Difference between revisions of "Zephyr"

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<center>
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[[Zephyr|Zephyr RTOS]] &nbsp; :: &nbsp; [[Device_tree|Device Tree]] &nbsp; :: &nbsp; [[Kconfig|Kconfig]] &nbsp; :: &nbsp; [[Cmake|cmake]]
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</center>
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<b>Overview</b>
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 +
This NN page a holding point for notes and links to external references regarding [https://github.com/zephyrproject-rtos/zephyr Zephyr RTOS], and [https://github.com/zephyrproject-rtos/ Zephyr RTOS Project].  Some key features of Zephyr RTOS include its designers' incorporation of [https://www.devicetree.org/ Device Tree Source] and Kconfig frameworks in this real time operating system.
 +
 +
As of 2023 April this page under reorganization, pulling multiple local pages into this page and removing older and defunct content - TMH
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 +
<i>
 +
For device tree and Kconfig see also:
 +
 +
*  https://www.kernel.org/doc/html/latest/kbuild/kconfig-language.html<br />
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*  https://github.com/ulfalizer/Kconfiglib Kconfig library parser and helper scripts project headed by Ulf Magnusson<br />
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</i>
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 +
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<!-- odne komentar -->
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<b>TODO:</b>
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 +
*  [ ] Find the meaning of the wrapping function this Zephyr header provides `$workspace/zephyr/include/zephyr/dt-bindings/dt-util.h`.
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*  [ ] Review the definition and implications of `__ASSERT` symbol defined in `$workspace/zephyr/include/zephyr/sys/__assert.h`.
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<!-- odne komentar -->
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 +
__TOC__
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== [[#top|^]] Zephyr Releases ==
 +
 +
Zephyr RTOS project itself, one of some one hundred twenty projects on Zephyr's Github page, has stable releases which become available once or twice a year.  The Zephyr RTOS repository itself is generally at a cutting edge of development.  It is `git tagged` or identified as a release candidate, until that point where the work has been finished to review all open issues and developments and create and tag a new stable release.
 +
 +
Zephyr RTOS release notes for various releases are found at https://docs.zephyrproject.org/latest/releases/.
 +
 +
Nordic Semi forks a recent, but not necessarily most recent stable release of Zephyr RTOS Project as part of its NCS Software Development Kit.
 +
 +
A local NN wiki page with some early Zephyr release notes is [[Zephyr_RTOS_releases|Zephyr RTOS releases]].  There may not be much to save from this article, but contributor Ted to review it.
 +
 +
As of summer 2024 Zephyr 3.7.0 LTS has been released:
 +
<ul>
 +
*  https://docs.zephyrproject.org/latest/releases/release-notes-3.7.html
 +
</ul>
 +
Board porting to move projects from older Zephyr releases to 3.7.0 LTS has a page, and also new `sysbuild` integration:
 +
<ul>
 +
*  https://docs.zephyrproject.org/latest/hardware/porting/board_porting.html#board-porting-guide
 +
 +
*  https://docs.zephyrproject.org/latest/build/sysbuild/index.html#sysbuild
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</ul>
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<!-- odne komentar -->
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== [[#top|^]] Zephyr Tutorials ==
 +
 +
Troubleshooting IoT Cellular Connections with Nordic nRF9160 . . .
 +
 +
*  https://blog.golioth.io/category/zephyr/page/2/
 +
 +
Mr. Green's Workshop tutorials on Zephyr and RPi Pico.  This article talks about three ways of classifying Zephyr based projects based on their top directory location relative to the instance of Zephyr SDK against which they build.
 +
 +
*  https://www.mrgreensworkshop.com/posts/2022-06-10-raspberry-pi-pico-zephyr-os-part-2
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 +
<!-- odne komentar -->
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== [[#top|^]] Zephyr Toolchain Installation ==
 +
 +
Complete notes for Zephyr toolchain installation and config are provided at Zephyr Project's [https://docs.zephyrproject.org/latest/develop/getting_started/index.html "Getting Started Guide"].
 +
 +
A final or near final step to setting up for Zephyr RTOS based projects, using Zephyr's `west` utility, involves performing a "west initialization" of the new workspace.  The two ways --manifest-url and -l (local) are detailed here:
 +
 +
*  https://docs.zephyrproject.org/latest/develop/west/built-in.html#west-init
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<!-- odne komentar -->
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== [[#top|^]] Zephyr Build Process ==
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 +
Zephyr based applications involve a build process which includes a kernel configuration or Kconfig parser, a Device Tree Source compiler `dtc`, and typically but not limited to a C or C++ compiler.
 +
 +
=== [[#top|^]] Build menuconfig target ===
 +
 +
How to build Zephyr app menuconfig target.
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 +
Zephyr's use of Kconfig has allowed for Zephyr project team to provide a 'menuconfig' build target as part of Zephyr's build configuration.  This means that Kconfig options can be studied and changed, and saved, via an ncurses based interactive tool.
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 +
Here is an example invocation to build the parts of a Zephyr based application sufficient to provide a menuconfig interactive session with that project.  The option past the double dashes spells out a relative path which fits the scenario in which the project's "primary" CMakeLists.txt file exists two directories below the project's `boards` directory:
 +
:
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  $ west build -b &lt;board/soc_or_mcu/core&gt; -t menuconfig -- -DBOARD_ROOT=../..
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 +
Older, to review and sort:
 +
 +
Possible to use Kconfig to pass along compiler options, such as `CONFIG_COMPILER_OPT`:
 +
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*  https://github.com/zephyrproject-rtos/zephyr/issues/46382
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<!-- odne komentar -->
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== ----- ----- -----  ----- ----- -----  ----- ----- ----- ==
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<!-- comentario -->
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== [[#top|^]] Zephyr Internals ==
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Zephyr RTOS run time starting point, for Zephyr v3.4.0 is function [https://github.com/zephyrproject-rtos/zephyr/blob/main/kernel/init.c#L529 function z_cstart()] in source file [https://github.com/zephyrproject-rtos/zephyr/blob/main/kernel/init.c init.c].
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 +
Zephyr util.h header file:
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<ul>
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${ZEPHYR_WORKSPACE}/zephyr/include/zephyr/sys/util.h:43:#define POINTER_TO_UINT(x) ((uintptr_t) (x))
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</ul>
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Error codes enumerated in errno.h:
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<ul>
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zephyr/lib/libc/minimal/include/errno.h
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</ul>
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<!-- odne komentar -->
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== [[#top|^]] Zephyr Macros ==
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<b>TODO 2024-07-31:</b> add links and notes on Zephyr RTOS util.h header file, a collection of macros and helper functions for common task.
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 +
Zephyr RTOS employs a lot of macros throughout its code base.  As a starting point, [https://docs.zephyrproject.org/3.6.0/kernel/services/other/atomic.html Zephyr's atomic services] use macros including [https://docs.zephyrproject.org/3.6.0/kernel/services/other/atomic.html#c.ATOMIC_BITMAP_SIZE ATOMIC_BITMAP_SIZE].  This macro is defined in file . . . atomic.h.
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<i>Excerpt from atomic.h:</i>
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<pre>
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85  * @brief This macro computes the number of atomic variables necessary to
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86  * represent a bitmap with @a num_bits.
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87  *
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88  * @param num_bits Number of bits.
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89  */
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90 #define ATOMIC_BITMAP_SIZE(num_bits) (ROUND_UP(num_bits, ATOMIC_BITS) / ATOMIC_BITS)
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</pre>
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<!-- odne komentar -->
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== [[#top|^]] Zephyr RTOS libc Choice And Constructs ==
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Zephyr RTOS project uses a particular version of C library `libc`.  Possibly entirely decoupled from this, Zephyr project uses in its toolchain a certain gcc cross compiler, which ships with some C header files containing important definitions.
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Zephyr based apps coded in C can have routines qualified with the macro implemented type `__printf_like`.  This macro has its definition in at least two files:
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<i>Figure x:  definition for __printf_like:</i><br />
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"./include/zephyr/toolchain/gcc.h"<br />
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"~/projects-sandbox/workspace-for-nexus/zephyr/lib/libc/minimal/source/stdout/fprintf.c"<br />
 +
 +
This may be worth exploring further.  See also NetBSD online manual page for C / Unix programming topic "attribute" at https://man.netbsd.org/attribute.3.  There is also a good forum post explanation on this macro at https://stackoverflow.com/questions/5825270/printflike-modifier.
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<!-- odne komentar -->
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== ----- ----- -----  ----- ----- -----  ----- ----- ----- ==
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<!-- odne komentar -->
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== [[#top|^]] Interrupts ==
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Zephyr RTOS provides some API and code facilities to support hardware interrupts, but each processor architecture has its own ways of implementing interrupts.  This local page section to cover issues and solutions to Zephyr application design with interrupts, and how to code for a given target processor.
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 +
First references:
 +
 +
*  https://docs.zephyrproject.org/3.3.0/kernel/services/interrupts.html#interrupts
 +
*  https://docs.zephyrproject.org/3.3.0/kernel/services/interrupts.html#c.k_is_in_isr
 +
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*  https://docs.zephyrproject.org/3.3.0/kernel/services/other/fatal.html#spurious-interrupts
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A Zephyr documentation on architecture porting, with references to lower level interrupt configuration code:
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 +
*  https://docs.zephyrproject.org/3.3.0/hardware/porting/arch.html#interrupt-and-exception-handling
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Zephyr's API macro for connecting a routine to a hardware interrupt is defined in `irq.h`:
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<pre>
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31 /**
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32  * @brief Initialize an interrupt handler.
 +
33  *
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34  * This routine initializes an interrupt handler for an IRQ. The IRQ must be
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35  * subsequently enabled before the interrupt handler begins servicing
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36  * interrupts.
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37  *
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38  * @warning
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39  * Although this routine is invoked at run-time, all of its arguments must be
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40  * computable by the compiler at build time.
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41  *
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42  * @param irq_p IRQ line number.
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43  * @param priority_p Interrupt priority.
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44  * @param isr_p Address of interrupt service routine.
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45  * @param isr_param_p Parameter passed to interrupt service routine.
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46  * @param flags_p Architecture-specific IRQ configuration flags..
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47  */
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48 #define IRQ_CONNECT(irq_p, priority_p, isr_p, isr_param_p, flags_p) \
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49        ARCH_IRQ_CONNECT(irq_p, priority_p, isr_p, isr_param_p, flags_p)
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</pre>
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<!-- odne komentar -->
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== [[#top|^]] Zephyr Threads ==
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An important executing element of a Zephyr based app is an application defined thread.  Zephyr based applications written in C will normally have at least one app side thread , which Zephyr will default to giving the name `main`.  This name reflects that application code begins executing from a function named `main()`, as is a long standing convention of C language.
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 +
Zephyr based applications can define threads of their own.  This is a multi-step action in the code, both at time of development and at run time.  Application defined threads are given numeric identifiers by Zephyr at run time;  only "main line" code of the app gets a named thread by default.  Developers however may optionally call a _Zephyr_API_ to give additional threads human meaningful names.
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=== [[#top|^]] Anatomy of a Zephyr thread ===
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To create a Zephyr thread in an app involves declarations of certain thread elements, a call to Zephyr's thread_create API function, and at minimum an entry point function for the given thread.  The following pieces:
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 +
<ul>
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*  thread data structure
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*  thread priority
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*  thread stack size
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*  call to Zephyr "create thread" API
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*  thread entry point function
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</ul>
 +
 +
In English language, creation of a Zephyr application thread in simple terms involves the steps:
 +
 +
(1)  create a thread's data structure of type `struct k_thread`<br />
 +
(2)  pound define given thread's priority<br />
 +
(3)  pound define given thread's static memory stack size in bytes<br />
 +
(4)  call Zephyr's thread creation API function with its required ten parameters<br />
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(5)  define an entry point function for the thread, which other application code most likely to call to start thread execution<br />
 +
 +
A bit of repetition:  Zephyr thread's data structure, priority and stack size are programmed in a declarative way.  Stack size and thread data are typically declared as follows, the first of these involves a function like macro:
 +
 +
<!-- ----------------------------------------------------------------------- -->
 +
<pre>
 +
K_THREAD_STACK_DEFINE(thread_led_stack_area, THREAD_LED_STACK_SIZE);
 +
 +
struct k_thread thread_led_data;
 +
</pre>
 +
<!-- ----------------------------------------------------------------------- -->
 +
 +
Interestingly, the stack area parameter first parameter to macro like function is defined in the above macro, and then referenced typically only one or two times, in the call to Zephyr's `k_thread_create()` API.
 +
 +
The call to `thread_create` <- REVIEW looks like this:
 +
 +
<!-- ----------------------------------------------------------------------- -->
 +
<pre>
 +
int initialize_thread_led(void)
 +
{
 +
    int rstatus = 0;
 +
 +
    k_tid_t task_led_tid = k_thread_create(&thread_led_data,
 +
                                          thread_led_stack_area,
 +
                                          K_THREAD_STACK_SIZEOF(thread_led_stack_area),
 +
                                          thread_led_entry_point,
 +
                                          NULL, NULL, NULL,
 +
                                          THREAD_LED_PRIORITY,
 +
                                          0,
 +
                                          K_MSEC(1000)); // K_NO_WAIT);
 +
 +
// REF https://docs.zephyrproject.org/2.6.0/reference/kernel/threads/index.html?highlight=k_thread_create#c.k_thread_name_set
 +
// int k_thread_name_set(k_tid_t thread, const char *str)
 +
 +
    rstatus = k_thread_name_set(task_led_tid, MODULE_ID__THREAD_LED);
 +
    if ( rstatus == 0 ) { } // avoid compiler warning about unused variable - TMH
 +
 +
    return (int)task_led_tid;
 +
}
 +
</pre>
 +
<!-- odne komentar -->
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=== [[#top|^]] Thread API references ===
 +
<ul>
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*  https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html?highlight=k_thread_define#c.K_THREAD_DEFINE
 +
 +
*  https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html?highlight=k_thread_create#c.k_thread_name_set
 +
</ul>
 +
<!-- comentario -->
 +
 +
== [[#top|^]] Zephyr Hardware Abstraction Layer ==
 +
Zephyr RTOS 3.4.0 project as of 2024 Q1 supports several MCU architectures plus an array of development boards.  Part of the framework for this support is a hardware abstraction layer, many of whose manifesting files are found along side Zephyr RTOS source tree in `$workspace/modules`.  The path `$workspace/modules/hal` contains vendor provided hardware libraries.
 +
 +
An example of a Zephyr HAL is `$workspace/modules/hal/nxp`.  This said, for Zephyr's supported in tree drivers there are sources which appear in Zephyr source tree itself to inform Zephyr about certain details of vendor HALs.
 +
 +
An example of source tree HAL references is the set of device tree source bindings files which live in `$workspace/zephyr/dts/bindings`.  As a case in point details for NXP's LPC family MCU pin and peripheral configurations are expressed in the file:
 +
 +
  $workspace/zephyr/dts/bindings/pinctrl/nxp,lpc-iocon-pinctrl.yaml
 +
 +
<!-- odne komentar -->
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== [[#top|^]] Zephyr Drivers ==
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 +
Zephyr RTOS has a notion of in-tree drivers and out-of-tree drivers.  The following local page section begin to cover these topics with a few references to specific peripheral drivers.
 +
 +
<ul><!-- CUSTOM INDENT - FOR SECTION IN-TREE DRIVERS - BEGIN -->
 +
<span id="anchor-nn-zephyr-in-tree-drivers"></span>
 +
=== [[#top|^]] In-tree drivers ===
 +
 +
Early in contributor Ted's learning and use of Zephyr RTOS, "in tree" drivers and "out of tree" drivers concepts seemed distinct and referent to code bases which were completely located within Zephyr's source tree, and the latter located outside of the Zephyr RTOS source tree, respectively.  This is not a correct view.  Rather, Zephyr's "in tree" drivers have code in the Zephyr source tree which nearly always calls third party MCU library code bases.
 +
 +
Out-out-tree drivers in contrast have their code bases entirely outside of Zephyr RTOS source tree.
 +
 +
Zephyr RTOS code provides standardized structures to support peripherals and devices.  These structures nearly always involve function pointers which ultimately point to a given target MCU or MCU family's driver library or Software Development Kit (SDK) code base.
 +
 +
Zephyr RTOS code base makes heavy use of function pointers and of macros.  These pointers and macros can make it a challenge to locate a function definiton during static code analysis.  The `ctags` utility does not always have a clear chain of symbols to follow to get to the ultimate definition of a function.
 +
 +
This NN article section on Zephyr in-tree drivers touches on this matter.  The subsection here on SPI NOR FLASH touches on this challenge, and looks at one way of following list files from build artifacts, to get closer to driver function definitions.
 +
 +
<ul><!-- CUSTOM INDENT - FOR DRIVER SUBSECTIONS - BEGIN -->
 +
==== [[#top|^]] ADC ====
 +
 +
Zephyr RTOS' in-tree Analog to Digital Converter (ADC) driver documentation point:
 +
 +
*  https://docs.zephyrproject.org/3.2.0/hardware/peripherals/adc.html#c.adc_channel_cfg.channel_id
 +
<!-- odne komentar -->
 +
==== [[#top|^]] UART ====
 +
 +
Zephyr in-tree UART driver supports polled, interrupt driven, and DMA based UART configurations.  First link to section of Zephyr 3.3.0 documentation on UART in-tree driver:
 +
<ul>
 +
*  https://docs.zephyrproject.org/3.3.0/hardware/peripherals/uart.html#asynchronous-api
 +
</ul>
 +
We are curious to see what support NXP offers in Zephyr 3.3.0 for UART DMA configuration.  Here are a couple of blog posts which may shed some light on needed code, and which code we need look for:
 +
<ul>
 +
*  https://medium.com/embedded-iot/how-to-write-uart-dma-driver-for-zephyr-9b5b7ed23c6c<br />
 +
 +
*  https://medium.com/embedded-iot/how-to-write-uart-dma-driver-for-zephyr-part-2-5a035328cc35<br />
 +
</ul>
 +
 +
On the topic of Zephyr UART via DMA support:
 +
<ul>
 +
*  https://devzone.nordicsemi.com/f/nordic-q-a/46426/dma-for-uart-with-zephyr-on-nrf9160
 +
A Nordic ncs sample application, likely good for any architecture independent Kconfig symbols:
 +
<ul><!-- L2 BEGIN -->
 +
*  https://github.com/nrfconnect/sdk-zephyr/tree/main/tests/drivers/uart/uart_async_api
 +
</ul><!-- L2 END -->
 +
Some mention of supported boards and dts overlay files in this testing yaml file:
 +
<ul><!-- L2 BEGIN -->
 +
*  https://github.com/nrfconnect/sdk-zephyr/blob/main/tests/drivers/uart/uart_async_api/testcase.yaml
 +
</ul><!-- L2 END -->
 +
</ul>
 +
<!-- odne komentar -->
 +
==== [[#top|^]] SPI ====
 +
 +
One specific SPI in-tree driver in Zephyr 3.4.0 is [https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/spi/spi_mcux_flexcomm.c spi_mcux_flexcomm.c].
 +
 +
The way Zephyr's spi.h and spi_mcux_flexcomm.c files connect to one another in terms of function calls is not clear, but there is a connection.
 +
 +
Using `ctags` to follow symbol and entity definitions seems to give an implied cyclic definition of `spi_transceive_dt()` API call in a Zephyr based app.  API spi_transceive_dt() maps to spi_transceive() per ctags results run in the Zephyr source tree.  But the function definition ultimately points to a reference to api->transceive.  Somehow, perhaps, the nature of the structures and pointers used to define a generalized interface which maps to a particular target MCU family makes it not possible for ctags to traverse the application side SPI transceive call to its ultimate definition.
 +
 +
The seeming circular definition point appears here in https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/drivers/spi.h#L761.
 +
 +
Zephyr's mandatory SPI driver API is called out in https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/drivers/spi.h#L647.
 +
 +
NXP / Freescale driver contribution spi_mcux_flexcomm.c provides this API here:
 +
 +
<ul>
 +
*  https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/spi/spi_mcux_flexcomm.c#L803
 +
</ul>
 +
 +
This excerpt is a snapshot of Zephyr 3.4.0, commit 356c8cbe63ae.  While it will change over time it is worth looking at here:
 +
 +
<pre>
 +
661
 +
662 static int transceive(const struct device *dev,
 +
663                      const struct spi_config *spi_cfg,
 +
664                      const struct spi_buf_set *tx_bufs,
 +
665                      const struct spi_buf_set *rx_bufs,
 +
666                      bool asynchronous,
 +
667                      spi_callback_t cb,
 +
668                      void *userdata)
 +
669 {
 +
670        struct spi_mcux_data *data = dev->data;
 +
671        int ret;
 +
672
 +
673        spi_context_lock(&data->ctx, asynchronous, cb, userdata, spi_cfg);
 +
674
 +
675        ret = spi_mcux_configure(dev, spi_cfg);
 +
676        if (ret) {
 +
677                goto out;
 +
678        }
 +
679
 +
680        spi_context_buffers_setup(&data->ctx, tx_bufs, rx_bufs, 1);
 +
681
 +
682        spi_context_cs_control(&data->ctx, true);
 +
683
 +
684        spi_mcux_transfer_next_packet(dev);
 +
685
 +
686        ret = spi_context_wait_for_completion(&data->ctx);
 +
687 out:
 +
688        spi_context_release(&data->ctx, ret);
 +
689
 +
690        return ret;
 +
691 }
 +
692
 +
693 static int spi_mcux_transceive(const struct device *dev,
 +
694                                const struct spi_config *spi_cfg,
 +
695                                const struct spi_buf_set *tx_bufs,
 +
696                                const struct spi_buf_set *rx_bufs)
 +
697 {
 +
698 #ifdef CONFIG_SPI_MCUX_FLEXCOMM_DMA
 +
699        return transceive_dma(dev, spi_cfg, tx_bufs, rx_bufs, false, NULL, NULL);
 +
700 #endif
 +
701        return transceive(dev, spi_cfg, tx_bufs, rx_bufs, false, NULL, NULL);
 +
702 }
 +
703
 +
</pre>
 +
 +
Also worth noting:
 +
 +
  ./mcux/mcux-sdk/drivers/spi/fsl_spi.c:1052:status_t SPI_MasterTransferNonBlocking(SPI_Type *base, spi_master_handle_t *handle, spi_transfer_t *xfer
 +
 +
An subtle interesting facet of Zephyr in-tree SPI driver is its code to deal with TX and RX buffers whose lengths differ.  See code at and around:
 +
 +
  https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/spi/spi_mcux_flexcomm.c#L106
 +
 +
- Recent code contributions to Zephyr SPI drivers -
 +
 +
A recent contributor issue to Zephyr in-tree driver code:
 +
 +
*  https://github.com/zephyrproject-rtos/zephyr/pull/66402/commits/01210979f941730690e273a2dc68570450011c43
 +
<!-- odne komentar -->
 +
==== [[#top|^]] SPI NOR FLASH ====
 +
 +
Zephyr provides a [https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/flash/spi_nor.c SPI NOR FLASH] driver API, which depending upon a developer's target MCU points to one or another third part SDK or driver code.  When working working with Zephyr 3.4.0 and a Macronix FLASH memory device, `ctags` isn't sufficient to locate the flash erase function definition.  A different search is needed.
 +
 +
Search steps:
 +
 +
Step (1) Begin with pattern match on project build artifact `build/cpu0/zephyr.lst`:
 +
 +
Excerpt:
 +
<pre>
 +
25552
 +
25553 10012f36 <flash_erase>:
 +
25554        rc = api->erase(dev, offset, size);
 +
25555 10012f36:      6883            ldr    r3, [r0, #8]
 +
25556 10012f38:      689b            ldr    r3, [r3, #8]
 +
25557 10012f3a:      4718            bx      r3
 +
25558 
 +
</pre>
 +
 +
There are other instances of routine name `flash_erase` but the clue in this excerpt is the data structure `api`.  A search in . . .
 +
 +
Step (2) Use ctags in app source file on API call `flash_erase`.  This goes to file `"$workspace/zephyr/include/zephyr/drivers/espi.h"`.  In this file find:
 +
 +
<pre>
 +
458 __subsystem struct espi_driver_api {
 +
459        espi_api_config config;
 +
460        espi_api_get_channel_status get_channel_status;
 +
461        espi_api_read_request read_request;
 +
462        espi_api_write_request write_request;
 +
463        espi_api_lpc_read_request read_lpc_request;
 +
464        espi_api_lpc_write_request write_lpc_request;
 +
465        espi_api_send_vwire send_vwire;
 +
466        espi_api_receive_vwire receive_vwire;
 +
467        espi_api_send_oob send_oob;
 +
468        espi_api_receive_oob receive_oob;
 +
469        espi_api_flash_read flash_read;
 +
470        espi_api_flash_write flash_write;
 +
471        espi_api_flash_erase flash_erase;
 +
472        espi_api_manage_callback manage_callback;
 +
473 };
 +
</pre>
 +
 +
Step (3) In zephyr.lst file use `ctags` to navigate to file `$workspace/zephyr/drivers/flash/soc_flash_nrf.c`.  Here find:
 +
 +
<pre>
 +
482 static int erase(uint32_t addr, uint32_t size)
 +
483 {
 +
484        struct flash_context context = { 
 +
485                .flash_addr = addr,
 +
486                .len = size,
 +
487 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
 +
488                .enable_time_limit = 0, /* disable time limit */
 +
489 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */
 +
490 #if defined(CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE)
 +
491                .flash_addr_next = addr
 +
492 #endif
 +
493        };
 +
494
 +
495        return  erase_op(&context);
 +
496 }
 +
</pre>
 +
 +
Given this it looks like step (2) did not directly help us reach the definition of `flash_erase()` API.  The apparent routine referenced on line 495 above has in same file the definition:
 +
 +
<pre>
 +
328 static int erase_op(void *context)
 +
329 {
 +
330        uint32_t pg_size = nrfx_nvmc_flash_page_size_get();
 +
331        struct flash_context *e_ctx = context;
 +
332
 +
333 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
 +
334        uint32_t i = 0U;
 +
335
 +
336        if (e_ctx->enable_time_limit) {
 +
337                nrf_flash_sync_get_timestamp_begin();
 +
338        }
 +
339 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */
 +
340
 +
341 #ifdef CONFIG_SOC_FLASH_NRF_UICR
 +
342        if (e_ctx->flash_addr == (off_t)NRF_UICR) {
 +
343                if (SUSPEND_POFWARN()) {
 +
344                        return -ECANCELED;
 +
345                }
 +
346
 +
347                (void)nrfx_nvmc_uicr_erase();
 +
348                RESUME_POFWARN();
 +
349                return FLASH_OP_DONE;
 +
350        }
 +
351 #endif
 +
352
 +
353        do {
 +
354                if (SUSPEND_POFWARN()) {
 +
355                        return -ECANCELED;
 +
356                }
 +
357
 +
358 #if defined(CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE)
 +
359                if (e_ctx->flash_addr == e_ctx->flash_addr_next) {
 +
360                        nrfx_nvmc_page_partial_erase_init(e_ctx->flash_addr,
 +
361                                CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE_MS);
 +
362                        e_ctx->flash_addr_next += pg_size;
 +
363                }
 +
364
 +
365                if (nrfx_nvmc_page_partial_erase_continue()) {
 +
366                        e_ctx->len -= pg_size;
 +
367                        e_ctx->flash_addr += pg_size;
 +
368                }
 +
369 #else
 +
370                (void)nrfx_nvmc_page_erase(e_ctx->flash_addr);
 +
371                e_ctx->len -= pg_size;
 +
372                e_ctx->flash_addr += pg_size;
 +
373 #endif /* CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE */
 +
374
 +
375                RESUME_POFWARN();
 +
376
 +
377 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
 +
378                i++;
 +
379
 +
380                if (e_ctx->enable_time_limit) {
 +
381                        if (nrf_flash_sync_check_time_limit(i)) {
 +
382                                break;
 +
383                        }
 +
384
 +
385                }
 +
386 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */
 +
387
 +
388        } while (e_ctx->len > 0);
 +
389
 +
390        return (e_ctx->len > 0) ? FLASH_OP_ONGOING : FLASH_OP_DONE;
 +
391 }
 +
</pre>
 +
 +
</ul><!-- CUSTOM INDENT - FOR DRIVER SUBSECTIONS - END -->
 +
<!-- odne komentar -->
 +
 +
=== [[#top|^]] Driver Code Factoring ===
 +
 +
In-tree Zephyr drivers exist as part of Zephyr's source code tree, in other words, the code repo that entails Zephyr RTOS itself.  Out-of-tree drivers written to cooperate with Zephyr exist outside of Zephyr's source code tree and are often their own independent code projects.  See however this local page's [[Zephyr#anchor-nn-zephyr-in-tree-drivers|In-tree drivers]] section for greater detail on driver code factoring in Zephyr RTOS.
 +
 +
Example Zephyr app and supporting code base which entails an out-of-tree driver factored along side app code:
 +
 +
*  https://github.com/nrfconnect/ncs-example-application
 +
</ul><!-- CUSTOM INDENT - FOR SECTION IN-TREE DRIVERS - END -->
 +
<!-- odne komentar -->
 +
 +
<ul><!-- CUSTOM INDENT - FOR SECTION OUT-OF-TREE DRIVERS - BEGIN -->
 +
<span id="anchor-nn-zephyr-out-of-tree-drivers"></span>
 +
=== [[#top|^]] Out-of-tree drivers ===
 +
 +
<i>Stub section for Zephyr out-of-tree drivers.</i>
 +
 +
</ul><!-- CUSTOM INDENT - FOR SECTION OUT-OF-TREE DRIVERS - END -->
 +
 +
== [[#top|^]] Zephyr Work Queues ==
 +
 +
Zephyr RTOS provides an RTOS feature called a work queue, which developers may define and use.  Zephyr also provides a system work queue.  The following Golioth blog post talks a bit about these:
 +
 +
*  https://blog.golioth.io/zephyr-threads-work-queues-message-queues-and-how-we-use-them/  Zephyr threads versus work queues
 +
 +
<!-- odne komentar -->
  
 
== [[#top|^]] Zephyr RTOS Logger and Backend Features ==
 
== [[#top|^]] Zephyr RTOS Logger and Backend Features ==
  
 +
Zephyr has five log levels ranging from [https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/logging/log_core.h#L19 LOG_LEVEL_NONE to LOG_LEVEL_DBG].  These are defined in [https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/logging/log_core.h log_core.h].
 +
 +
Printing of log messages and other strings can be deferred, and there is a mechanism in place in Zephyr RTOS project called `cbprintf packages` to help in this:
 +
 +
*  https://docs.zephyrproject.org/latest/services/formatted_output.html#cbprintf-packaging
 +
 +
It is also possible to reduce code size in a Zephyr app by avoiding libc library functions in the s*printf() family:
 +
 +
*  https://docs.zephyrproject.org/latest/services/formatted_output.html#formatted-output
 +
 +
 +
 +
<font color="red">Following links need updating to Zephyr 3.4.0:</font>
 +
 
*  https://docs.zephyrproject.org/2.6.0/reference/logging/index.html#logger-backend-interface
 
*  https://docs.zephyrproject.org/2.6.0/reference/logging/index.html#logger-backend-interface
 
*  https://docs.zephyrproject.org/2.6.0/reference/logging/index.html#default-frontend
 
*  https://docs.zephyrproject.org/2.6.0/reference/logging/index.html#default-frontend
Line 69: Line 651:
 
</pre>
 
</pre>
  
 +
But it looks like the routine is statically in-lined in Zephyr header file `log.h`:
  
−
<!-- comentario -->
+
<pre>
−
 
+
./include/logging/log.h:290:static inline char *log_strdup(const char *str)
−
== [[#top|^]] To Create And To Name Zephyr Threads ==
+
</pre>
−
 
 
−
*  https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html?highlight=k_thread_define#c.K_THREAD_DEFINE
 
−
 
 
−
*  https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html?highlight=k_thread_create#c.k_thread_name_set
 
  
 
<!-- comentario -->
 
<!-- comentario -->
Line 161: Line 740:
 
<!-- comentario -->
 
<!-- comentario -->
  
−
== [[#top|^]] struct thread_analyzer_info ==
+
=== [[#top|^]] struct thread_analyzer_info ===
  
 
<pre>
 
<pre>
 
ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr$ grep -nr 'struct thread_analyzer_info' ./*
 
ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr$ grep -nr 'struct thread_analyzer_info' ./*
−
./include/debug/thread_analyzer.h:23:struct thread_analyzer_info {
+
./include/debug/thre[[#top|^]] ad_analyzer.h:23:struct thread_analyzer_info {
 
./include/debug/thread_analyzer.h:44:typedef void (*thread_analyzer_cb)(struct thread_analyzer_info *info);
 
./include/debug/thread_analyzer.h:44:typedef void (*thread_analyzer_cb)(struct thread_analyzer_info *info);
 
</pre>
 
</pre>
Line 196: Line 775:
 
</pre>
 
</pre>
  
 +
<!-- comentario -->
 +
 +
== [[#top|^]] Zephyr Shell ==
 +
 +
This section started 2023-06-12.  Growth goal at this time is to learn how Zephyr shell supports multiple shell sessions, across one or many interfaces.
 +
 +
First reference noting here relates to develop needing to separate shell communications from Zephyr logging.  Not quite multi-session / multi-context shell support but somewhere in the ballpark:
 +
 +
*  https://github.com/zephyrproject-rtos/zephyr/issues/36057
 +
 +
This link asks salient questions to topic of multiple shell session support in Zephyr shell facility:
  
−
<!-- comentario -->
+
*  https://devzone.nordicsemi.com/f/nordic-q-a/92193/multiple-zephyr-shell-instances-over-uart
 +
*  https://devzone.nordicsemi.com/f/nordic-q-a/92325/use-shell-over-uart-and-uart-async-api-on-nrf52840
 +
<!-- odne komnentar -->
  
 
== ----- ----- -----  ----- ----- -----  ----- ----- ----- ==
 
== ----- ----- -----  ----- ----- -----  ----- ----- ----- ==
  
 
<!-- comentario -->
 
<!-- comentario -->
 +
 +
== [[#top|^]] Kernel Services ==
 +
 +
Zephyr stack sentinel
 +
 +
*  https://docs.zephyrproject.org/3.6.0/kconfig.html#CONFIG_STACK_SENTINEL
 +
 +
<!-- odne komentar -->
  
 
== Zephyr Memory Management ==
 
== Zephyr Memory Management ==
Line 212: Line 812:
 
== [[#top|^]] Zephyr Kernel Timing ==
 
== [[#top|^]] Zephyr Kernel Timing ==
  
−
Following link at Zephyr Project documentation pages has valuable info on various Zephyr timing and work queueing facilities:
+
System timing, timing of hardware and firmware running together is an important non-trivial feature of nearly all embedded systems.  In RTOS situations the operating system must expend some resources to keep track of a system timing mechanism with a time granularity of n microseconds.  The given system may use another unit of time but the concept remains the same.  Local article contributor Ted believes this applies for operating systems (and bare metal projects employing a timing mechanism) where there's a "system tick" or "systick" implemented.
 +
 
 +
Zephyr provides an API to permit firmware at runtime to obtain systick time granularity:
 +
 
 +
//  A Zephyr API to obtain MCU clock cycles per second:
 +
//    sys_clock_hw_cycles_per_sec()
 +
 
 +
 
 +
Program uptime or "running hours" may also be of import to a given project.  Following link at Zephyr Project documentation pages has valuable info on various Zephyr timing and work queueing facilities:
 
<ul>
 
<ul>
 
*  https://docs.zephyrproject.org/2.6.0/reference/kernel/timing/clocks.html?highlight=k_uptime
 
*  https://docs.zephyrproject.org/2.6.0/reference/kernel/timing/clocks.html?highlight=k_uptime
Line 230: Line 838:
 
*  https://github.com/zephyrproject-rtos/zephyr/issues/16238
 
*  https://github.com/zephyrproject-rtos/zephyr/issues/16238
  
 +
2023-12-06
 +
 +
In Zephyr a [https://docs.zephyrproject.org/latest/kernel/services/timing/clocks.html#c.k_timeout_t k_timeout_t] is a structure.
 +
 +
<!-- comentario -->
 +
 +
== [[#top|^]] Zephyr Application Code Relocation ==
 +
 +
*  https://docs.zephyrproject.org/3.1.0/kernel/code-relocation.html
  
 
<!-- comentario -->
 
<!-- comentario -->

Latest revision as of 17:43, 21 October 2024

Zephyr RTOS   ::   Device Tree   ::   Kconfig   ::   cmake


Overview

This NN page a holding point for notes and links to external references regarding Zephyr RTOS, and Zephyr RTOS Project. Some key features of Zephyr RTOS include its designers' incorporation of Device Tree Source and Kconfig frameworks in this real time operating system.

As of 2023 April this page under reorganization, pulling multiple local pages into this page and removing older and defunct content - TMH

For device tree and Kconfig see also:


TODO:

  • [ ] Find the meaning of the wrapping function this Zephyr header provides `$workspace/zephyr/include/zephyr/dt-bindings/dt-util.h`.
  • [ ] Review the definition and implications of `__ASSERT` symbol defined in `$workspace/zephyr/include/zephyr/sys/__assert.h`.


^ Zephyr Releases

Zephyr RTOS project itself, one of some one hundred twenty projects on Zephyr's Github page, has stable releases which become available once or twice a year. The Zephyr RTOS repository itself is generally at a cutting edge of development. It is `git tagged` or identified as a release candidate, until that point where the work has been finished to review all open issues and developments and create and tag a new stable release.

Zephyr RTOS release notes for various releases are found at https://docs.zephyrproject.org/latest/releases/.

Nordic Semi forks a recent, but not necessarily most recent stable release of Zephyr RTOS Project as part of its NCS Software Development Kit.

A local NN wiki page with some early Zephyr release notes is Zephyr RTOS releases. There may not be much to save from this article, but contributor Ted to review it.

As of summer 2024 Zephyr 3.7.0 LTS has been released:

Board porting to move projects from older Zephyr releases to 3.7.0 LTS has a page, and also new `sysbuild` integration:

^ Zephyr Tutorials

Troubleshooting IoT Cellular Connections with Nordic nRF9160 . . .

Mr. Green's Workshop tutorials on Zephyr and RPi Pico. This article talks about three ways of classifying Zephyr based projects based on their top directory location relative to the instance of Zephyr SDK against which they build.


^ Zephyr Toolchain Installation

Complete notes for Zephyr toolchain installation and config are provided at Zephyr Project's "Getting Started Guide".

A final or near final step to setting up for Zephyr RTOS based projects, using Zephyr's `west` utility, involves performing a "west initialization" of the new workspace. The two ways --manifest-url and -l (local) are detailed here:


^ Zephyr Build Process

Zephyr based applications involve a build process which includes a kernel configuration or Kconfig parser, a Device Tree Source compiler `dtc`, and typically but not limited to a C or C++ compiler.

^ Build menuconfig target

How to build Zephyr app menuconfig target.

Zephyr's use of Kconfig has allowed for Zephyr project team to provide a 'menuconfig' build target as part of Zephyr's build configuration. This means that Kconfig options can be studied and changed, and saved, via an ncurses based interactive tool.

Here is an example invocation to build the parts of a Zephyr based application sufficient to provide a menuconfig interactive session with that project. The option past the double dashes spells out a relative path which fits the scenario in which the project's "primary" CMakeLists.txt file exists two directories below the project's `boards` directory: 

 $ west build -b <board/soc_or_mcu/core> -t menuconfig -- -DBOARD_ROOT=../..

Older, to review and sort:

Possible to use Kconfig to pass along compiler options, such as `CONFIG_COMPILER_OPT`:


----- ----- ----- ----- ----- ----- ----- ----- -----

^ Zephyr Internals

Zephyr RTOS run time starting point, for Zephyr v3.4.0 is function function z_cstart() in source file init.c.

Zephyr util.h header file:

    ${ZEPHYR_WORKSPACE}/zephyr/include/zephyr/sys/util.h:43:#define POINTER_TO_UINT(x) ((uintptr_t) (x))

Error codes enumerated in errno.h:

    zephyr/lib/libc/minimal/include/errno.h


^ Zephyr Macros

TODO 2024-07-31: add links and notes on Zephyr RTOS util.h header file, a collection of macros and helper functions for common task.

Zephyr RTOS employs a lot of macros throughout its code base. As a starting point, Zephyr's atomic services use macros including ATOMIC_BITMAP_SIZE. This macro is defined in file . . . atomic.h.

Excerpt from atomic.h: 

 85  * @brief This macro computes the number of atomic variables necessary to
 86  * represent a bitmap with @a num_bits.
 87  *
 88  * @param num_bits Number of bits.
 89  */
 90 #define ATOMIC_BITMAP_SIZE(num_bits) (ROUND_UP(num_bits, ATOMIC_BITS) / ATOMIC_BITS)


^ Zephyr RTOS libc Choice And Constructs

Zephyr RTOS project uses a particular version of C library `libc`. Possibly entirely decoupled from this, Zephyr project uses in its toolchain a certain gcc cross compiler, which ships with some C header files containing important definitions.

Zephyr based apps coded in C can have routines qualified with the macro implemented type `__printf_like`. This macro has its definition in at least two files:

Figure x: definition for __printf_like:
"./include/zephyr/toolchain/gcc.h"
"~/projects-sandbox/workspace-for-nexus/zephyr/lib/libc/minimal/source/stdout/fprintf.c"

This may be worth exploring further. See also NetBSD online manual page for C / Unix programming topic "attribute" at https://man.netbsd.org/attribute.3. There is also a good forum post explanation on this macro at https://stackoverflow.com/questions/5825270/printflike-modifier.


----- ----- ----- ----- ----- ----- ----- ----- -----

^ Interrupts

Zephyr RTOS provides some API and code facilities to support hardware interrupts, but each processor architecture has its own ways of implementing interrupts. This local page section to cover issues and solutions to Zephyr application design with interrupts, and how to code for a given target processor.

First references:

A Zephyr documentation on architecture porting, with references to lower level interrupt configuration code:

Zephyr's API macro for connecting a routine to a hardware interrupt is defined in `irq.h`: 

 31 /**
 32  * @brief Initialize an interrupt handler.
 33  *
 34  * This routine initializes an interrupt handler for an IRQ. The IRQ must be
 35  * subsequently enabled before the interrupt handler begins servicing
 36  * interrupts.
 37  *
 38  * @warning
 39  * Although this routine is invoked at run-time, all of its arguments must be
 40  * computable by the compiler at build time.
 41  *
 42  * @param irq_p IRQ line number.
 43  * @param priority_p Interrupt priority.
 44  * @param isr_p Address of interrupt service routine.
 45  * @param isr_param_p Parameter passed to interrupt service routine.
 46  * @param flags_p Architecture-specific IRQ configuration flags..
 47  */
 48 #define IRQ_CONNECT(irq_p, priority_p, isr_p, isr_param_p, flags_p) \
 49         ARCH_IRQ_CONNECT(irq_p, priority_p, isr_p, isr_param_p, flags_p)


^ Zephyr Threads

An important executing element of a Zephyr based app is an application defined thread. Zephyr based applications written in C will normally have at least one app side thread , which Zephyr will default to giving the name `main`. This name reflects that application code begins executing from a function named `main()`, as is a long standing convention of C language.

Zephyr based applications can define threads of their own. This is a multi-step action in the code, both at time of development and at run time. Application defined threads are given numeric identifiers by Zephyr at run time; only "main line" code of the app gets a named thread by default. Developers however may optionally call a _Zephyr_API_ to give additional threads human meaningful names.

^ Anatomy of a Zephyr thread

To create a Zephyr thread in an app involves declarations of certain thread elements, a call to Zephyr's thread_create API function, and at minimum an entry point function for the given thread. The following pieces:

    • thread data structure
    • thread priority
    • thread stack size
    • call to Zephyr "create thread" API
    • thread entry point function

In English language, creation of a Zephyr application thread in simple terms involves the steps:

(1) create a thread's data structure of type `struct k_thread`
(2) pound define given thread's priority
(3) pound define given thread's static memory stack size in bytes
(4) call Zephyr's thread creation API function with its required ten parameters
(5) define an entry point function for the thread, which other application code most likely to call to start thread execution

A bit of repetition: Zephyr thread's data structure, priority and stack size are programmed in a declarative way. Stack size and thread data are typically declared as follows, the first of these involves a function like macro: 

K_THREAD_STACK_DEFINE(thread_led_stack_area, THREAD_LED_STACK_SIZE);

struct k_thread thread_led_data;

Interestingly, the stack area parameter first parameter to macro like function is defined in the above macro, and then referenced typically only one or two times, in the call to Zephyr's `k_thread_create()` API.

The call to `thread_create` <- REVIEW looks like this: 

int initialize_thread_led(void)
{
    int rstatus = 0;

    k_tid_t task_led_tid = k_thread_create(&thread_led_data,
                                           thread_led_stack_area,
                                           K_THREAD_STACK_SIZEOF(thread_led_stack_area),
                                           thread_led_entry_point,
                                           NULL, NULL, NULL,
                                           THREAD_LED_PRIORITY,
                                           0,
                                           K_MSEC(1000)); // K_NO_WAIT);

// REF https://docs.zephyrproject.org/2.6.0/reference/kernel/threads/index.html?highlight=k_thread_create#c.k_thread_name_set
// int k_thread_name_set(k_tid_t thread, const char *str)

    rstatus = k_thread_name_set(task_led_tid, MODULE_ID__THREAD_LED);
    if ( rstatus == 0 ) { } // avoid compiler warning about unused variable - TMH

    return (int)task_led_tid;
}

^ Thread API references

^ Zephyr Hardware Abstraction Layer

Zephyr RTOS 3.4.0 project as of 2024 Q1 supports several MCU architectures plus an array of development boards. Part of the framework for this support is a hardware abstraction layer, many of whose manifesting files are found along side Zephyr RTOS source tree in `$workspace/modules`. The path `$workspace/modules/hal` contains vendor provided hardware libraries.

An example of a Zephyr HAL is `$workspace/modules/hal/nxp`. This said, for Zephyr's supported in tree drivers there are sources which appear in Zephyr source tree itself to inform Zephyr about certain details of vendor HALs.

An example of source tree HAL references is the set of device tree source bindings files which live in `$workspace/zephyr/dts/bindings`. As a case in point details for NXP's LPC family MCU pin and peripheral configurations are expressed in the file: 

  $workspace/zephyr/dts/bindings/pinctrl/nxp,lpc-iocon-pinctrl.yaml


^ Zephyr Drivers

Zephyr RTOS has a notion of in-tree drivers and out-of-tree drivers. The following local page section begin to cover these topics with a few references to specific peripheral drivers.

    ^ In-tree drivers

    Early in contributor Ted's learning and use of Zephyr RTOS, "in tree" drivers and "out of tree" drivers concepts seemed distinct and referent to code bases which were completely located within Zephyr's source tree, and the latter located outside of the Zephyr RTOS source tree, respectively. This is not a correct view. Rather, Zephyr's "in tree" drivers have code in the Zephyr source tree which nearly always calls third party MCU library code bases.

    Out-out-tree drivers in contrast have their code bases entirely outside of Zephyr RTOS source tree.

    Zephyr RTOS code provides standardized structures to support peripherals and devices. These structures nearly always involve function pointers which ultimately point to a given target MCU or MCU family's driver library or Software Development Kit (SDK) code base.

    Zephyr RTOS code base makes heavy use of function pointers and of macros. These pointers and macros can make it a challenge to locate a function definiton during static code analysis. The `ctags` utility does not always have a clear chain of symbols to follow to get to the ultimate definition of a function.

    This NN article section on Zephyr in-tree drivers touches on this matter. The subsection here on SPI NOR FLASH touches on this challenge, and looks at one way of following list files from build artifacts, to get closer to driver function definitions.

      ^ ADC

      Zephyr RTOS' in-tree Analog to Digital Converter (ADC) driver documentation point:

      ^ UART

      Zephyr in-tree UART driver supports polled, interrupt driven, and DMA based UART configurations. First link to section of Zephyr 3.3.0 documentation on UART in-tree driver:

      We are curious to see what support NXP offers in Zephyr 3.3.0 for UART DMA configuration. Here are a couple of blog posts which may shed some light on needed code, and which code we need look for:

      On the topic of Zephyr UART via DMA support:

      ^ SPI

      One specific SPI in-tree driver in Zephyr 3.4.0 is spi_mcux_flexcomm.c.

      The way Zephyr's spi.h and spi_mcux_flexcomm.c files connect to one another in terms of function calls is not clear, but there is a connection.

      Using `ctags` to follow symbol and entity definitions seems to give an implied cyclic definition of `spi_transceive_dt()` API call in a Zephyr based app. API spi_transceive_dt() maps to spi_transceive() per ctags results run in the Zephyr source tree. But the function definition ultimately points to a reference to api->transceive. Somehow, perhaps, the nature of the structures and pointers used to define a generalized interface which maps to a particular target MCU family makes it not possible for ctags to traverse the application side SPI transceive call to its ultimate definition.

      The seeming circular definition point appears here in https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/drivers/spi.h#L761.

      Zephyr's mandatory SPI driver API is called out in https://github.com/zephyrproject-rtos/zephyr/blob/main/include/zephyr/drivers/spi.h#L647.

      NXP / Freescale driver contribution spi_mcux_flexcomm.c provides this API here:

      This excerpt is a snapshot of Zephyr 3.4.0, commit 356c8cbe63ae. While it will change over time it is worth looking at here: 

      661 
662 static int transceive(const struct device *dev,
663                       const struct spi_config *spi_cfg,
664                       const struct spi_buf_set *tx_bufs,
665                       const struct spi_buf_set *rx_bufs,
666                       bool asynchronous,
667                       spi_callback_t cb,
668                       void *userdata)
669 {
670         struct spi_mcux_data *data = dev->data;
671         int ret;
672 
673         spi_context_lock(&data->ctx, asynchronous, cb, userdata, spi_cfg);
674 
675         ret = spi_mcux_configure(dev, spi_cfg);
676         if (ret) {
677                 goto out;
678         }
679 
680         spi_context_buffers_setup(&data->ctx, tx_bufs, rx_bufs, 1);
681 
682         spi_context_cs_control(&data->ctx, true);
683 
684         spi_mcux_transfer_next_packet(dev);
685 
686         ret = spi_context_wait_for_completion(&data->ctx);
687 out:
688         spi_context_release(&data->ctx, ret);
689 
690         return ret;
691 }
692 
693 static int spi_mcux_transceive(const struct device *dev,
694                                const struct spi_config *spi_cfg,
695                                const struct spi_buf_set *tx_bufs,
696                                const struct spi_buf_set *rx_bufs)
697 {
698 #ifdef CONFIG_SPI_MCUX_FLEXCOMM_DMA
699         return transceive_dma(dev, spi_cfg, tx_bufs, rx_bufs, false, NULL, NULL);
700 #endif
701         return transceive(dev, spi_cfg, tx_bufs, rx_bufs, false, NULL, NULL);
702 }
703

      Also worth noting: 

       ./mcux/mcux-sdk/drivers/spi/fsl_spi.c:1052:status_t SPI_MasterTransferNonBlocking(SPI_Type *base, spi_master_handle_t *handle, spi_transfer_t *xfer

      An subtle interesting facet of Zephyr in-tree SPI driver is its code to deal with TX and RX buffers whose lengths differ. See code at and around: 

       https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/spi/spi_mcux_flexcomm.c#L106

      - Recent code contributions to Zephyr SPI drivers -

      A recent contributor issue to Zephyr in-tree driver code:

      ^ SPI NOR FLASH

      Zephyr provides a SPI NOR FLASH driver API, which depending upon a developer's target MCU points to one or another third part SDK or driver code. When working working with Zephyr 3.4.0 and a Macronix FLASH memory device, `ctags` isn't sufficient to locate the flash erase function definition. A different search is needed.

      Search steps:

      Step (1) Begin with pattern match on project build artifact `build/cpu0/zephyr.lst`:

      Excerpt: 

      25552 
25553 10012f36 <flash_erase>:
25554         rc = api->erase(dev, offset, size);
25555 10012f36:       6883            ldr     r3, [r0, #8]
25556 10012f38:       689b            ldr     r3, [r3, #8]
25557 10012f3a:       4718            bx      r3
25558

      There are other instances of routine name `flash_erase` but the clue in this excerpt is the data structure `api`. A search in . . .

      Step (2) Use ctags in app source file on API call `flash_erase`. This goes to file `"$workspace/zephyr/include/zephyr/drivers/espi.h"`. In this file find: 

       458 __subsystem struct espi_driver_api {
 459         espi_api_config config;
 460         espi_api_get_channel_status get_channel_status;
 461         espi_api_read_request read_request;
 462         espi_api_write_request write_request;
 463         espi_api_lpc_read_request read_lpc_request;
 464         espi_api_lpc_write_request write_lpc_request;
 465         espi_api_send_vwire send_vwire;
 466         espi_api_receive_vwire receive_vwire;
 467         espi_api_send_oob send_oob;
 468         espi_api_receive_oob receive_oob;
 469         espi_api_flash_read flash_read;
 470         espi_api_flash_write flash_write;
 471         espi_api_flash_erase flash_erase;
 472         espi_api_manage_callback manage_callback;
 473 };

      Step (3) In zephyr.lst file use `ctags` to navigate to file `$workspace/zephyr/drivers/flash/soc_flash_nrf.c`. Here find: 

      482 static int erase(uint32_t addr, uint32_t size)
483 {
484         struct flash_context context = {  
485                 .flash_addr = addr,
486                 .len = size,
487 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
488                 .enable_time_limit = 0, /* disable time limit */
489 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */ 
490 #if defined(CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE)
491                 .flash_addr_next = addr
492 #endif
493         };
494 
495         return  erase_op(&context);
496 }

      Given this it looks like step (2) did not directly help us reach the definition of `flash_erase()` API. The apparent routine referenced on line 495 above has in same file the definition: 

      328 static int erase_op(void *context)
329 {
330         uint32_t pg_size = nrfx_nvmc_flash_page_size_get();
331         struct flash_context *e_ctx = context;
332 
333 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
334         uint32_t i = 0U;
335 
336         if (e_ctx->enable_time_limit) {
337                 nrf_flash_sync_get_timestamp_begin();
338         }
339 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */
340 
341 #ifdef CONFIG_SOC_FLASH_NRF_UICR
342         if (e_ctx->flash_addr == (off_t)NRF_UICR) {
343                 if (SUSPEND_POFWARN()) {
344                         return -ECANCELED;
345                 }
346 
347                 (void)nrfx_nvmc_uicr_erase();
348                 RESUME_POFWARN();
349                 return FLASH_OP_DONE;
350         }
351 #endif
352 
353         do {
354                 if (SUSPEND_POFWARN()) {
355                         return -ECANCELED;
356                 }
357 
358 #if defined(CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE)
359                 if (e_ctx->flash_addr == e_ctx->flash_addr_next) {
360                         nrfx_nvmc_page_partial_erase_init(e_ctx->flash_addr,
361                                 CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE_MS);
362                         e_ctx->flash_addr_next += pg_size;
363                 }
364
365                 if (nrfx_nvmc_page_partial_erase_continue()) {
366                         e_ctx->len -= pg_size;
367                         e_ctx->flash_addr += pg_size;
368                 }
369 #else
370                 (void)nrfx_nvmc_page_erase(e_ctx->flash_addr);
371                 e_ctx->len -= pg_size;
372                 e_ctx->flash_addr += pg_size;
373 #endif /* CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE */
374 
375                 RESUME_POFWARN();
376 
377 #ifndef CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE
378                 i++;
379 
380                 if (e_ctx->enable_time_limit) {
381                         if (nrf_flash_sync_check_time_limit(i)) {
382                                 break;
383                         }
384 
385                 }
386 #endif /* !CONFIG_SOC_FLASH_NRF_RADIO_SYNC_NONE */
387 
388         } while (e_ctx->len > 0);
389 
390         return (e_ctx->len > 0) ? FLASH_OP_ONGOING : FLASH_OP_DONE;
391 }

    ^ Driver Code Factoring

    In-tree Zephyr drivers exist as part of Zephyr's source code tree, in other words, the code repo that entails Zephyr RTOS itself. Out-of-tree drivers written to cooperate with Zephyr exist outside of Zephyr's source code tree and are often their own independent code projects. See however this local page's In-tree drivers section for greater detail on driver code factoring in Zephyr RTOS.

    Example Zephyr app and supporting code base which entails an out-of-tree driver factored along side app code:

    ^ Out-of-tree drivers

    Stub section for Zephyr out-of-tree drivers.

^ Zephyr Work Queues

Zephyr RTOS provides an RTOS feature called a work queue, which developers may define and use. Zephyr also provides a system work queue. The following Golioth blog post talks a bit about these:


^ Zephyr RTOS Logger and Backend Features

Zephyr has five log levels ranging from LOG_LEVEL_NONE to LOG_LEVEL_DBG. These are defined in log_core.h.

Printing of log messages and other strings can be deferred, and there is a mechanism in place in Zephyr RTOS project called `cbprintf packages` to help in this:

It is also possible to reduce code size in a Zephyr app by avoiding libc library functions in the s*printf() family:


Following links need updating to Zephyr 3.4.0:

Zephyr's thread_analyzer when not configured to dump reports to printk() instead sends thread data to LOG_INF(). Excerpt from Zephyr file `./zephyr/subsys/debug/thread_analyzer.c`: 

 11 #include <kernel.h>
 12 #include <debug/thread_analyzer.h>
 13 #include <debug/stack.h>
 14 #include <kernel.h>
 15 #include <logging/log.h>
 16 #include <stdio.h>
 17 
 18 LOG_MODULE_REGISTER(thread_analyzer, CONFIG_THREAD_ANALYZER_LOG_LEVEL);
 19 
 20 #if IS_ENABLED(CONFIG_THREAD_ANALYZER_USE_PRINTK)
 21 #define THREAD_ANALYZER_PRINT(...) printk(__VA_ARGS__)
 22 #define THREAD_ANALYZER_FMT(str)   str "\n"
 23 #define THREAD_ANALYZER_VSTR(str)  (str)
 24 #else
 25 #define THREAD_ANALYZER_PRINT(...) LOG_INF(__VA_ARGS__)
 26 #define THREAD_ANALYZER_FMT(str)   str
 27 #define THREAD_ANALYZER_VSTR(str)  log_strdup(str)
 28 #endif

Zephyr macro `LOG_INF` is in turn defined: 

ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr$ grep -nr LOG_INF ./* | grep define

./include/logging/log.h:61:#define LOG_INF(...)   Z_LOG(LOG_LEVEL_INF, __VA_ARGS__)

Define of Z_LOG: 

ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr$ grep -nr 'Z_LOG[^_]' ./*

./include/logging/log_core.h:295:#define Z_LOG2(_level, _source, _dsource, ...) do { \
./include/logging/log_core.h:329:#define Z_LOG(_level, ...) \



$ grep -nr 'Z_LOG[^_]' ./*

$ vi ./include/logging/log_core.h

329 #define Z_LOG(_level, ...) \
330         Z_LOG2(_level, __log_current_const_data, __log_current_dynamic_data, __VA_ARGS__)


A Zephyr RTOS sample to check out:

`ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr/samples/subsys/logging/logger$`


- 2022-10-05 -

Zephyr v2.6.0 source file `log_core.h` may also define `log_strdup()`: 

./subsys/logging/log_core.c:1017:char *z_log_strdup(const char *str)

But it looks like the routine is statically in-lined in Zephyr header file `log.h`: 

./include/logging/log.h:290:static inline char *log_strdup(const char *str)


^ Zephyr thread_analyzer_cb And Related

Zephyr 2.6.0's thread_analyzer_cb() routine gathers and populates a structure with all pertinent, reported run-time thread statistics. This is however a static routine so we cannot call it directly. Nor does it return the summary thread resource use data to its direct calling routine. There is yet hope, and to understand a path forward here excerpted is the definition of this important thread reporting routine from file `./zephyr/subsys/debug/thread_analyzer.c`: 

 59 static void thread_analyze_cb(const struct k_thread *cthread, void *user_data)
 60 {
 61         struct k_thread *thread = (struct k_thread *)cthread;
 62 #ifdef CONFIG_THREAD_RUNTIME_STATS
 63         k_thread_runtime_stats_t rt_stats_all;
 64         k_thread_runtime_stats_t rt_stats_thread;
 65         int ret;
 66 #endif
 67         size_t size = thread->stack_info.size;
 68         thread_analyzer_cb cb = user_data;
 69         struct thread_analyzer_info info;
 70         char hexname[PTR_STR_MAXLEN + 1];
 71         const char *name;
 72         size_t unused;
 73         int err;
 74 
 75 
 76 
 77         name = k_thread_name_get((k_tid_t)thread);
 78         if (!name || name[0] == '\0') {
 79                 name = hexname;
 80                 snprintk(hexname, sizeof(hexname), "%p", (void *)thread);
 81         }
 82 
 83         err = k_thread_stack_space_get(thread, &unused);
 84         if (err) {
 85                 THREAD_ANALYZER_PRINT(
 86                         THREAD_ANALYZER_FMT(
 87                                 " %-20s: unable to get stack space (%d)"),
 88                         name, err);

 88                         name, err);
 89 
 90                 unused = 0;
 91         }
 92 
 93         info.name = name;
 94         info.stack_size = size;
 95         info.stack_used = size - unused;
 96 
 97 #ifdef CONFIG_THREAD_RUNTIME_STATS
 98         ret = 0;
 99 
100         if (k_thread_runtime_stats_get(thread, &rt_stats_thread) != 0) {
101                 ret++;
102         }
103 
104         if (k_thread_runtime_stats_all_get(&rt_stats_all) != 0) {
105                 ret++;
106         }
107         if (ret == 0) {
108                 info.utilization = (rt_stats_thread.execution_cycles * 100U) /
109                         rt_stats_all.execution_cycles;
110         }
111 #endif
112         cb(&info);
113 }

The routine which calls this is: 

115 void thread_analyzer_run(thread_analyzer_cb cb)
116 {
117         if (IS_ENABLED(CONFIG_THREAD_ANALYZER_RUN_UNLOCKED)) {
118                 k_thread_foreach_unlocked(thread_analyze_cb, cb);
119         } else {
120                 k_thread_foreach(thread_analyze_cb, cb);
121         }
122 }

We should be able to directly call thread_analyzer_run(thread_analyzer_cb cb). If yes, and if we can learn how &info is defined, we should be able to redirect thread_analyzer reports to an arbitrary UART . . .


^ struct thread_analyzer_info

ted@localhost:~/projects/zephyr-based/z4-sandbox-kionix-work/zephyr$ grep -nr 'struct thread_analyzer_info' ./*
./include/debug/thre[[#top|^]] ad_analyzer.h:23:struct thread_analyzer_info {
./include/debug/thread_analyzer.h:44:typedef void (*thread_analyzer_cb)(struct thread_analyzer_info *info);

Structure definition for &info passed to thread_analyzer_cb() function above: 

/** @defgroup thread_analyzer Thread analyzer
 *  @brief Module for analyzing threads
 *
 *  This module implements functions and the configuration that simplifies
 *  thread analysis.
 *  @{
 */

struct thread_analyzer_info {
        /** The name of the thread or stringified address of the thread handle
         * if name is not set.
         */
        const char *name;
        /** The total size of the stack*/
        size_t stack_size;
        /** Stack size in used */
        size_t stack_used;

#ifdef CONFIG_THREAD_RUNTIME_STATS
        unsigned int utilization;
#endif
};


^ Zephyr Shell

This section started 2023-06-12. Growth goal at this time is to learn how Zephyr shell supports multiple shell sessions, across one or many interfaces.

First reference noting here relates to develop needing to separate shell communications from Zephyr logging. Not quite multi-session / multi-context shell support but somewhere in the ballpark:

This link asks salient questions to topic of multiple shell session support in Zephyr shell facility:

----- ----- ----- ----- ----- ----- ----- ----- -----

^ Kernel Services

Zephyr stack sentinel


Zephyr Memory Management


^ Zephyr Kernel Timing

System timing, timing of hardware and firmware running together is an important non-trivial feature of nearly all embedded systems. In RTOS situations the operating system must expend some resources to keep track of a system timing mechanism with a time granularity of n microseconds. The given system may use another unit of time but the concept remains the same. Local article contributor Ted believes this applies for operating systems (and bare metal projects employing a timing mechanism) where there's a "system tick" or "systick" implemented.

Zephyr provides an API to permit firmware at runtime to obtain systick time granularity:

// A Zephyr API to obtain MCU clock cycles per second: // sys_clock_hw_cycles_per_sec()


Program uptime or "running hours" may also be of import to a given project. Following link at Zephyr Project documentation pages has valuable info on various Zephyr timing and work queueing facilities:

Related:

Important to follow up on this bug report relating to above mentioned Zephyr timing features:

2023-12-06

In Zephyr a k_timeout_t is a structure.


^ Zephyr Application Code Relocation


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