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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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Using Kernel Threads
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====================
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.. warning::
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Migrated from:
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https://cwiki.apache.org/confluence/display/NUTTX/Using+Kernel+Threads
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Build Configurations
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====================
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NuttX can be built in three different configurations: (1) as a FLAT build where
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all of the code resides in a common address space, (2) as a PROTECTED build
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where a memory protection unit (MPU) is used to separate the memory into
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privileged memory for the OS and unprivileged memory for all applications,
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or (3) as a KERNEL build where a memory management unit (MMU) is used place
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the OS in a privileged address space and to place to task (or process) in its
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own virtual address space.
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In the last two configurations, applications reside outside of the OS address
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space and in all configurations applications do not have have access to any
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internal resources of the OS.
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More information about these build configurations can be found on `the Memory
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Configuration Wiki page <https://cwiki.apache.org/confluence/display/NUTTX/Memory+Configurations>`_.
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Thread Types
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============
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NuttX supports three classes of threads: tasks, pthreads, and kernel threads.
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tasks and pthreads are both application threads and are distinguished by some
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usage semantics and by their hierarchical relationship. tasks are created via
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several different mechanisms: ``task_create()``, ``task_spawn()``, ``execv()``,
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``posix_spawn()``, and others. Tasks may then create pthreads using
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``pthread_create()``.
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More information about tasks and pthreads can be found on the
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`NuttX Tasking <https://cwiki.apache.org/confluence/display/NUTTX/NuttX+Tasking>`_
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Wiki page.
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Kernel Threads
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==============
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Kernel threads are really like tasks except that they run inside the operating
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system and are started with ``kthread_create()`` which is prototyped in
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``include/nuttx/kthread.h``. The differ from tasks in that (1) in PROTECTED and
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KERNEL builds, they have full supervisor privileges, and (2) they have full
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access to all internal OS resources.
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In order to build the task into the OS as a kernel thread, you simply have to:
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(1) place the kernel thread code in your board source code directory, and (2)
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start it with ``kthread_create()`` in your board bring-up logic. There a few
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examples of this in the NuttX source tree. Here is one:
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`https://github.com/apache/nuttx/blob/master/boards/arm/stm32f1/viewtool-stm32f107/src/stm32_highpri.c <https://github.com/apache/nuttx/blob/master/boards/arm/stm32f1/viewtool-stm32f107/src/stm32_highpri.c>`_
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So that is another trick that you can use to architecture optimal solutions:
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Create parts of your applications as kernel threads: They need to reside in
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your board/src directory and the need to be started with ``kthread_create()`` in
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your board bring-up logic. And that is it.
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