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/**
\mainpage

\section Introduction

<a target="_blank" href="https://www.freertos.org/">FreeRTOS</a> is one of the market leading real-time operating systems
(RTOS) for embedded microcontrollers. It is professionally developed,
<a target="_blank" href="https://www.freertos.org/FreeRTOS-Coding-Standard-and-Style-Guide.html">strictly quality controlled</a>,
robust,
<a target="_blank" href="https://forums.freertos.org/">supported</a>
<a target="_blank" href="https://www.freertos.org/FreeRTOS_Support_Forum_Archive/freertos_support_forum_archive_index.html/">(archive)</a>,
free to <a target="_blank" href="https://www.freertos.org/a00114.html">use in commercial products</a> without a requirement to
expose proprietary source code, and has
<a target="_blank" href="https://www.freertos.org/differences-between-officially-supported-and-contributed-FreeRTOS-code.html">no IP infringement</a>
risk.

<a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/index.html"><b>CMSIS-RTOS v2</b></a> is a common API for real-time
operating systems (RTOS). It provides a standardized programming interface that is portable to many RTOS and enables software
components that can work across multiple RTOS systems. It supports the Armv8-M architecture, dynamic object creation, for
multi-core systems, and has a binary compatible interface across ABI compliant compilers.

Using this software pack, users can choose between a native FreeRTOS implementation or one that is adhering to the
CMSIS-RTOS2 API and using FreeRTOS under the hood. The CMSIS-RTOS2 API enables programmers to create portable application
code to be used with different RTOS kernels (for example
<a class="el" href="https://www2.keil.com/mdk5/cmsis/rtx/">Keil RTX5</a>).

This documentation shows you:
- how to \ref cre_freertos_proj "create a new microcontroller project" using FreeRTOS from scratch.
- Various \ref examples show you the usage of FreeRTOS in native and CMSIS-RTOS2 mode.
- the \ref tech_data of this implementation.
- \subpage rev_hist


License
-------

The CMSIS-FreeRTOS implementation is provided free of charge by Arm under the <a href="license.txt">FreeRTOS license</a>.


ARM::CMSIS-FreeRTOS Pack
------------------------

The <b>ARM::CMSIS-FreeRTOS</b> pack contains the following:

File/Directory             |Content
:--------------------------|:---------------------------------------------------------------------------------
\b CMSIS/Documentation     | This documentation.
\b CMSIS/RTOS2             | CMSIS-RTOS2 compliant implementation of FreeRTOS.
\b Config                  | FreeRTOS configuration header file.
\b License                 | FreeRTOS license agreement.
\b Source                  | FreeRTOS kernel source code.
\b ARM.CMSIS-FreeRTOS.pdsc | Package description file in CMSIS-Pack format.
*/

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/**
\page cre_freertos_proj Create a FreeRTOS project

You can basically choose between two option when creating a FreeRTOS project:
-# \ref native_freertos using the FreeRTOS API and kernel.
-# \ref cmsis_freertos using the CMSIS-RTOS2 API with an underlying FreeRTOS kernel.

\section native_freertos Create a native FreeRTOS project

The steps to create a microcontroller application using FreeRTOS are:
- Create a new project and select a microcontroller device.
- In the Manage Run-Time Environment window, select <b>\::Device:Startup</b>, <b>\::RTOS:CORE</b> and
  <b>\::RTOS:Config</b> in the \b FreeRTOS variant and an applicable <b>\::RTOS:Heap</b> scheme (for more
  information on the heap schemes, visit the FreeRTOS documentation):

  \image html manage_rte_freertos_native.png

  \n
- If the <b>Validation Output</b> requires other components to be present, try to use the \b Resolve button.
- Click \b OK. In the \b Project window, you will see the files that have been automatically added to you project, such as
  \b %FreeRTOSConfig.h, the source code files, as well as the system and startup files:

  \image html project_window_freertos_native.png

\subsection native_freertos_config Configure FreeRTOS

When you have created the native FreeRTOS project, you can configure the real-time operating system using the
\b FreeRTOSConfig.h file. Please refer to the
<a href="https://www.freertos.org/a00110.html" target="_blank">FreeRTOS documentation</a> for more information on the specific
settings.

\image html freertos_config_h_native.png


\subsection native_freertos_config_prio Interrupt priority configuration

FreeRTOS implements critical sections using the
<a href="https://developer.arm.com/documentation/dui0552/a/the-cortex-m3-processor/programmers-model/core-registers?lang=en" target="_blank">BASEPRI</a>
register (available in Armv7-M and Armv8-M architecture based devices) which masks only a subset of interrupts. This is
configured via the \c configMAX_SYSCALL_INTERRUPT_PRIORITY setting. Therefore, it is needed to properly configure this
setting. It is also needed to set appropriate interrupt priorities for interrupt service routines (ISR) that use RTOS
functions. This can especially impact drivers which typically use peripheral interrupts. Normally, these use the RTOS
directly or indirectly through registered callbacks.

Arm Cortex-M cores store interrupt priority values in the most significant bits of the interrupt priority registers which
can have a maximum of eight bits. Many implementations offer only three priority bits. These three bits are shifted up to be
bits five, six and seven respectively.
\c configMAX_SYSCALL_INTERRUPT_PRIORITY must not be 0 and can be xxx00000. This results in the following table:

| configMAX_SYSCALL_INTERRUPT_PRIORITY    | Upper three bits | Priority    |
|:---------------------------------------:|:----------------:|:-----------:|
| 32                                      | 001              | 1 (Highest) |
| 64                                      | 010              | 2           |
| 96                                      | 011              | 3           |
| 128                                     | 100              | 4           |
| 160                                     | 101              | 5           |
| 196                                     | 110              | 6           |
| 224                                     | 111              | 7 (Lowest)  |

\b Example

If you set \c configMAX_SYSCALL_INTERRUPT_PRIORITY to 32, then the priority of an interrupt service routine that uses RTOS
functions must then be higher or equal to 1. This ensures that this interrupt will be masked during critical a section.

A WiFi driver using the SPI interface registers a callback to SPI which is executed in an interrupt context. The callback
function in the WiFi driver uses RTOS functions. Therefore, the SPI interrupt priority must be set to a value equal or
higher to the FreeRTOS preempt priority, for example 1.

\note For a detailed description of how FreeRTOS is using Cortex-M code registers, refer to
<a href="https://www.freertos.org/RTOS-Cortex-M3-M4.html" target="_blank">Running the RTOS on a ARM Cortex-M Core</a>.


\subsection native_freertos_er Add Event Recorder Visibility
- To use the Event Recorder together with FreeRTOS, add the software component <b>\::Compiler:Event Recorder</b> to your project.
- Open \ref native_freertos_config "FreeRTOSConfig.h" and
  - verify the header file \b freertos_evr.h is included
  - add Event Recorder configuration definitions (see \ref cmsis_freertos_evr_config)
- Call <b>EvrFreeRTOSSetup()</b> in your application code (ideally in \c main()).
- If you are using simulation mode, add an initialization file with the following content:
  \code
  MAP 0xE0001000, 0xE0001007 READ WRITE
  signal void DWT_CYCCNT (void) {
  while (1) {
    rwatch(0xE0001004);
    _WWORD(0xE0001004, states);
    }
  }
  DWT_CYCCNT()
  \endcode
- Build the application code and download it to the debug hardware or run it in simulation.

Once the target application generates event information, it can be viewed in the µVision debugger using the <b>Event Recorder</b>.


\section cmsis_freertos Create a CMSIS-FreeRTOS project

The steps to create a microcontroller application using CMSIS-FreeRTOS are:
- Create a new project and select a microcontroller device.
- In the Manage Run-Time Environment window, select <b>\::Device:Startup</b>, <b>\::CMSIS::RTOS2 (API)\::FreeRTOS</b>,
  <b>\::RTOS:CORE</b> in the \b FreeRTOS variant, <b>\::RTOS:Config</b> in the \b CMSIS \b RTOS2 variant,
  <b>\::RTOS:Timers</b>, <b>\::RTOS:Event Groups</b>, and an applicable <b>\::RTOS:Heap</b>
  scheme (for more information on the heap schemes, visit the FreeRTOS documentation):

  \image html manage_rte_freertos_rtos2.png

  \n
- If the <b>Validation Output</b> requires other components to be present, try to use the \b Resolve button.
- Click \b OK. In the \b Project window, you will see the files that have been automatically added to you project, such as
  \b %FreeRTOSConfig.h, the source code files, as well as the system and startup files:

  \image html project_window_freertos_rtos2.png


\subsection cmsis_freertos_config Configure CMSIS-FreeRTOS

When you have created the CMSIS-FreeRTOS project, you can configure the real-time operating system using the
\b FreeRTOSConfig.h file. It can be opened using the Configuration Wizard view:

\image html freertos_config_h_cmsis_rtos.png

The following settings are available:

Name                           | \#define                             | Description                                                           |
-------------------------------|--------------------------------------|-----------------------------------------------------------------------|
Minimal stack size [words]     | configMINIMAL_STACK_SIZE             | Stack for idle task and default task stack in words.                  |
Total heap size [bytes]        | configTOTAL_HEAP_SIZE                | Heap memory size in bytes.                                            |
Kernel tick frequency [Hz]     | configTICK_RATE_HZ                   | Kernel tick rate in Hz.                                               |
Timer task stack depth [words] | configTIMER_TASK_STACK_DEPTH         | Stack for timer task in words.                                        |
Timer task priority            | configTIMER_TASK_PRIORITY            | Timer task priority.                                                  |
Timer queue length             | configTIMER_QUEUE_LENGTH             | Timer command queue length.                                           |
Preemption interrupt priority  | configMAX_SYSCALL_INTERRUPT_PRIORITY | Maximum priority of interrupts that are safe to call FreeRTOS API.    |
Use time slicing               | configUSE_TIME_SLICING               | Enable setting to use time slicing.                                   |
Idle should yield              | configIDLE_SHOULD_YIELD              | Control Yield behavior of the idle task.                              |
Check for stack overflow       | configCHECK_FOR_STACK_OVERFLOW       | Enable or disable stack overflow checking.                            |
Use idle hook                  | configUSE_IDLE_HOOK                  | Enable callback function call on each idle task iteration.            |
Use tick hook                  | configUSE_TICK_HOOK                  | Enable callback function call during each tick interrupt.             |
Use daemon task startup hook   | configUSE_DAEMON_TASK_STARTUP_HOOK   | Enable callback function call when timer service starts.              |
Use malloc failed hook         | configUSE_MALLOC_FAILED_HOOK         | Enable callback function call when out of dynamic memory.             |
Queue registry size            | configQUEUE_REGISTRY_SIZE            | Define maximum number of queue objects registered for debug purposes. |

\note Refer to \ref native_freertos_config_prio for more information on the usage of \c configMAX_SYSCALL_INTERRUPT_PRIORITY.

<b> Event Recorder Configuration </b>

The following settings are available (see \ref cmsis_freertos_evr_config for details):

Name                           | \#define                             | Description                                                                             |
-------------------------------|--------------------------------------|-----------------------------------------------------------------------------------------|
Initialize Event Recorder      | configEVR_INITIALIZE                 | Initialize Event Recorder before FreeRTOS kernel start.                                 |
Setup recording level filter   | configEVR_SETUP_LEVEL                | Enable configuration of FreeRTOS events recording level.                                |
Task functions                 | configEVR_LEVEL_TASKS                | Define event recording level bitmask for events generated from Tasks functions.         |
Queue functions                | configEVR_LEVEL_QUEUE                | Define event recording level bitmask for events generated from Queue functions.         |
Timer functions                | configEVR_LEVEL_TIMERS               | Define event recording level bitmask for events generated from Timer functions.         |
Event Groups functions         | configEVR_LEVEL_EVENTGROUPS          | Define event recording level bitmask for events generated from Event Groups functions.  |
Heap functions                 | configEVR_LEVEL_HEAP                 | Define event recording level bitmask for events generated from Heap functions.          |
Stream Buffer functions        | configEVR_LEVEL_STREAMBUFFER         | Define event recording level bitmask for events generated from Stream Buffer functions. |


\subsection cmsis_freertos_er Add Event Recorder Visibility
- To use the Event Recorder together with FreeRTOS, add the software component <b>\::Compiler:Event Recorder</b> to your project.
- Open \ref native_freertos_config "FreeRTOSConfig.h" and
  - verify the header file \b freertos_evr.h is included
  - modify Event Recorder configuration definitions (see \ref cmsis_freertos_evr_config) to change default configuration
- Call <b>osKernelInitialize()</b> in your application code (ideally in \c main()) to setup Event Recorder according to configuration settings.
- If you are using simulation mode, add an initialization file with the following content:
  \code
  MAP 0xE0001000, 0xE0001007 READ WRITE
  signal void DWT_CYCCNT (void) {
  while (1) {
    rwatch(0xE0001004);
    _WWORD(0xE0001004, states);
    }
  }
  DWT_CYCCNT()
  \endcode
- Build the application code and download it to the debug hardware or run it in simulation.

Once the target application generates event information, it can be viewed in the µVision debugger using the <b>Event Recorder.</b>


\section freertos_interfaces Create a mixed-interface project

Using CMSIS-RTOS2 API and native FreeRTOS API simultaneously is possible and some projects do require using the native FreeRTOS API and the CMSIS-RTOS2 API at the same time.
Such project should be \ref cmsis_freertos "created as CMSIS-FreeRTOS project".

Depending on the application requirements, FreeRTOS kernel can be started either by using FreeRTOS native API or by using CMSIS-RTOS2 API.

\subsection freertos_interface_rtos2 Start the kernel using CMSIS-RTOS2 API

\code
/*
  Application thread: Initialize and start the Application
*/
void app_main (void *argument) {

  while(1) {
    // Application code
    // ...
  }
}

/*
  Main function: Initialize and start the kernel
*/
int main (void) {
  SystemCoreClockUpdate();

  // Initialize CMSIS-RTOS2
  osKernelInitialize();

  // Create application main thread
  osThreadNew(app_main, NULL, NULL);

  // Start the kernel and execute the first thread
  osKernelStart();

  while(1);
}
\endcode

\b Restrictions

After the kernel is started using CMSIS-RTOS2 API, FreeRTOS native API can be used with the following restrictions:
- vTaskStartScheduler must not be called


\subsection freertos_interface_native Start the kernel using native API

\code
/*
  Application main thread: Initialize and start the application
*/
void app_main (void *argument) {

  while(1) {
    // Application code
    // ...
  }
}

/*
  Main function: Initialize and start the kernel
*/
int main (void) {
  SystemCoreClockUpdate();

  // Setup the Event Recorder (optionally)
  EvrFreeRTOSSetup(0);

  // Create application main thread
  xTaskCreate (app_main, "app_main", 64, NULL, tskIDLE_PRIORITY+1, NULL);

  // Start the kernel and execute the first thread
  vTaskStartScheduler();

  while(1);
}
\endcode

\b Restrictions

After the kernel is started using FreeRTOS native API, CMSIS-RTOS2 API can be used without restrictions.

\section cmsis_freertos_evr_config Configure Event Recorder

This section describes the configuration settings for the <a href="https://www.keil.com/pack/doc/compiler/EventRecorder/html/index.html" target="_blank">Event Recorder</a>
annotations. For more information refer to section \ref native_freertos_er "Add Event Recorder Visibility to native FreeRTOS project" or
\ref cmsis_freertos_er "Add Event Recorder Visibility to CMSIS-FreeRTOS project".

Use below definitions to configure Event Recorder initialization and recording level filter setup.

\code
#define configEVR_INITIALIZE
\endcode

Value  | Description                           |
-------|---------------------------------------|
0      | Disable Event Recorder initialization |
1      | Enable Event Recorder initialization  |

Definition configEVR_INITIALIZE enables Event Recorder initialization during execution of function \ref EvrFreeRTOSSetup. Default value is \token{1}.

\code
#define configEVR_SETUP_LEVEL
\endcode

Value  | Description                           |
-------|---------------------------------------|
0      | Disable recording level filter setup  |
1      | Enable recording level filter setup   |

Definition configEVR_SETUP_LEVEL enables setup of recording level filter for events generated by FreeRTOS. Recording level is configured during execution of function \ref EvrFreeRTOSSetup. Default value is \token{1}.

\code
#define configEVR_LEVEL_TASKS
#define configEVR_LEVEL_QUEUE
#define configEVR_LEVEL_TIMERS
#define configEVR_LEVEL_EVENTGROUPS
#define configEVR_LEVEL_HEAP
#define configEVR_LEVEL_STREAMBUFFER
\endcode

Value  | Description                                       |
-------|---------------------------------------------------|
0x00   | Disable event generation                          |
0x01   | Enable generation of error events                 |
0x05   | Enable generation of error and operational events |
0x0F   | Enable generation of all events                   |

Definitions configEVR_LEVEL_x set the recording level bitmask for events generated by each function group. They are taken into account only when recording level filter setup is enabled. Default value is \token{0x05}.


\section dbg_cmsisfreertos Debug a CMSIS-FreeRTOS project

\note The following only applies when used with <a href="https://www2.keil.com/mdk5" target="_blank">Arm Keil MDK</a>. If
you are using a different toolchain, please consult its user's manual.

Apart from the debug capabilities that \ref cmsis_freertos_evr_config "Event Recorder" offers, Keil MDK also supports thread
aware breakpoints, just like for the standard CMSIS-RTOS.

\b Code \b Example

\code
BS FuncN1, 1, "break = (CURR_TID == tid_phaseA) ? 1 : 0"
BS FuncN1, 1, "break = (CURR_TID == tid_phaseA || CURR_TID == tid_phaseD) ? 1 : 0"
BS \\Blinky\Blinky.c\FuncN1\179, 1, "break = (CURR_TID == tid_phaseA || CURR_TID == tid_phaseD) ? 1 : 0"
\endcode

\note
- For more information on conditional breakpoints in Keil MDK, consult the
  <a href="https://www.keil.com/support/man/docs/uv4/uv4_db_dbg_breakpnts.htm" target="_blank">user's manual</a>.
- Enabling <a href="https://www.keil.com/support/man/docs/uv4/uv4_ui_view.htm" target="_blank">Periodic Window Update</a> is
  required to capture register values for active running threads while executing. When turned off, only the current FreeRTOS
  thread can be unwound after execution has been stopped.

\b Caveats

- You cannot specify individual breakpoints on the same address. The following is not possible:
  \code
  BS ThCallee, 1, "break = (CURR_TID==tid_phaseA) ? 1 : 0"
  BS ThCallee, 1, "break = (CURR_TID==tid_phaseD) ? 1 : 0"
  \endcode
  Instead, use this:
  \code
  BS ThCallee, 1, "break= (CURR_TID==tid_phaseA || CURR_TID==tid_phaseD) ? 1 : 0"
  \endcode

- If you don't want to use
<a href="https://www.keil.com/support/man/docs/uv4/uv4_ui_view.htm" target="_blank">Periodic Window Update</a>, obtain the
thread and unwind information by adding a function that gets called from each thread of interest:
\code
_attribute_((noinline)) int FuncN1 (int n1) {
  ...
}
\endcode
Then, specify a thread aware breakpoint using an "invalid" thread ID:
\code
BS FuncN1, 1, "break = (CURR_TID == tid_phaseA + 1) ? 1 : 0"
\endcode
<tt>'tid_phaseA'</tt> would be valid, <tt>'tid_phaseA + 1'</tt> is not but will still capture the most recent registers and
store them to the actual thread context each time a thread aware breakpoint is checked.

- Function inlining typically causes thread aware breakpoints to fail. To avoid this, prepend the <tt>'noinline'</tt>
  attribute to the function that is used to stop when the current FreeRTOS thread id matches:
\code
_attribute_((noinline)) int FuncN1 (int n1) {
  ...
}
\endcode
This helps to make thread aware breakpoints far less dependent on the compiler optimization level.

- Thread aware breakpoints should be setup using a
<a href="https://www.keil.com/support/man/docs/uv4/uv4_db_scripting.htm" target="_blank">debug script</a>. Reason being
that thread aware breakpoints are of a 'hybrid' type, that is a combined address and condition expression that works best
when run from a debug script.
*/


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/**
\page examples Example projects

This pack contains two example projects:
 - \ref examples_native
 - \ref examples_cmsis

The first example shows how to use FreeRTOS standalone, whereas the second example shows how to use the CMSIS-RTOS2 API with
an underlying FreeRTOS.

The examples simulate a step-motor driver. Four phase variables are simulating the activation of the four output driver
stages. The state changes are shown in the Watch window variable \c g_phases. All four phases are displayed in the Logic
Analyzer:

\image html blinky_example_simu.png


\section examples_native Blinky example using FreeRTOS natively

This example shows how to use FreeRTOS natively in a µVision project. This makes your code portable and you can
choose to use a different RTOS kernel anytime during development (even only for evaluation purposes).

To open the example, go to Pack Installer, select \b ARM in the \b Devices tab, and click on \b Copy next to the
<b>Native FreeRTOS Blinky (uVision Simulator)</b> project on the \b Examples tab. Select the location on your hard drive
where you want to copy the project to and press OK. µVision opens.


\section examples_cmsis Blinky example using CMSIS-FreeRTOS

This example shows how to use the CMSIS-RTOS2 API with an underlying FreeRTOS. This makes your code portable and you can
choose to use a different RTOS kernel anytime during development (even only for evaluation purposes).

To open the example, go to Pack Installer, select \b ARM in the \b Devices tab, and click on \b Copy next to the
<b>CMSIS-RTOS2 FreeRTOS Blinky (uVision Simulator)</b> project on the \b Examples tab. Select the location on your hard drive
where you want to copy the project to and press OK. µVision opens.


\section examples_cmsis_a9 Blinky example using CMSIS-FreeRTOS running on Arm Cortex-A9

This example shows how to use the CMSIS-RTOS2 API with an underlying FreeRTOS running on an NXP i.MX6 equipped with an Arm
Cortex-A9 code. This example only works in <a href="https://www.keil.com/mdk5/ds-mdk">DS-MDK</a>, the Eclipse-based
development environment from Arm. For information on setting up the target connection, please refer to
<a href="https://www2.keil.com/mdk5/ds-mdk/imx6sxsabrereference">NXP i.MX 6SoloX SABRE Reference</a>.

\note you need to have the i.MX6 device family pack installed to see the example in the \b Examples tab of Pack Installer.

To open the example, open the Pack Installer perspective, select \b NXP in the \b Devices tab, and click on \b Copy next to
the <b>CMSIS-RTOS2 FreeRTOS Blinky CA9 (MCIMX6SX-SABRE)</b> project on the \b Examples tab.

\image html copy_a9_example.png

Confirm the default location in the Eclipse Workspace by pressing Copy.

\image html copy_a9_example_ws.png

Right-click on the project and select \b Build \b Project. Then, right-click on the project and select \b Debug \b As and
then \b Debug \b Configurations. The Debug Configurations dialog opens:

\image html dbg_conf.png

The project is already set up for running from the SDRAM of the i.MX6 SABRE board. Press \b Debug. DS-MDK will switch to the
debug perspective. After a successful connection to the target, press \b F8 to run the application. In the \b App \b Console
you will see the output of the phases:

\image html dbg_output.png
*/


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/**
\page tech_data Technical data and limitations

This lists the technical data of CMSIS-FreeRTOS.


\section td_limitations Limitations

The following list briefly describes the limitations and unsupported features of the CMSIS-RTOS2 wrapper for FreeRTOS:
- Static memory allocation will only work if \a all memory (from attributes structure) is provided statically. In order to
  allocate object memory statically, you need to:
  - provide the memory for control blocks and stack in the \c osThreadAttr_t structure for threads.
  - provide the memory for control blocks and message data in the \c osMessageQueueAttr_t structure for memory queues.
  - provide the memory for control blocks for other objects in the object's attributes structure.
- Each timer object requires additional 8 bytes of memory:
  - to allocate all memory statically, provide the memory for control block of size (sizeof(StaticTimer_t) + 8 bytes)
  - otherwise, additional 8 bytes of dynamic memory will be used
- \c osKernelSuspend and \c osKernelResume are not supported.
- \c osThreadDetach, \c osThreadJoin() and attribute \c osThreadJoinable are not supported (\c osThreadNew returns NULL when
  osThreadJoinable attribute is specified).
- \c osThreadGetStackSize is not implemented.
- Event flags are limited to 24 bits.
- \c osEventFlagsGetName is not implemented.
- \c osEventFlagsWait cannot be called from an ISR.
- Priority inherit protocol is used as default mutex behavior (\c osMutexNew creates priority inherit mutex object by default
  and ignores \c osMutexPrioInherit attribute when specified).
- Robust mutex objects are not supported (\c osMutexNew returns NULL when \c osMutexRobust attribute is specified).
- \c osMutexGetName is not implemented and always returns NULL.
- \c osSemaphoreGetName is not implemented and always returns NULL.
- \c osMessageQueueGetName is not implemented and always returns NULL.
- \c osMessageQueuePut and \c osMessageQueueGet always ignore message priority.

\section td_validation Validation suite results

CMSIS provides a
<a target="_blank" href="https://arm-software.github.io/CMSIS_5/RTOS2/html/rtosValidation.html">CMSIS-RTOS2 validation suite</a> that can
be used to test a real-time operating system for compliance to the standard. The test suite has been executed successfully on the
CMSIS-FreeRTOS implementation (<a href="cmsis_rtos2_validation.txt">see results</a>).

The following table explains the exceptions:

<table class="doxtable" summary="Validation Exceptions">
    <tr>
      <th>Test Case</th>
      <th>Result</th>
      <th>Reason</th>
      <th>Summary</th>
    </tr>
    <tr>
      <td>TC_osKernelGetState_2</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to call \c osKernelGetState after a \c osKernelSuspend call. osKernelSuspend is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osKernelLock_2</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to call \c osKernelLock after a \c osKernelSuspend call. \c osKernelSuspend is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osKernelUnlock_2</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to call \c osKernelUnlock after a \c osKernelSuspend call. \c osKernelSuspend is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osKernelSuspend_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osKernelSuspend which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osKernelResume_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osKernelResume which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadNew_3</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to create joinable thread using \c osThreadJoinable attribute. FreeRTOS does not support joinable threads.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadGetName_1</td>
      <td>failed</td>
      <td>deviation</td>
      <td>
        Test attempt to retrieve a name on an unnamed thread. An empty string is returned instead of NULL pointer.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadGetState_3</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to retrieve a state of a terminated joinable thread. FreeRTOS does not support joinable threads.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadDetach_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadDetach which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadDetach_2</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadDetach which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadJoin_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadJoin which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadJoin_2</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadJoin which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadJoin_3</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadJoin which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osThreadGetStackSize_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osThreadGetStackSize which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_ThreadReturn</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to terminate a thread by just returning from a thread. FreeRTOS threads may not return.
      </td>
    </tr>
    <tr>
      <td>TC_osEventFlagsSet_1</td>
      <td>failed</td>
      <td>deviation</td>
      <td>
        Test attempts to set event flags by calling \c osEventFlagsSet multiple times without leaving ISR handler.<br>
        To process ISR requests, FreeRTOS uses timer deamon which wakes-up after ISR execution.
      </td>
    </tr>
    <tr>
      <td>TC_osEventFlagsClear_1</td>
      <td>failed</td>
      <td>deviation</td>
      <td>
        Test attempts to clear event flags by calling \c osEventFlagsClear multiple times without leaving ISR handler.<br>
        To process ISR requests, FreeRTOS uses timer deamon which wakes-up after ISR execution.
      </td>
    </tr>
    <tr>
      <td>TC_osEventFlagsWait_1</td>
      <td>failed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to wait for flags from ISR with zero timeout (try-semantic). FreeRTOS does not support such operation.
      </td>
    </tr>
    <tr>
      <td>TC_osEventFlagsGetName_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osEventFlagsGetName which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osMutexNew_4</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to create a robust mutex. FreeRTOS implementation does not support robust mutexes.
      </td>
    </tr>
    <tr>
      <td>TC_osMutexGetName_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osMutexGetName which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_MutexRobust</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to validate robust mutex behavior. FreeRTOS implementation does not support robust mutexes.
      </td>
    </tr>
    <tr>
      <td>TC_MutexOwnership</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test attempts to release a mutex from a thread which is not the mutex owner.<br>
        FreeRTOS implementation does not verify ownership on mutex release.
      </td>
    </tr>
    <tr>
      <td>TC_osSemaphoreGetName_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osSemaphoreGetName which is not implemented.
      </td>
    </tr>
    <tr>
      <td>TC_osMessageQueueGetName_1</td>
      <td>not executed</td>
      <td>unsupported feature</td>
      <td>
        Test validates \c osMessageQueueGetName which is not implemented.
      </td>
    </tr>
</table>

\section td_troubleshooting Troubleshooting

Users looking for help shall check <a href="https://freertos.org/FAQHelp.html">subsection of the full FreeRTOS FAQ</a>.
It contains many useful information that also apply when using FreeRTOS in context of CMSIS-FreeRTOS.

Additionally, please take a look at the following:

<ol>
<li>
    <b>Interrupts are disabled when main is called or before the kernel is started</b>
    <br>
    Before the FreeRTOS kernel is started, threads (i.e. tasks) may be created together with other objects like
    mutexes, semaphores, message queues etc. When functions like xTaskCreate, xSemaphoreCreateMutex, xQueueCreate and
    others get called, they prevent interrupt handlers from calling FreeRTOS API functions in order to keep FreeRTOS kernel
    variables and state machine consistent
    (see also here <a href="https://freertos.org/FAQHelp.html">Interrupts are not executing</a>).
    <br>
    In cases when interrupts may be executed after object creation and before the FreeRTOS kernel is started they can be re-enabled:
    \code{.c}
        portENABLE_INTERRUPTS();
    \endcode
    Make sure that the interrupts you execute in such case do not call FreeRTOS API.
</li>
</ol>

*/


/*=======0=========1=========2=========3=========4=========5=========6=========7=========8=========9=========0=========1====*/
/**
\page functionOverview Function Overview


\section rtos_api2 CMSIS-RTOS2 API

Overview of all CMSIS-RTOS C API v2 functions that are implemented in CMSIS-FreeRTOS.

Kernel Information and Control
------------------------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__KernelCtrl.html">API reference</a> for details about Kernel Information and Control functions.
   - \b osKernelGetInfo: supported
   - \b osKernelGetState: supported
   - \b osKernelGetSysTimerCount: supported
   - \b osKernelGetSysTimerFreq: supported
   - \b osKernelInitialize: supported
   - \b osKernelLock: supported
   - \b osKernelUnlock: supported
   - \b osKernelRestoreLock: supported
   - \b osKernelResume: \token{not implemented}
   - \b osKernelStart: supported
   - \b osKernelSuspend: \token{not implemented}
   - \b osKernelGetTickCount: supported
   - \b osKernelGetTickFreq: supported


Thread Management
-----------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__ThreadMgmt.html">API reference</a> for details about Thread Management functions.
   - \b osThreadDetach: \token{not implemented}
   - \b osThreadEnumerate: supported
   - \b osThreadExit: supported
   - \b osThreadGetCount: supported
   - \b osThreadGetId: supported
   - \b osThreadGetName: supported
   - \b osThreadGetPriority: supported
   - \b osThreadGetStackSize: \token{not implemented}
   - \b osThreadGetStackSpace: supported
   - \b osThreadGetState: supported
   - \b osThreadJoin: \token{not implemented}
   - \b osThreadNew: supported
   - \b osThreadResume: supported
   - \b osThreadSetPriority: supported
   - \b osThreadSuspend: supported
   - \b osThreadTerminate: supported
   - \b osThreadYield: supported

Thread Flags
------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__ThreadFlagsMgmt.html">API reference</a> for details about Thread Flags functions.
   - \b osThreadFlagsSet: supported
   - \b osThreadFlagsClear: supported
   - \b osThreadFlagsGet: supported
   - \b osThreadFlagsWait: supported

Event Flags
-----------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__EventFlags.html">API reference</a> for details about Event Flags functions.
All event flags are limited to 24 bits.
   - \b osEventFlagsGetName: \token{not implemented}
   - \b osEventFlagsNew: supported
   - \b osEventFlagsDelete: supported
   - \b osEventFlagsSet: supported
   - \b osEventFlagsClear: supported
   - \b osEventFlagsGet: supported
   - \b osEventFlagsWait: cannot be called from an ISR.

Generic Wait Functions
----------------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__Wait.html">API reference</a> for details about Generic Wait functions.
   - \b osDelay: supported
   - \b osDelayUntil: supported

Timer Management
----------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__TimerMgmt.html">API reference</a> for details about Timer Management functions.</a>
   - \b osTimerDelete: supported
   - \b osTimerGetName: supported
   - \b osTimerIsRunning: supported
   - \b osTimerNew: supported
   - \b osTimerStart: supported
   - \b osTimerStop: supported

Mutex Management
----------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__MutexMgmt.html">API reference</a> for details about Mutex Management functions.\n
Priority inherit protocol is used as default mutex behavior (osMutexNew creates priority inherit mutex object by default
and ignores osMutexPrioInherit attribute when specified).\n
Robust mutex objects are not supported (osMutexNew returns NULL when osMutexRobust attribute is specified).\n
   - \b osMutexAcquire: supported
   - \b osMutexDelete: supported
   - \b osMutexGetName: \token{not implemented}
   - \b osMutexGetOwner: supported
   - \b osMutexNew: supported
   - \b osMutexRelease: supported

Semaphores
----------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__SemaphoreMgmt.html">API reference</a> for details about Semaphore functions.
   - \b osSemaphoreAcquire: supported
   - \b osSemaphoreDelete: supported
   - \b osSemaphoreGetCount: supported
   - \b osSemaphoreGetName: \token{not implemented}
   - \b osSemaphoreNew: supported
   - \b osSemaphoreRelease: supported

Memory Pool
-----------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__PoolMgmt.html">API reference</a> for details about Memory Pool functions.
   - \b osMemoryPoolAlloc: supported
   - \b osMemoryPoolDelete: supported
   - \b osMemoryPoolFree: supported
   - \b osMemoryPoolGetBlockSize: supported
   - \b osMemoryPoolGetCapacity: supported
   - \b osMemoryPoolGetCount: supported
   - \b osMemoryPoolGetName: supported
   - \b osMemoryPoolGetSpace: supported
   - \b osMemoryPoolNew: supported

Message Queue
-------------
See <a href="https://arm-software.github.io/CMSIS_5/RTOS2/html/group__CMSIS__RTOS__Message.html">API reference</a> for details about Message Queue functions.
   - \b osMessageQueueDelete: supported
   - \b osMessageQueueGet: ignores message priority.
   - \b osMessageQueueGetCapacity: supported
   - \b osMessageQueueGetCount: supported
   - \b osMessageQueueGetMsgSize: supported
   - \b osMessageQueueGetName: \token{not implemented}
   - \b osMessageQueueGetSpace: supported
   - \b osMessageQueueNew: supported
   - \b osMessageQueuePut: ignores message priority.
   - \b osMessageQueueReset: supported
*/

/* ======================================================================================================================== */
// Group creation for Reference
/**
\addtogroup freertos_specific CMSIS-FreeRTOS Specifics
\brief This section describes CMSIS-FreeRTOS specifics.
\details
CMSIS-FreeRTOS interfaces to the
<a href="https://www.keil.com/pack/doc/compiler/EventRecorder/html/index.html" target="_blank"><b>Event Recorder</b></a>
to provide event information which helps you to understand and analyze the operation. Refer to \ref freertos_evr for more
information.
*/