Armv8-M (except Cortex-M23) interrupt priority checking (#673)

* Armv8-M: Formatting changes

Signed-off-by: Devaraj Ranganna <>

* Armv8-M: Add support for interrupt priority check

FreeRTOS provides `FromISR` system calls which can be called directly
from interrupt service routines. It is crucial that the priority of
these ISRs is set to same or lower value (numerically higher) than that
of `configMAX_SYSCALL_INTERRUPT_PRIORITY`. For more information refer

Add a check to trigger an assert when an ISR with priority higher
(numerically lower) than `configMAX_SYSCALL_INTERRUPT_PRIORITY` calls
`FromISR` system calls if `configASSERT` macro is defined.

In addition, add a config option
`configQEMU_DISABLE_INTERRUPT_PRIO_BITS_CHECK` to disable interrupt
priority check while running on QEMU. Based on the discussion, The interrupt
priority bits in QEMU do not match the real hardware. Therefore the
assert that checks the number of implemented bits and __NVIC_PRIO_BITS
will always fail. The config option
 `configQEMU_DISABLE_INTERRUPT_PRIO_BITS_CHECK` should be defined in the
`FreeRTOSConfig.h` for QEMU targets.

Signed-off-by: Devaraj Ranganna <>

* Use SHPR2 for calculating interrupt priority bits

This removes the dependency on the secure software to mark the interrupt
as non-secure.

Signed-off-by: Gaurav Aggarwal <>


Signed-off-by: Devaraj Ranganna <>
Signed-off-by: Gaurav Aggarwal <>
Co-authored-by: Gaurav Aggarwal <>
Co-authored-by: Gaurav-Aggarwal-AWS <>
76 files changed
tree: 32bdc8b37abf9a4f11a1f9692dbaa469fb9244e0
  1. .github/
  2. include/
  3. portable/
  4. .git-blame-ignore-revs
  5. .gitattributes
  6. .gitmodules
  7. CMakeLists.txt
  8. event_groups.c
  9. GitHub-FreeRTOS-Kernel-Home.url
  10. History.txt
  12. list.c
  13. manifest.yml
  14. queue.c
  15. Quick_Start_Guide.url
  17. stream_buffer.c
  18. tasks.c
  19. timers.c

CMock Unit Tests codecov

Getting started

This repository contains FreeRTOS kernel source/header files and kernel ports only. This repository is referenced as a submodule in FreeRTOS/FreeRTOS repository, which contains pre-configured demo application projects under FreeRTOS/Demo directory.

The easiest way to use FreeRTOS is to start with one of the pre-configured demo application projects. That way you will have the correct FreeRTOS source files included, and the correct include paths configured. Once a demo application is building and executing you can remove the demo application files, and start to add in your own application source files. See the FreeRTOS Kernel Quick Start Guide for detailed instructions and other useful links.

Additionally, for FreeRTOS kernel feature information refer to the Developer Documentation, and API Reference.

Getting help

If you have any questions or need assistance troubleshooting your FreeRTOS project, we have an active community that can help on the FreeRTOS Community Support Forum.

To consume FreeRTOS-Kernel

Consume with CMake

If using CMake, it is recommended to use this repository using FetchContent. Add the following into your project‘s main or a subdirectory’s CMakeLists.txt:

  • Define the source and version/tag you want to use:
FetchContent_Declare( freertos_kernel
  GIT_TAG        main #Note: Best practice to use specific git-hash or tagged version
  • Add a freertos_config library (typically an INTERFACE library) The following assumes the directory structure:
    • include/FreeRTOSConfig.h
add_library(freertos_config INTERFACE)

target_include_directories(freertos_config SYSTEM

  • Configure the FreeRTOS-Kernel and make it available
    • this particular example supports a native and cross-compiled build option.
# Select the native compile PORT
# Select the cross-compile PORT


Consuming stand-alone - Cloning this repository

To clone using HTTPS:

git clone

Using SSH:

git clone

Repository structure

  • The root of this repository contains the three files that are common to every port - list.c, queue.c and tasks.c. The kernel is contained within these three files.

  • The ./portable directory contains the files that are specific to a particular microcontroller and/or compiler. See the readme file in the ./portable directory for more information.

  • The ./include directory contains the real time kernel header files.

Code Formatting

FreeRTOS files are formatted using the “uncrustify” tool. The configuration file used by uncrustify can be found in the .github/uncrustify.cfg file.

Line Endings

File checked into the FreeRTOS-Kernel repository use unix-style LF line endings for the best compatbility with git.

For optmial compatibility with Microsoft Windows tools, it is best to enable the git autocrlf feature. You can eanble this setting for the current repository using the following command:

git config core.autocrlf true

Git History Optimizations

Some commits in this repository perform large refactors which touch many lines and lead to unwanted behavior when using the git blame command. You can configure git to ignore the list of large refactor commits in this repository with the followig command:

git config blame.ignoreRevsFile .git-blame-ignore-revs


lexicon.txt contains words that are not traditionally found in an English dictionary. It is used by the spellchecker to verify the various jargon, variable names, and other odd words used in the FreeRTOS code base. If your pull request fails to pass the spelling and you believe this is a mistake, then add the word to lexicon.txt. Note that only the FreeRTOS Kernel source files are checked for proper spelling, the portable section is ignored.