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Gaurav-Aggarwal-AWS 334de5d8ab
Enable ARMv7-M MPU ports to place FreeRTOS kernel code outside of flash (#46) 
Problem Description
-------------------
The current flash organization in ARMv7-M MPU ports looks as follows:

__FLASH_segment_start__ ------->+-----------+<----- __FLASH_segment_start__
                                |  Vector   |
                                |   Table   |
                                |     +     |
                                |   Kernel  |
                                |    Code   |
                                +-----------+<-----  __privileged_functions_end__
                                |           |
                                |           |
                                |           |
                                |   Other   |
                                |   Code    |
                                |           |
                                |           |
                                |           |
   __FLASH_segment_end__ ------>+-----------+

The FreeRTOS kernel sets up the following MPU regions:

* Unprivileged Code - __FLASH_segment_start__ to __FLASH_segment_end__.
* Privileged Code - __FLASH_segment_start__ to __privileged_functions_end__.

The above setup assumes that the FreeRTOS kernel code
(i.e. privileged_functions) is placed at the beginning of the flash and,
therefore, uses __FLASH_segment_start__ as the starting location of the
privileged code. This prevents a user from placing the FreeRTOS kernel
code outside of flash (say to an external RAM) and still have vector
table at the beginning of flash (which is many times a hardware
requirement).

Solution
--------
This commit addresses the above limitation by using a new variable
__privileged_functions_start__ as the starting location of the
privileged code. This enables users to place the FreeRTOS kernel code
wherever they choose.

The FreeRTOS kernel now sets up the following MPU regions:

* Unprivileged Code - __FLASH_segment_start__ to __FLASH_segment_end__.
* Privileged Code - __privileged_functions_start__ to __privileged_functions_end__.

As a result, a user can now place the kernel code to an external RAM. A
possible organization is:

                                 Flash              External RAM
                              +------------+        +-----------+<------ __privileged_functions_start__
                              |   Vector   |        |           |
                              |   Table    |        |           |
                              |            |        |           |
__FLASH_segment_start__ ----->+------------+        |   Kernel  |
                              |            |        |    Code   |
                              |            |        |           |
                              |            |        |           |
                              |            |        |           |
                              |   Other    |        |           |
                              |    Code    |        +-----------+<------ __privileged_functions_end__
                              |            |
                              |            |
                              |            |
  __FLASH_segment_end__ ----->+------------+

Note that the above configuration places the vector table in an unmapped
region. This is okay because we enable the background region, and so the
vector table will still be accessible to the privileged code and not
accessible to the unprivileged code (vector table is only needed by the
privileged code).

Backward Compatibility
----------------------
The FreeRTOS kernel code now uses a new variable, namely
__privileged_functions_start__, which needs to be exported from linker
script to indicate the starting location of the privileged code. All of
our existing demos already export this variable and therefore, they will
continue to work.

If a user has created a project which does not export this variable,
they will get a linker error for unresolved symbol
__privileged_functions_start__. They need to export a variable
__privileged_functions_start__ with the value equal to
__FLASH_segment_start__.

Issue
-----
https://sourceforge.net/p/freertos/feature-requests/56/

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
2020-04-06 15:51:40 -07:00
.github Create pull_request_template.md 2020-03-17 13:11:11 -07:00
include Improve documentation for the ulTaskNotifyValueClear() and xTaskCatchUpTicks() API functions. 2020-03-15 20:24:18 -07:00
portable Enable ARMv7-M MPU ports to place FreeRTOS kernel code outside of flash (#46) 2020-04-06 15:51:40 -07:00
CONTRIBUTING.md Added CONTRIBUTING (#18) 2020-02-25 16:22:57 -08:00
croutine.c Updates vCoRoutineSchedule() so it returns without doing anything if if the co-routine internal data structures have not been initialised. The internal data structures are initialised when the first co-routine is created. 2020-02-26 10:45:32 -08:00
event_groups.c version bump to v10.3.1 (#16) 2020-02-18 22:03:54 -08:00
GitHub-FreeRTOS-Kernel-Home.url Adding url to direct users to FreeRTOS-Kernel github page. (#32) 2020-03-17 19:30:19 -07:00
History.txt version bump to v10.3.1 (#16) 2020-02-18 22:03:54 -08:00
LICENSE.md Bring license in sync with FreeRTOS/FreeRTOS. (#20) 2020-02-27 14:33:46 -08:00
list.c version bump to v10.3.1 (#16) 2020-02-18 22:03:54 -08:00
queue.c Small typo on L1287 (#14) 2020-02-19 14:05:48 -08:00
Quick_Start_Guide.url Add quick start guide. 2013-04-30 19:37:00 +00:00
README.md Replacing readme.txt with README.md. (#11) 2020-02-16 13:18:58 -08:00
SECURITY.md Create SECURITY.md 2020-03-17 13:08:50 -07:00
stream_buffer.c version bump to v10.3.1 (#16) 2020-02-18 22:03:54 -08:00
tasks.c pxTCB is no longer needed in this local function. 2020-03-24 11:51:17 -07:00
timers.c version bump to v10.3.1 (#16) 2020-02-18 22:03:54 -08:00

README.md

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.

Cloning this repository

To clone using HTTPS:

git clone https://github.com/FreeRTOS/FreeRTOS-Kernel.git

Using SSH:

git clone git@github.com:FreeRTOS/FreeRTOS-Kernel.git

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. croutine.c implements the optional co-routine functionality - which is normally only used on very memory limited systems.

  • 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.