X-LINUX-RT expansion package

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

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This article describes the content of X-LINUX-RT expansion package release version v6.0.0, which can be applied on top of STM32 MPU ecosystem release note - v6.0.0.

1. Article purpose

Purpose of this article is to:

• introduce the X-LINUX-RT expansion package,
• define the hardware & software deliverables to use the X-LINUX-RT package,
• describe all steps to integrate the X-LINUX-RT package and associated expected results,
• give some use case examples enabled by the X-LINUX-RT package.

2. X-LINUX-RT expansion package description

2.1. Overview

X-LINUX-RT is an STM32 MPU OpenSTLinux expansion package that targets the real-time (RT) feature in the Linux^® kernel.
An RT system is a system that responds to a request in a time lapse and not as fast as possible. It targets​:

• Determinism​
• LATENCY but not SPEED

For a better understanding about real-time Linux, refer to the Linux RT foundation website.

The X-LINUX-RT expansion package is delivered as a new meta layer. The following chapters show how to build it with the OpenSTLinux Distribution Package.

2.2. Main software modifications

2.2.1. Linux kernel configuration

The Linux kernel configuration must be modified to enable:

• CONFIG_PREEMPT_RT: RT feature in kernel
• CONFIG_HIGH_RES_TIMERS: high resolution timer support

2.2.2. OP-TEE OS configuration

2.2.2.1. OP-TEE OS Profile

It is recommended to set OP-TEE OS in a system_services profile in order to optimize the system latency (Refer to STM32MPU_OP-TEE_profiles for more details about OP-TEE profiles).
It is configured by default in context of OpenSTLinux Distribution Package, and has to be considered in case of OpenSTLinux Developer Package as described in below chapters.

2.2.2.2. OP-TEE OS board device trees

Power management is not "compliant" with a real-time context as it changes the system behavior. Because there is no more frequency scaling, and to ensure an optimal lifetime for the microprocessor, the frequency is fixed following the recommended industrial profile.

• 900 MHz for STM32MP13x lines 
• 650 MHz for STM32MP15x lines 
• 1.2 GHz for STM32MP25x lines 

2.3. Main restrictions

X-LINUX-RT is only available as a Distribution Package. There are no X-LINUX-RT Started package nor X-LINUX-RT Developer Package.

You can nevertheless learn how to install the X-LINUX-RT feature in your OpenSTLinux Developer Package.

2.4. Versioning

The latest version of the X-LINUX-RT expansion package is named openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06 and must be used with components delivered for ecosystem release v6.0.0 .

2.5. Associated licenses

This software package is licensed under a SOFTWARE LICENSE AGREEMENT FOR ST MATERIALS (SLA). Customers should only use this package in compliance with the software license agreement (SLA), STM32CubeMP15 licenses, and STM32CubeMP2 licenses.

3. Prerequisites

3.1. Hardware prerequisites

• Below the list of supported STM32 MPU boards. Click on the associated links to jump to articles describing how to set up the boards: they explain how to assemble the boards, set the right power jumper configuration, connect the display to the board and connect the board to your development environment.

Boards should be assembled as defined in those articles.

STM32MP135x-DK - hardware description

STM32MP157x-DKx - hardware description

STM32MP157x-EV1 - hardware description

STM32MP257x-EV1 - hardware description

3.2. Software prerequisites

Be familiar with:

• OpenSTLinux Distribution Package. Refer to the STM32MPU Distribution Package article for more information.
• OpenSTLinux Developer Package. Refer to the STM32MPU Developer Package article for more information.

• Get the OpenSTLinux ecosystem release v6.0.0 (steps to follow described in chapters below).

4. Hardware Setup

Boards should be assembled as defined in #Hardware prerequisites.

5. Software setup

5.1. How to get software

X-LINUX-RT expansion package is delivered in a git repository on Github: https://github.com/STMicroelectronics/meta-st-x-linux-rt.git (Scarthgap branch for compatibility with this ecosystem release v6.0.0 )

It can be integrated using OpenSTLinux Distribution Package to build new OpenSTLinux images.

5.1.1. How to install the Distribution Package

5.1.1.1. Install the OpenSTLinux Distribution Package

Install the OpenSTLinux Distribution Package v6.0.0.

5.1.1.2. Download the X-LINUX-RT meta layer

• Clone the meta-st-x-linux-rt git repositories

pushd <Distribution Package installation directory>/layers/meta-st
git clone -b mickledore https://github.com/STMicroelectronics/meta-st-x-linux-rt.git -b openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06
popd

• Source the build environment with the correct board and layer

For STM32MP13x lines :

DISTRO=openstlinux-weston MACHINE=stm32mp13-rt source layers/meta-st/scripts/envsetup.sh

For STM32MP15x lines :

DISTRO=openstlinux-weston MACHINE=stm32mp1-rt source layers/meta-st/scripts/envsetup.sh

For STM32MP2 series (for ecosystem release v6.0.0 ):

DISTRO=openstlinux-weston MACHINE=stm32mp2-rt source layers/meta-st/scripts/envsetup.sh

• Build the image

bitbake st-image-weston

Information

Note that building the image might take a long time depending on the host computer performance.

5.1.2. How to populate the flash memory with the image

You can refer to Flashing the built image to program your board with X-LINUX-RT binaries.

5.1.3. How to run X-LINUX-RT package software

To run X-LINUX-RT package software, just boot the image, loaded on the board, as explained in previous chapters.

5.2. How to check that RT feature is enabled

To check that the RT feature is enabled and functional, the following command can be executed when the board is running, to check the kernel version:

uname -s -r -v

Without the RT feature	Linux 6.6.48 #1 SMP PREEMPT Fri Mar 15 14:04:26 UTC 2024
With the RT feature	Linux 6.6.48-rt27 #1 SMP PREEMPT_RT Fri Mar 15 18:27:50 UTC 2024

6. How to run Cyclictest

6.1. Use cases execution and expected results

Cyclictest accurately and repeatedly measures the difference between the time at which a thread is intended to wake up and the time at which it actually wakes up.
For a better understanding of cyclictest, refer to the cyclictest webpage in the Linux RT foundation website.

For example, the following command can be used for one hour test: (--quiet option can be added to improve measurement)

cyclictest --mlockall --smp -p 99 -i 100 -d 0 -A 0 -D 1h

Without the RT feature	... T: 0 ( 1667) P:99 I:200 C: 1000 Min: 21 Act: 40 Avg: 33 Max: 103 T: 1 ( 1668) P:99 I:200 C: 882 Min: 21 Act: 58 Avg: 42 Max: 187 ...
With the RT feature	... T: 0 ( 2131) P:99 I:100 C:36000000 Min: 7 Act: 10 Avg: 10 Max: 52 T: 1 ( 2132) P:99 I:100 C:36000000 Min: 7 Act: 11 Avg: 10 Max: 94 ...

Note: OPTEE HSI cyclic calibration was deactivated for this test

6.2. Use case restrictions

None

7. How to go further

7.1. How to improve system latency in RT mode

To improve latency, a new DISTRO, named openstlinux-rt, is provided with the X-LINUX RT package.
This DISTRO is based on following characteristics:

• it uses SysVinit instead of SystemD,
• there is no Weston,
• there is no OPTEE HSI cyclic calibration,
• there is no Netdata services.

7.1.1. Build openstlinux-rt

If not done yet, set up the X-LINUX-RT Distribution Package as described #How to install the Distribution Package chapter.

To select the openstlinux-rt DISTRO, run following command:

DISTRO=openstlinux-rt MACHINE=<your machine> source layers/meta-st/scripts/envsetup.sh

Build the image

bitbake st-image-core

7.1.2. Flash openstlinux-rt

Then flash it, as explained here.

7.1.3. Performances measurement

RT performances should be improved. To check run cyclictest  :

cyclictest --mlockall --smp -p 99 -i 100 -d 0 -A 0 -D 1h
...
T: 0 ( 2131) P:99 I:100 C:36000000 Min:      7 Act:   10 Avg:   10 Max:      46
T: 1 ( 2132) P:99 I:100 C:36000000 Min:      7 Act:   11 Avg:   10 Max:      44
...

7.2. How to install X-LINUX-RT in the OpenSTLinux Developer Package

In order to build Linux RT, apply patches and device tree files provided in X-LINUX-RT meta layer on top of the OpenSTLinux BSP components.

7.2.1. Install the OpenSTLinux SDK

The OpenSTLinux SDK contains all the basis needed for the X-LINUX-RT expansion package.

It must be downloaded and installed (refer to the STM32MPU_Developer_Package#Installing_the_SDK chapter).

Once the installation is done, a directory is present, containing the OpenSTLinux SDK.

7.2.2. Download the OpenSTLinux Developer Package

The OpenSTLinux Developer Package, containing all the BSP components source code, must be downloaded and extracted, refer

• first to STM32MPU_Developer_Package#Installing_the_Starter_Package,
• then to the STM32MPU_Developer_Package#Installing_the_OpenSTLinux_BSP_packages chapter only).

7.2.2.1. Download the X-LINUX-RT meta layer

Clone the meta-st-x-linux-rt git repository

cd <Developer Package installation directory>
git clone https://github.com/STMicroelectronics/meta-st-x-linux-rt.git -b openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06

7.2.3. Apply X-LINUX-RT delivery sources

All BSP components are impacted:

• Linux kernel is patched and its configuration has been updated for the RT feature
  
• New DT files are used. External DT repository has been patched and then new DT files are available

7.2.3.1. Apply patches on the Linux kernel

The patches delivered in <Developer Package installation directory>/meta-st-x-linux-rt/recipes-kernel/linux/6.6/6.6.48 must be applied.

For that :

• Enter into the directory containing the Linux kernel sources and apply the patches:

for p in `ls -1 <Developer Package installation directory>/meta-st-x-linux-rt/recipes-kernel/linux/6.6/6.6.48/*.patch`; do patch -p1 < $p; done

Once the patches applied, new fragments are present inside the Linux kernel source.

• Apply first the fragments as explained in the README.HOW_TO.txt helper file. This file is present in the Linux kernel installation directory.

• Only for STM32MP13x lines , apply the fragment <Developer Package installation directory>/stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/arm-ostl-linux-gnueabilinux-stm32mp-6.6.48-stm32mp-r1-r0/optional-fragment-06-nosmp.config.

• Then, add also the following fragments:
  

* <Linux kernel source code directory>/arch/arm/configs/fragment-07-rt.config
* <Linux kernel source code directory>/arch/arm/configs/fragment-07-rt-sysvinit.config
* <Developer Package installation directory/meta-st-x-linux-rt/recipes-kernel/linux/6.6/fragment-10-network-improvment.config
* <Developer Package installation directory>/meta-st-x-linux-rt/recipes-kernel/linux/6.6/fragment-11-no-psi.config
* <Developer Package installation directory>/meta-st-x-linux-rt/recipes-kernel/linux/6.6/fragment-12-rt-optimization.config

• The Linux kernel can now be built and deployed, as explained in Building and deploying the Linux kernel for the first time.

7.2.3.2. Apply patches on the external device tree

The patches delivered in <Developer Package installation directory>/meta-st-x-linux-rt/recipes-extended/external-dt/external-dt must be applied. For that:
Enter into the directory containing the external device tree sources and apply the patches:

for p in `ls -1 <Developer Package installation directory>/meta-st-x-linux-rt/recipes-extended/external-dt/external-dt/*.patch`; do patch -p1 < $p; done

Once the patches are applied, 5 new device tree files are provided to ease the configuration for RT feature:

• stm32mp157f-dk2-rt.dts (for STM32MP157F-DK2 ) sets the CPU clock at 650MHz and disable secure IWDG1
• stm32mp157f-ev1-rt.dts (forSTM32MP157F-EV1 ) sets the CPU clock at 650MHz and disable secure IWDG1
• stm32mp135f-dk-rt.dts (for STM32MP135F-DK ) sets the CPU clock at 900MHz and disable secure IWDG1
• stm32mp257f-dk-rt.dts (for STM32MP257F-DK ) disable secure IWDG1
• stm32mp257f-ev1-rt.dts (for STM32MP257F-EV1 ) disable secure IWDG1

7.2.3.2.1. For STM32MP1 series

For STM32MP1 series

External device tree is not delivered in the OpenSTLinux Developer Package for STM32MP1 series but it can be added, for that :

• Downloaded it from GitHub.

git clone https://github.com/STMicroelectronics/dt-stm32mp.git -b openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06

• export the path into the variable

export EXTDT_DIR=$PWD/dt-stm32mp

• Define a directory for build binaries and fip

export FIP_DEPLOYDIR_ROOT=<Developer Package installation directory>/stm32mp1-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/arm-ostl-linux-gnueabi/fipRT

• Then OP-TEE OS, TF-A and U-Boot must be built with the chosen device tree.

Example for stm32mp157f-dk2-rt.dts

• OP-TEE OS

The Makefile.sdk must be modified to enable external device tree. For that, change the line:

EXTRA_OEMAKE = PLATFORM=stm32mp1 CROSS_COMPILE_core=arm-ostl-linux-gnueabi- CROSS_COMPILE_ta_arm64=arm-ostl-linux-gnueabi- ARCH=arm CFG_ARM32_core=y CROSS_COMPILE_ta_arm32=arm-ostl-linux-gnueabi- NOWERROR=1 LDFLAGS=  CFG_TEE_CORE_LOG_LEVEL=2 CFG_TEE_CORE_DEBUG=n  CFG_SCMI_SCPFW=n

into

EXTRA_OEMAKE = PLATFORM=stm32mp1 CROSS_COMPILE_core=arm-ostl-linux-gnueabi- CROSS_COMPILE_ta_arm64=arm-ostl-linux-gnueabi- ARCH=arm CFG_ARM32_core=y CROSS_COMPILE_ta_arm32=arm-ostl-linux-gnueabi- NOWERROR=1 LDFLAGS=  CFG_TEE_CORE_LOG_LEVEL=2 CFG_TEE_CORE_DEBUG=n  CFG_SCMI_SCPFW=n CFG_EXT_DTS=$(EXTDT_DIR)/optee

OP-TEE OS can now be built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/optee CFG_EMBED_DTB_SOURCE_FILE=stm32mp157f-dk2-rt optee

• U-Boot

The Makefile.sdk must be modified to enable external device tree. For that, change the line:

EXTERNAL_DT_OPTS =

into

EXTERNAL_DT_OPTS = EXT_DTS=$(EXTDT_DIR)/u-boot

U-Boot can now be built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/u-boot UBOOT_CONFIG=default UBOOT_DEFCONFIG=stm32mp15_defconfig UBOOT_BINARY=u-boot.dtb DEVICETREE=stm32mp157f-dk2-rt uboot

• TF-A

The Makefile.sdk must be modified to enable external device tree. For that, change the line:

EXTRA_OEMAKE ?=  PLAT=stm32mp1 ARCH=aarch32 ARM_ARCH_MAJOR=7 CROSS_COMPILE=arm-ostl-linux-gnueabi- DEBUG=1 LOG_LEVEL=40 

into

EXTRA_OEMAKE ?=  PLAT=stm32mp1 ARCH=aarch32 ARM_ARCH_MAJOR=7 CROSS_COMPILE=arm-ostl-linux-gnueabi- DEBUG=1 LOG_LEVEL=40 TFA_EXTERNAL_DT=$(EXTDT_DIR)/tf-a

TF-A can now be built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/arm-trusted-firmware TF_A_DEVICETREE=stm32mp157f-dk2-rt TF_A_CONFIG=optee-sdcard ELF_DEBUG_ENABLE='1' stm32

Then generate the fip

make -f $PWD/../Makefile.sdk TF_A_DEVICETREE=stm32mp157f-dk2-rt TF_A_CONFIG=optee-sdcard ELF_DEBUG_ENABLE='1' DEPLOYDIR=${FIP_DEPLOYDIR_ROOT} fip

The new TF-A and FIP binaries can now be deployed, as explained in Building and deploying the TF-A for the first time.

7.2.3.2.2. For STM32MP2 series

For STM32MP2 series

External device tree is delivered in the OpenSTlinux Developer Package for STM32MP2 series.

As written in its README.HOW_TO.txt, export its path into the variable

export EXTDT_DIR=$PWD
popd

Define a directory for build binaries and fip

export FIP_DEPLOYDIR_ROOT=<Developer Package installation directory>/stm32mp2-openstlinux-6.6-yocto-scarthgap-mpu-v24.11.06/sources/aarch64-ostl-linux/fipRT

Then OP-TEE OS, TF-A and U-Boot must be built with the chosen device tree.

Example for stm32mp257f-ev1-rt.dts

• OP-TEE OS

OP-TEE OS can be built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/optee CFG_EMBED_DTB_SOURCE_FILE=stm32mp257f-ev1-rt optee

• U-Boot

U-Boot can be built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/u-boot UBOOT_CONFIG=default UBOOT_DEFCONFIG=stm32mp25_defconfig UBOOT_BINARY=u-boot.dtb DEVICETREE=stm32mp257f-ev1-rt uboot

• TF-A

TF-A can now built with the specific device tree

make -f $PWD/../Makefile.sdk DEPLOYDIR=${FIP_DEPLOYDIR_ROOT}/arm-trusted-firmware TF_A_DEVICETREE=stm32mp257f-ev1-rt TF_A_CONFIG=optee-sdcard ELF_DEBUG_ENABLE='1' stm32

Then generate the fip

make -f $PWD/../Makefile.sdk TF_A_DEVICETREE=stm32mp257f-ev1-rt TF_A_CONFIG=optee-sdcard ELF_DEBUG_ENABLE='1' DEPLOYDIR=${FIP_DEPLOYDIR_ROOT} fip

The new TF-A and FIP binaries can now be deployed, as explained in Building and deploying the TF-A for the first time.

Real-time

Microprocessor unit

Linux^® is a registered trademark of Linus Torvalds.

Open portable trusted execution environment

Operating system

Symetric multiprocessing

High speed internal oscillator (STM32 clock source) or High speed synchronous serial interface (MIPI^® Alliance standard)

Flash memory shortened to gain space in titles, tables and block diagrams

Board support package

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)c

Device tree

Central processing unit

Firmware image package is a packaging format used by TF-A

Trusted firmware for Arm^® Cortex^®-A

Das U-Boot -- the universal boot loader (see U-Boot)

Trusted execution environment

System control and management interface

Device tree source (in software context) or digital temperature sensor (in peripheral context)

Device tree binary (or Blob)

Executable and linkable file

Real-time

Microprocessor unit

Linux^® is a registered trademark of Linus Torvalds.

Open portable trusted execution environment

Operating system

Symetric multiprocessing

High speed internal oscillator (STM32 clock source) or High speed synchronous serial interface (MIPI^® Alliance standard)

Flash memory shortened to gain space in titles, tables and block diagrams

Board support package

Software development kit (A programming package that enables a programmer to develop applications for a specific platform.)c

Device tree

Central processing unit

Firmware image package is a packaging format used by TF-A

Trusted firmware for Arm^® Cortex^®-A

Das U-Boot -- the universal boot loader (see U-Boot)

Trusted execution environment

System control and management interface

Device tree source (in software context) or digital temperature sensor (in peripheral context)

Device tree binary (or Blob)

Executable and linkable file

Mobile Industry Processor Interface, open membership organization that includes leading companies in the mobile industry that share the objective of defining and promoting open specifications for interfaces inside mobile terminals, see MIPI^® Alliance standard web site https://www.mipi.org

Flash memories combine high density and cost effectiveness of EPROMs with the electrical erasability of EEPROMs. For this reason, the Flash memory market is one of the most exciting areas of the semiconductor industry today and new applications requiring in system reprogramming, such as cellular telephones, automotive engine management systems, hard disk drives, PC BIOS software for Plug & Play, digital TV, set top boxes, fax and other modems, PC cards and multimedia CD-ROMs, offer the prospect of very high volume demand.

Arm^® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

Cortex^®