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zephyr/samples/basic/minimal
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Keith Packard 0b90fd5adf samples, tests, boards: Switch main return type from void to int 
As both C and C++ standards require applications running under an OS to
return 'int', adapt that for Zephyr to align with those standard. This also
eliminates errors when building with clang when not using -ffreestanding,
and reduces the need for compiler flags to silence warnings for both clang
and gcc.

Most of these changes were automated using coccinelle with the following
script:

@@
@@
- void
+ int
main(...) {
	...
-	return;
+	return 0;
	...
}

Approximately 40 files had to be edited by hand as coccinelle was unable to
fix them.

Signed-off-by: Keith Packard <keithp@keithp.com>
 		2023-04-14 07:49:41 +09:00
..
src
…
CMakeLists.txt
…
README.rst
…
arm.conf
…
common.conf
…
mt.conf
…
no-mt.conf
…
no-preempt.conf
…
no-timers.conf
…
prj.conf
…
sample.yaml
…
x86.conf
…

README.rst 

.. _minimal_sample:

Minimal footprint
#################

Overview
********

This sample provides an empty ``main()`` and various configuration files that
can be used to measure Zephyr's minimal ROM footprint in different
configurations.

The following configuration files are available:

* :file:`mt.conf`: Enable multithreading
* :file:`no-mt.conf`: Disable multithreading
* :file:`no-preempt.conf`: Disable preemption
* :file:`no-timers.conf`: Disable timers
* :file:`arm.conf`: Arm-specific disabling of features

Building and measuring ROM size
*******************************

The following combinations are suggested for comparing ROM sizes in different
configurations. They all target the :ref:`reel_board` (Arm Aarch32 architecture).

* Multithreading enabled

  * Reference ROM size: 7-8KB

  .. zephyr-app-commands::
     :zephyr-app: samples/basic/minimal
     :host-os: unix
     :board: reel_board
     :build-dir: reel_board/mt/
     :conf: "common.conf mt.conf arm.conf"
     :goals: rom_report
     :compact:

* Multithreading enabled, no preemption

  * Reference ROM size: 7-8KB

  .. zephyr-app-commands::
     :zephyr-app: samples/basic/minimal
     :host-os: unix
     :board: reel_board
     :build-dir: reel_board/mt-no-preempt/
     :conf: "common.conf mt.conf no-preempt.conf arm.conf"
     :goals: rom_report
     :compact:

* Multithreading enabled, no preemption, timers disabled

  * Reference ROM size: 3-4KB

  .. zephyr-app-commands::
     :zephyr-app: samples/basic/minimal
     :host-os: unix
     :board: reel_board
     :build-dir: reel_board/mt-no-preempt-no-timers/
     :conf: "common.conf mt.conf no-preempt.conf no-timers.conf arm.conf"
     :goals: rom_report
     :compact:

* Multithreading disabled, timers enabled

  * Reference ROM size: 4-5KB

  .. zephyr-app-commands::
     :zephyr-app: samples/basic/minimal
     :host-os: unix
     :board: reel_board
     :build-dir: reel_board/no-mt/
     :conf: "common.conf no-mt.conf arm.conf"
     :goals: rom_report
     :compact:

* Multithreading disabled, timers disabled

  * Reference ROM size: 2-3KB

  .. zephyr-app-commands::
     :zephyr-app: samples/basic/minimal
     :host-os: unix
     :board: reel_board
     :build-dir: reel_board/no-mt-no-timers/
     :conf: "common.conf no-mt.conf no-timers.conf arm.conf"
     :goals: rom_report
     :compact: