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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
68 lines
2.5 KiB
ReStructuredText
68 lines
2.5 KiB
ReStructuredText
==================
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``fb`` Framebuffer
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==================
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This application is a simple demonstration which serves to test the
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:doc:`framebuffer character driver
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</os/graphics/framebuffer_char_driver>`.
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The program interacts with the framebuffer through the interfaces described in
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the linked page in order to render a very simple image consisting of 6
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concentric, colourful rectangles. Note that between each rectangle, the program
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sleeps for 500 milliseconds. Rectangle are drawn from outermost to innermost, in
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descending size.
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.. figure:: fb-image.jpg
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:figwidth: 80%
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:align: center
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:alt: The Pinephone displaying concentric, colourful rectangles after running the ``fb`` example.
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The image displayed by the ``fb`` example, shown on the Pinephone. Credit to
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Lup Yuen Lee.
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.. warning::
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The application renders directly to the framebuffer provided by the character
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driver. On some devices, the entire rendering operation may not be complete
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in time for the video synchronization, causing screen tearing or skips. This
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is the case for the :doc:`Raspberry Pi 4B
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</platforms/arm64/bcm2711/boards/raspberrypi-4b/index>`, and the results can
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be seen below.
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.. figure:: fb-skip.png
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:figwidth: 40%
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:align: center
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:alt: The framebuffer example output, but with skipped pixels.
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The framebuffer example output, but with skipped pixels.
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Skipping issues like this one can generally be avoided by rendering to a
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separate buffer first, and then copying that buffer to the framebuffer in one
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operation.
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Feature support
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---------------
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The application ignores the pixel format provided by the framebuffer character
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driver, and only inspects the 'bits per pixel' (depth) field. Currently, only
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the following bits per pixel are supported (with the corresponding formats
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assumed):
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* 1: Monochrome
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* 8: RGB_332
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* 16: RGB_565
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* 24: RGB
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* 32: ARGB
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The program supports different features depending on the characteristics of the
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framebuffer driver. If the framebuffer requires ``FB_UPDATE``, this example
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behaves accordingly.
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If the framebuffer supports ``FB_OVERLAY``, then the application also supports
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getting and displaying the overlay information.
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If the virtual y resolution is double that of the y resolution when the
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framebuffer is initially queried, the application will attempt to use
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double-buffer rendering by fetching a second framebuffer corresponding to the
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``display + 1``, where ``display`` is the display number that was associated
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with the first framebuffer.
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