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f6ecf80ebb
The documentation grew one page at a time, so the tree follows the
history of who wrote what and not the shape of NuttX. Scheduling is
spread over three places, a driver page can sit above the subsystem
that owns it, and the front page lists everything at the same level.
That is a lot to face when all you want to know is where the scheduler
lives.
This change files every page under the code it describes. It is a move,
not a rewrite: outside the ten pages named below, every page keeps the
text that is already in master, and no page's text is deleted.
What it does:
* Groups the table of contents into nine chapters.
* Moves the OS subsystems under os/: scheduling, memory, drivers,
filesystem, networking, IPC, interrupts, libs, time.
* Renames the platform pages to the names the source tree uses, and
derives their tags from the tree instead of by hand.
* Splits guides/ by subject.
* Adds Documentation/redirects.py, with a rule for every page that left
its old path, so old URLs keep working. The redirect page also carries
a link's #anchor across to the new page.
Ten pages have text that is new or rewritten. Nine of them are the
landing page of a chapter, which has to exist for the new structure:
index the front page
os/index OS Design
os/scheduling/index Scheduling
os/interrupts/index Interrupts
os/ipc/index IPC
os/time/index Time and timers
about/index About
developing/index Developing NuttX
ReleaseNotes/index Release notes
The tenth is os/libs/libbuiltin, the only page here with technical
content: libs/libbuiltin/ had no page at all. Five SVG diagrams come
with these pages, hand-written XML with no editor metadata.
Nothing outside Documentation/ is touched.
How it was checked:
* Sphinx builds with -W: no warnings, and no document left outside a
toctree.
* A script, offered in the PR, proves the narrow claim this rests on.
For every page outside the ten named above it erases what a move
touches -- link target, path, tag line, toctree block, table border --
from the whole old text and the whole new text, and requires the two
to be byte for byte identical. It also requires every sentence of a
deleted page to turn up somewhere, and every page that left its old
path to have a redirect, from a URL that existed, to where its content
went. It exits non-zero and names the page if any of that is not true,
and it tests added pages too, so forgetting to declare one cannot make
it pass.
* An independent audit checked 133 factual claims on these ten pages
against the tree, one shell command per claim: 130 confirmed, 1
refuted and fixed here, 2 not checkable.
* tools/checkpatch.sh is clean over the range.
The diff is large because moving a page changes every link that points
to it. Most of it is pure renames, and board pages that gained one tag
line.
Assisted-by: Claude:claude-opus-5
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=========
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OS Design
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=========
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How NuttX is put together, subsystem by subsystem. The sections follow the source
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tree: what lives under ``sched/`` is described in :doc:`scheduling/index`,
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what lives under ``fs/`` in :doc:`filesystem/index`, under ``drivers/`` in
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:doc:`drivers/index`, and so on. Each subsystem is described once, going
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from what it is, to how it works, to the interfaces it offers.
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For the POSIX interface an application sees, go to
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:doc:`/reference/user/index` instead. That is a different question -- what
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you may call -- and it has its own section.
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.. figure:: system_map.svg
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:align: center
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:width: 100%
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:alt: The layers of NuttX, from applications down through the C library
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and the system call boundary to the kernel subsystems, the device
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drivers, and the architecture, chip and board code.
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Where each section of this documentation sits in the system, and which
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directory of the source tree it describes.
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Build modes
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===========
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Before reading any subsystem page it is worth knowing which **build mode**
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you are in, because it decides whether there is a boundary between your
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application and the kernel at all. The Kconfig choice that selects it is
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called *Memory organization*, under *Build Configuration*.
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.. figure:: build_modes.svg
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:align: center
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:width: 100%
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:alt: The same call to write() under the three build modes: a function
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call in a flat build, a system call across an MPU boundary in a
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protected build, and a system call into a separate address space in
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a kernel build.
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The same ``write()`` under ``CONFIG_BUILD_FLAT``,
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``CONFIG_BUILD_PROTECTED`` and ``CONFIG_BUILD_KERNEL``.
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A flat build is one program: calling ``write()`` is a function call, and an
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application bug can corrupt the kernel. A protected build is two blobs, one
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privileged and one unprivileged, with an MPU between them, so the same call
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becomes a system call; no address mapping is performed, so the two blobs
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still share one set of addresses. A kernel build gives each process its own
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address environment through an MMU. That is what ``fork()`` needs -- the
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child gets its own copy of the parent's memory *at the same virtual
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addresses* -- and what ``CONFIG_PAGING`` requires as well.
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Much of what the pages below say depends on this choice, which is why it is
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worth settling first. That is the short version; the page below is the long
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one, and takes each mode in turn, with on-demand paging and address
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environments described alongside them.
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.. toctree::
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:maxdepth: 1
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build_modes.rst
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The kernel
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==========
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.. toctree::
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:maxdepth: 1
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scheduling/index.rst
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ipc/index.rst
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concurrency/index.rst
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time/index.rst
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interrupts/index.rst
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memory/index.rst
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Device drivers
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==============
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By far the largest part of the OS: ``drivers/`` holds 59 subdirectories, of
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which storage is five. Everything a board talks to goes through here.
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.. toctree::
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:maxdepth: 1
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drivers/index.rst
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File systems and networking
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===========================
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.. toctree::
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:maxdepth: 1
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filesystem/index.rst
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networking/index.rst
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Running programs
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================
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.. toctree::
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:maxdepth: 1
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binfmt/index.rst
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syscall.rst
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libs/index.rst
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Media and security
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==================
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.. toctree::
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:maxdepth: 1
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graphics/index.rst
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audio/index.rst
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video.rst
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crypto.rst
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wireless.rst
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Portability
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===========
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.. toctree::
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:maxdepth: 1
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arch/index.rst
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openamp.rst
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Reference
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=========
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.. toctree::
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:maxdepth: 1
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nuttx.rst
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app_vs_os.rst
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conventions.rst
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notifier.rst
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