

<h3><a name="upcreatestack">4.1.4 <code>up_create_stack()</code></a></h3>
<p><b>Prototype</b>: <code>STATUS up_create_stack(FAR _TCB *tcb, size_t stack_size);</code></p>

<p><b>Description</b>.
  Allocate a stack for a new thread and setup
  up stack-related information in the TCB.
</p>
<p>
  The following TCB fields must be initialized:
</p>
<ul>
  <li><code>adj_stack_size</code>: Stack size after adjustment for hardware,
    processor, etc.  This value is retained only for debug
    purposes.</li>
  <li><code>stack_alloc_ptr</code>: Pointer to allocated stack</li>
  <li><code>adj_stack_ptr</code>: Adjusted <code>stack_alloc_ptr</code> for HW.  The
    initial value of the stack pointer.
</ul>
<p>
  This API is <i>NOT</i> required if <code>CONFIG_CUSTOM_STACK</code>
  is defined.
</p>

<p><b>Inputs</b>:</p?
<ul>
  <li>
    <code>tcb</code>: The TCB of new task.
  </li>
  <li>
    <code>stack_size</code>:  The requested stack size.  At least this much
    must be allocated.
  </li>
</ul>

<h3><a name="upusestack">4.1.5 <code>up_use_stack()</code></a></h3>
<p><b>Prototype</b>: 
  <code>STATUS up_use_stack(FAR _TCB *tcb, FAR void *stack, size_t stack_size);</code>
</p>

<p><b>Description</b>.
  Setup up stack-related information in the TCB
  using pre-allocated stack memory.
</p>
<p>
  The following TCB fields must be initialized:
</p>
<ul>
  <li><code>adj_stack_size</code>: Stack size after adjustment for hardware,
    processor, etc.  This value is retained only for debug
    purposes.</li>
  <li><code>stack_alloc_ptr</code>: Pointer to allocated stack</li>
  <li><code>adj_stack_ptr</code>: Adjusted <code>stack_alloc_ptr</code> for HW.  The
    initial value of the stack pointer.
</ul>
<p>
  This API is <i>NOT</i> required if <code>CONFIG_CUSTOM_STACK</code>
  is defined.
</p>

<p><b>Inputs:</b></p>
<ul>
  <li>
    <code>tcb</code>: The TCB of new task.
  </li>
  <li>
    <code>stack_size</code>:  The allocated stack size.
  </li>
</ul>

<h3><a name="upreleasestack">4.1.6 <code>up_release_stack()</code></a></h3>
<p><b>Prototype</b>: <code>void up_release_stack(FAR _TCB *dtcb);</code></p>

<p><b>Description</b>.
  A task has been stopped. Free all stack
  related resources retained int the defunct TCB.
</p>
<p>
  This API is <i>NOT</i> required if <code>CONFIG_CUSTOM_STACK</code>
  is defined.
</p>

<h3><a name="upunblocktask">4.1.7 <code>up_unblock_task()</code></a></h3>
<p><b>Prototype</b>: <code>void up_unblock_task(FAR _TCB *tcb);</code></p>

<p><b>Description</b>.
  A task is currently in an inactive task list
  but has been prepped to execute.  Move the TCB to the
  ready-to-run list, restore its context, and start execution.
</p>
<p>
  This function is called only from the NuttX scheduling
  logic.  Interrupts will always be disabled when this
  function is called.
</p>

<p><b>Inputs</b>:
<ul>
  <li><code>tcb</code>: Refers to the tcb to be unblocked.  This tcb is
    in one of the waiting tasks lists.  It must be moved to
    the ready-to-run list and, if it is the highest priority
    ready to run taks, executed.
  </li>
</ul>

<h3><a name="upblocktask">4.1.8 <code>up_block_task()</code></a></h3>
<p><b>Prototype</b>: <code>void up_block_task(FAR _TCB *tcb, tstate_t task_state);</code></p>

<p><b>Description</b>.
  The currently executing task at the head of
  the ready to run list must be stopped.  Save its context
  and move it to the inactive list specified by task_state.

  This function is called only from the NuttX scheduling
  logic.  Interrupts will always be disabled when this
  function is called.

<p><b>Inputs:</b></p>
<ul>
  <li><code>tcb</code>: Refers to a task in the ready-to-run list (normally
    the task at the the head of the list).  It most be
    stopped, its context saved and moved into one of the
    waiting task lists.  It it was the task at the head
    of the ready-to-run list, then a context to the new
    ready to run task must be performed.
  </li>
  <li><code>task_state</code>: Specifies which waiting task list should be
    hold the blocked task TCB.
  </li>
</ul>

<h3><a name="upreleasepending">4.1.9 <code>up_release_pending()</code></a></h3>
<p><b>Prototype</b>: <code>void up_release_pending(void);</code></p>

<p><b>Description</b>.
  When tasks become ready-to-run but cannot run because pre-emption
  is disabled, they are placed into a pending task list.
  This function releases and makes ready-to-run all of the tasks that have
  collected in the pending task list.  This can cause a
  context switch if a new task is placed at the head of
  the ready to run list.
</p>
<p>
  This function is called only from the NuttX scheduling logic when
  pre-emption is re-enabled.  Interrupts will always be disabled when this
  function is called.
</p>

<h3><a name="upreprioritizertr">4.1.10 <code>up_reprioritize_rtr()</code></a></h3>
<p><b>Prototype</b>: <code>void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority);</code></p>

<p><b>Description</b>.
  Called when the priority of a running or
  ready-to-run task changes and the reprioritization will 
  cause a context switch.  Two cases:
</p>
<ol>
  <li>
    The priority of the currently running task drops and the next
    task in the ready to run list has priority.
  </li>
  <li>
    An idle, ready to run task's priority has been raised above the
    the priority of the current, running task and it now has the
    priority.
  </li>
</ol>
<p>
  This function is called only from the NuttX scheduling
  logic.  Interrupts will always be disabled when this
  function is called.
</p>

<p><b>Inputs:</b></p>
<ul>
  <li>
    <code>tcb</code>: The TCB of the task that has been reprioritized
  </li>
  <li>
    <code>priority</code>: The new task priority
  </li>
</ul>

<h3><a name="_exit">4.1.11 <code>_exit()</code></a></h3>
<p><b>Prototype</b>: <code>void _exit(int status) noreturn_function;</code></p>

<p><b>Description</b>.
  This function causes the currently executing task to cease
  to exist.  This is a special case of task_delete().
</p>
<p>
  Unlike other UP APIs, this function may be called
  directly from user programs in various states.  The
  implementation of this function should diable interrupts
  before performing scheduling operations.
</p>

<h3><a name="upassert">4.1.12 <code>up_assert()</code></a></h3>
<p><b>Prototype</b>:<br>
  <code>void up_assert(FAR const ubyte *filename, int linenum);</code></br>
  <code>void up_assert_code(FAR const ubyte *filename, int linenum, int error_code);</code></br>
</p>

<p><b>Description</b>.
  Assertions may be handled in an architecture-specific
  way.
</p>

<h3><a name="upschedulesigaction">4.1.13 <code>up_schedule_sigaction()</code></a></h3>
<p><b>Prototype</b>:
  <code>void up_schedule_sigaction(FAR _TCB *tcb, sig_deliver_t sigdeliver);</code>
</p>

<p><b>Description</b>.
  This function is called by the OS when one or more
  signal handling actions have been queued for execution.
  The architecture specific code must configure things so
  that the 'igdeliver' callback is executed on the thread
  specified by 'tcb' as soon as possible.
</p>
<p>
  This function may be called from interrupt handling logic.
</p>
<p>
  This operation should not cause the task to be unblocked
  nor should it cause any immediate execution of sigdeliver.
  Typically, a few cases need to be considered:
</p>
<ol>
  <li>
    This function may be called from an interrupt handler
    During interrupt processing, all xcptcontext structures
    should be valid for all tasks.  That structure should
    be modified to invoke sigdeliver() either on return
    from (this) interrupt or on some subsequent context
    switch to the recipient task.
  </li>
  <li>
    If not in an interrupt handler and the tcb is NOT
    the currently executing task, then again just modify
    the saved xcptcontext structure for the recipient
    task so it will invoke sigdeliver when that task is
    later resumed.
  </li>
  <li>
    If not in an interrupt handler and the tcb IS the
    currently executing task -- just call the signal
    handler now.
  </li>
</ol>
<p>
  This API is <i>NOT</i> required if <code>CONFIG_DISABLE_SIGNALS</code>
  is defined.
</p>

<h3><a name="upallocateheap">4.1.14 <code>up_allocate_heap()</code></a></h3>
<p><b>Prototype</b>: <code>void up_allocate_heap(FAR void **heap_start, size_t *heap_size);</code></p>

<p><b>Description</b>.
  The heap may be statically allocated by
  defining CONFIG_HEAP_BASE and CONFIG_HEAP_SIZE.  If these
  are not defined, then this function will be called to
  dynamically set aside the heap region.
</p>
<p>
  This API is <i>NOT</i> required if <code>CONFIG_HEAP_BASE</code>
  is defined.
</p>

<h3><a name="upinterruptcontext">4.1.15 <code>up_interrupt_context()</code></a></h3>
<p><b>Prototype</b>: <code>boolean up_interrupt_context(void)</code></p>

<p><b>Description</b>.
  Return TRUE is we are currently executing in
  the interrupt handler context.
</p>

<h3><a name="updisableirq">4.1.16 <code>up_disable_irq()</code></a></h3>
<p><b>Prototype</b>: <code>void up_disable_irq(int irq);</code></p>

<p><b>Description</b>.
  Disable the IRQ specified by 'irq'
</p>

<h3><a name="upenableirq">4.1.17 <code>up_enable_irq()</code></a></h3>
<p><b>Prototype</b>: <code>void up_enable_irq(int irq);</code></p>

<p><b>Description</b>.
  Enable the IRQ specified by 'irq'
</p>

<h3><a name="upputc">4.1.18 <code>up_putc()</code></a></h3>

<p><b>Prototype</b>: <code>int up_putc(int ch);</code></p>
<p><b>Description</b>.
  This is a debug interface exported by the architecture-specific logic.
  Output one character on the console
<p>
  This API is <i>NOT</i> required if <code>CONFIG_HEAP_BASE</code>
  is defined.
</p>

<h2><a name="exports">4.2 APIs Exported by NuttX to Architecture-Specific Logic</a></h2>
<p>
  These are standard interfaces that are exported by the OS
  for use by the architecture specific logic.
</p>

<h3><a name="osstart">4.2.1 <code>os_start()</code></a></h3>
<p>
  <b><i>To be provided</i></b>
</p>

<h3><a name="listmgmt">4.2.2 OS List Management APIs</a></h3></h3>
<p>
  <b><i>To be provided</i></b>
</p>

<h3><a name="schedprocesstimer">4.2.3 <code>sched_process_timer()</code></a></h3>
<p><b>Prototype</b>: <code>void sched_process_timer(void);</code></p>

<p><b>Description</b>.
  This function handles system timer events.
  The timer interrupt logic itself is implemented in the
  architecture specific code, but must call the following OS
  function periodically -- the calling interval must be
  <code>MSEC_PER_TICK</code>.
</p>

<h3><a name="irqdispatch">4.2.4 <code>irq_dispatch()</code></a></h3>
<p><b>Prototype</b>: <code>void irq_dispatch(int irq, FAR void *context);</code></p>

<p><b>Description</b>.
  This function must be called from the achitecture-
  specific logic in order to dispaly an interrupt to
  the appropriate, registered handling logic.
</p>

<h1><a name="apndxconfigs">Appendix A:  NuttX Configuration Settings</a></h1>

<p>
  The following variables are recognized by the build (you may
  also include architecture-specific settings).
</p>

<h2>Architecture selection</h2>

<ul>
  <li><code>CONFIG_ARCH</code>: identifies the arch subdirectory
  <li><code>CONFIG_ARCH_name</code>: for use in C code
</ul>

<h2>General OS setup</h2>

<ul>
  <li>
    <code>CONFIG_EXAMPLE</code>: identifies the subdirectory in examples
    that will be used in the build.
  </li>
  <li>
    <code>CONFIG_DEBUG</code>: enables built-in debug options
  </li>
  <li>
    <code>CONFIG_DEBUG_VERBOSE</code>: enables verbose debug output
  </li>
  <li>
    <code>CONFIG_HAVE_LOWPUTC</code>: architecture supports low-level, boot
    time console output
  </li>
  <li>
    <code>CONFIG_MM_REGIONS</code>: If the architecture includes multiple
    regions of memory to allocate from, this specifies the
    number of memory regions that the memory manager must
    handle and enables the API mm_addregion(start, end);
  </li>
  <li>
    <code>CONFIG_RR_INTERVAL</code>: The round robin timeslice will be set
    this number of milliseconds;  Round robin scheduling can
    be disabled by setting this value to zero.
  </li>
  <li>
    <code>CONFIG_SCHED_INSTRUMENTATION</code>: enables instrumentation in 
    scheduler to monitor system performance
  </li>
  <li>
    <code>CONFIG_TASK_NAME_SIZE</code>: Spcifies that maximum size of a
    task name to save in the TCB.  Useful if scheduler
    instrumentation is selected.  Set to zero to disable.
  </li>
  <li>
    <code>CONFIG_START_YEAR, CONFIG_START_MONTH, CONFIG_START_DAY -
    Used to initialize the internal time logic.
  </li>
  <li>
    <code>CONFIG_JULIAN_TIME</code>: Enables Julian time conversions
  </li>
  <li>
    <code>CONFIG_DEV_CONSOLE</code>: Set if architecture-specific logic
    provides /dev/console.  Enables stdout, stderr, stdin.
  </li>
</ul>

<p>
  The following can be used to disable categories of APIs supported
  by the OS.  If the compiler supports weak functions, then it
  should not be necessary to disable functions unless you want to
  restrict usage of those APIs.
</p>
<p>
  There are certain dependency relationships in these features.
</p>
<ul>
  <li>
    <code>mq_notify()</code> logic depends on signals to awaken tasks
    waiting for queues to become full or empty.
  </li>
  <li>
    <code>pthread_condtimedwait()</code> depends on signals to wake
    up waiting tasks.
  </li>
</ul>

<ul>
    <code>CONFIG_DISABLE_CLOCK</code>, <code>CONFI_DISABLE_POSIX_TIMERS</code>, <code>CONFIG_DISABLE_PTHREAD</code>,
    <code>CONFIG_DISABLE_SIGNALS</code>, <code>CONFIG_DISABLE_MQUEUE</code>,
</ul>

<h2>Miscellaneous libc settings</h2>

<ul>
  <li>
    <code>CONFIG_NOPRINTF_FIELDWIDTH</code>: sprintf-related logic is a
    little smaller if we do not support fieldwidthes
  </li>
</ul>

<h2>Allow for architecture optimized implementations</h2>

<p>
  The architecture can provide optimized versions of the
  following to improve sysem performance.
</p>

<ul>
<p>
  <code>CONFIG_ARCH_MEMCPY</code>, <code>CONFIG_ARCH_MEMCMP</code>, <code>CONFIG_ARCH_MEMMOVE</code>,
  <code>CONFIG_ARCH_MEMSET</code>, <code>CONFIG_ARCH_STRCMP</code>, <code>CONFIG_ARCH_STRCPY</code>,
  <code>CONFIG_ARCH_STRNCPY</code>, <code>CONFIG_ARCH_STRLEN</code>, <code>CONFIG_ARCH_BZERO</code>,
  <code>CONFIG_ARCH_KMALLOC</code>, <code>CONFIG_ARCH_KZMALLOC</code>, <code>ONFIG_ARCH_KFREE</code>,
</p>
</ul>

<h2>Sizes of configurable things (0 disables)</h2>

<ul>
  <li>
    <code>CONFIG_MAX_TASKS</code>: The maximum number of simultaneously
    active tasks.  This value must be a power of two.
  </li>
  <li>
    <code>CONFIG_NPTHREAD_KEYS</code>: The number of items of thread-
    specific data that can be retained
  </li>
  <li>
    <code>CONFIG_NFILE_DESCRIPTORS</code>: The maximum number of file
    descriptors (one for each open)
  </li>
  <li>
    <code>CONFIG_NFILE_STREAMS</code>: The maximum number of streams that
    can be fopen'ed
  </li>
  <li>
    <code>CONFIG_NAME_MAX</code>: The maximum size of a file name.
  </li>
  <li>
    <code>CONFIG_STDIO_BUFFER_SIZE</code>: Size of the buffer to allocate
    on fopen. (Only if CONFIG_NFILE_STREAMS > 0)
  </li>
  <li>
    <code>CONFIG_NUNGET_CHARS</code>: Number of characters that can be
    buffered by ungetc() (Only if CONFIG_NFILE_STREAMS > 0)
  </li>
  <li>
    <code>CONFIG_PREALLOC_MQ_MSGS</code>: The number of pre-allocated message
    structures.  The system manages a pool of preallocated
    message structures to minimize dynamic allocations
  </li>
  <li>
    <code>CONFIG_MQ_MAXMSGSIZE</code>: Message structures are allocated with
    a fixed payload size given by this settin (does not include
    other message structure overhead.
  </li>
  <li>
    <code>CONFIG_PREALLOC_WDOGS</code>: The number of pre-allocated watchdog
    structures.  The system manages a pool of preallocated
    watchdog structures to minimize dynamic allocations
  </li>
</ul>

<h2>Stack and heap information</h2>

<ul>
  <li>
    <code>CONFIG_BOOT_FROM_FLASH</code>: Some configurations support XIP
    operation from FLASH.
  </li>
  <li>
    <code>CONFIG_STACK_POINTER</code>: The initial stack pointer
  </li>
  <li>
    <code>CONFIG_PROC_STACK_SIZE</code>: The size of the initial stack
  </li>
  <li>
    <code>CONFIG_PTHREAD_STACK_MIN</code>: Minimum pthread stack size
  </li>
  <li>
    <code>CONFIG_PTHREAD_STACK_DEFAULT</code>: Default pthread stack size
  </li>
  <li>
    <code>CONFIG_HEAP_BASE</code>: The beginning of the heap
  </li>
  <li>
    <code>CONFIG_HEAP_SIZE</code>: The size of the heap
  </li>
</ul>

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