102 lines
4.5 KiB
ReStructuredText
102 lines
4.5 KiB
ReStructuredText
===============
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Host Side Tools
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===============
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``bitmap_converter.py`` NxWidgets
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=================================
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This script converts from any image type supported by Python imaging library to
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the RLE-encoded format used by NxWidgets.
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RLE (Run Length Encoding) is a very simply encoding that compress quite well
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with certain kinds of images: Images that that have many pixels of the same
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color adjacent on a row (like simple graphics). It does not work well with
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photographic images.
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But even simple graphics may not encode compactly if, for example, they have
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been resized. Resizing an image can create hundreds of unique colors that may
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differ by only a bit or two in the RGB representation. This "color smear" is the
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result of pixel interpolation (and might be eliminated if your graphics software
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supports resizing via pixel replication instead of interpolation).
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When a simple graphics image does not encode well, the symptom is that the
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resulting RLE data structures are quite large. The palette structure, in
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particular, may have hundreds of colors in it. There is a way to fix the graphic
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image in this case. Here is what I do (in fact, I do this on all images prior to
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conversion just to be certain):
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- Open the original image in GIMP.
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- Select the option to select the number of colors in the image.
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- Pick the smallest number of colors that will represent the image faithfully.
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For most simple graphic images this might be as few as 6 or 8 colors.
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- Save the image as PNG or other lossless format (NOT jpeg).
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- Then generate the image.
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``mkromfsimg.sh``
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=================
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**Q**: Why are there two versions of the script ``mkromfsimg.sh``, one in
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``apps/tools`` and one in ``nuttx/tools``.
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**A**: The version of ``mkromfsimg.sh`` in ``nuttx/tools`` is a generic
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tool to simplify creation of ROMFS file system from any directory contain
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content that you would like to access within the the target.
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The version in ``apps/tools``, on the other hand, has a very special purpose.
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It is part of the support that can be used in the KERNEL build mode.
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Processes and Programs in the KERNEL Build
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------------------------------------------
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In the kernel build, there are no tasks. There are only processes and all
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code lives in its own, private address space.
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See :doc:`/implementation/processes_vs_tasks`.
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One consequence of that is that functions like ``task_create()`` and friends
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cannot be used in the KERNEL build mode. Instead, all processes must be loaded
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into a virtual address space from an ELF or NxFLAT file residing in the file
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system. ROMFS is one of many file system, but one that is particularly usable
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for this purpose in deeply embedded systems.
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KERNEL Build Differences
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------------------------
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In the FLAT and PROTECTED build mode all applications are built into a single
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BLOB, so every symbol must have a unique name to avoid name collisions.
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In the KERNEL build mode, all applications are built at separately linked
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programs that reside in a file system. The entry point to ALL programs is the
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function ``main()``.
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apps/bin
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--------
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When you build the ``apps/`` programs in FLAT or PROTECTED modes, all of the
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object files are put into an archive apps/libapps.a which is, eventually,
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copied to ``nuttx/libs`` and the BLOB is created by linking NuttX archives
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with ``lib/libapps.a``.
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But when you build the ``apps/`` programs in the KERNEL mode, the directory
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``apps/bin`` is created by the top-level apps/Makefile. Each source file is
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compiled, but the object files are not added to ayn archive. Instead, the
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object files are linked into a separate compiled and linked program. Each program
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is then installed at ``apps/bin``.
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apps/tools/mkromfsimg.sh
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------------------------
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When the ``apps/`` kernel build is complete, all of the programs have been installed
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in ``apps/bin``. That is where ``apps/tools/mkromfsimg.sh`` file comes into to play.
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It takes all of the programs in apps/bin and creates a ROMFS file system image
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containing all of the applications. That ROMFS file system image is built into
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the kernel.
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Application Initialization
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--------------------------
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At run time, when the kernel boots, it will mount that ROMFS file system at ``/bin``.
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In the FLAT build mode, the OS boot logic calls ``task_create()`` to start the initial
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task you have configured with ``CONFIG_INIT_ENTRYPOINT``. But in the KERNEL build, something
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different happens. ``CONFIG_INIT_ENTRYPOINT`` is not used. Instead, ``CONFIG_INIT_FILEPATH``
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is used. This will be the name of the program to stared in ``/bin`` to bring up the system.
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