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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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45 lines
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==========
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Interrupts
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==========
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How NuttX takes an interrupt, what an interrupt handler may and may not do,
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and how code protects itself from one. The code lives in ``sched/irq/``,
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with the vector table and the entry sequence in
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``arch/<arch>/src/``.
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On most architectures an interrupt handler runs with interrupts disabled --
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nesting is the exception rather than the rule, and
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:doc:`/guides/concurrency/nestedinterrupts` covers it -- and on every
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architecture the handler cannot block. That is the whole reason the rest of
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this section exists: anything that has to wait, allocate or take a lock has
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to be handed off, which is what :doc:`bottom halves <bottomhalf_interrupt>`
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and the work queues are for.
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.. figure:: interrupt_flow.svg
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:align: center
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:width: 100%
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:alt: An interrupt is vectored by the architecture entry code, dispatched
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to the driver handler which does only what cannot wait, and the
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rest is handed to a work queue thread; on return the scheduler may
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switch to a different thread.
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From the peripheral asserting the line to the return, and where the work
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that cannot be done in a handler goes instead.
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The last step is the one that surprises people: returning from an interrupt
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does not necessarily return to the thread that was interrupted. A handler
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often makes a higher-priority thread ready -- that is usually the whole
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point -- and NuttX switches to it before the interrupted thread runs again.
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For protecting a section of code, note that disabling interrupts and
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locking pre-emption are not the same choice and do not cost the same. See
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:doc:`critical_sections` for the difference, and
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:doc:`/os/scheduling/preemption_latency` for what each one does to response
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time.
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.. toctree::
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:maxdepth: 1
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interrupt_controls.rst
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critical_sections.rst
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bottomhalf_interrupt.rst
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