1. Article purpose[edit source]
This article provides simple examples for the Distribution Package of the OpenSTLinux distribution, that illustrate the cross-compilation with the devtool and BitBake tools:
- modification with Linux® Kernel (configuration, device tree, driver, ...)
- modification of an external in-tree Linux Kernel module
- modification of U-Boot
- modification of TF-A
- addition of software
These examples also show how to deploy the results of the cross-compilation on the target, through a network connection to the host machine.
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All the examples described on this page use devtool and/or bitbake from OpenEmbededded, see OpenEmbedded - devtool for more information. |
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There are many ways to achieve the same result; this article aims to provide at least one solution per example. You have the liberty to explore other methods that are better adapted to your development constraints. |
2. Prerequisites[edit source]
The prerequisites from Installing the OpenSTLinux distribution must be executed.
The board and the host machine are connected through an Ethernet link, and a remote terminal program is started on the host machine: see How to get Terminal.
The target is started, and its IP address (<board ip address>) is known.
3. Modification with kernel[edit source]
3.1. Preamble[edit source]
To start modification with a module, you need to initialize your Distribution Package environment.
PC $> cd <working directory path of distribution>
PC $> DISTRO=openstlinux-weston MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh
You are now in the build directory, identified by <build dir> in the following paragraphs.
Initialize devtool for kernel component:
PC $> devtool modify virtual/kernel
NOTE: Starting bitbake server...
NOTE: Creating workspace layer in /mnt/internal_storage/oetest/oe_openstlinux_rocko/build-openstlinuxweston-stm32mp1/workspace
NOTE: Enabling workspace layer in bblayers.conf
Parsing recipes: 100% |########################################################################################| Time: 0:00:54
Parsing of 2401 .bb files complete (0 cached, 2401 parsed). 3282 targets, 88 skipped, 0 masked, 0 errors.
NOTE: Mapping virtual/kernel to linux-stm32mp
NOTE: Resolving any missing task queue dependencies
...
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For the case of virtual/<something> component, you need to get the name of mapping between virtual component and associated recipe. In this example, the name of kernel recipe is indicated in the trace, but you can also get it by calling devtool status
A minority of devtool command supports the virtual/<something> component, like devtool modify, it is why you need to get the recipe name associated to virtual/component. |
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The source code of kernel is located on <build dir>/workspace/sources. You can change the path where the source code is extracted by customizing the devtool modify command |
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For all the work around the kernel, we strongly encourage some usage for deploying the binaries on board
The difference of usage comes from the number of files to deploy on board. When there is only one or two files to put on board, the easiest way to do it is to deploy only the desired files . |
3.2. Modifying kernel configuration[edit source]
This simple example modifies the kernel configuration via menuconfig for the CMA size.
- Get the current value of the CMA size (128 Mbytes here) through the analysis of the target boot log
Board $> dmesg | grep -i cma
[ 0.000000] cma: Reserved 128 MiB at 0xf0000000
- Start the Linux kernel configuration menu: see Menuconfig or how to configure kernel
- Navigate to "Device Drivers - Generic Driver Options"
- select "Size in Megabytes"
- modify its value to 256
- exit and save the new configuration
- Check that the configuration file (.config) has been modified
PC $> grep -i CONFIG_CMA_SIZE_MBYTES <build dir>/workspace/sources/<name of kernel recipe>/.config.new
CONFIG_CMA_SIZE_MBYTES=256
- Cross-compile the Linux kernel: see Menuconfig or how to configure kernel
- Update the Linux kernel image on board: see Menuconfig or how to configure kernel
- Reboot the board: see Menuconfig or how to configure kernel
- Get the new value of the CMA size (256 Mbytes) through the analysis of the target boot log
Board $> dmesg | grep -i cma [ 0.000000] cma: Reserved 256 MiB at 0xe0000000
3.3. Modifying the Linux kernel device tree[edit source]
This simple example modifies the default status of a user LED.
- With the board started; check that the user LED (LD3) is disabled
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/ directory
PC $> cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the arch/arm/boot/dts/stm32mp157c-ed1.dts Device Tree Source file for evaluation board or
Edit the arch/arm/boot/dts/stm32mp157c-dk2.dts Device Tree Source file for discovery board or
- Change the status of the "stm32mp:green:user" led to "okay", and set its default state to "on"
led { compatible = "gpio-leds"; status = "okay"; red { label = "stm32mp:red:status"; gpios = <&gpioa 13 GPIO_ACTIVE_LOW>; status = "disabled"; }; green { label = "stm32mp:green:user"; gpios = <&gpioa 14 GPIO_ACTIVE_LOW>; default-state = "on"; status = "okay"; }; };
- Go to the build directory
PC $> cd <build dir>
If this update is accepted, then to report in other paragraph of this page}}
- Generate the device tree blobs (*.dtb)
PC $> bitbake virtual/kernel -C compile
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we use here bitbake command instead of devtool build because the build makes compile, compile_kernemodules and install commands whereas we only need only compile command to generate the kernel image and the device tree |
- Update the device tree blobs on the board
PC $> scp <build dir>/tmp-glibc/deploy/images/<machine name>/*.dtb root@<board ip address>:/boot
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If the /boot mounting point doesn't exist yet, please see how to create a mounting point |
- Reboot the board
Board $> cd /boot; sync; systemctl reboot
- Check that the user LED (LD3) is enabled (green)
3.4. Modifying a built-in Linux kernel device driver[edit source]
This simple example adds unconditional log information when the display driver is probed.
- Check that there is no log information when the display driver is probed
Board $> dmesg | grep -i stm_drm_platform_probe
Board $>
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/
PC $> cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the ./drivers/gpu/drm/stm/drv.c source file
- Add a log information in the stm_drm_platform_probe function
static int stm_drm_platform_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; struct drm_device *ddev; int ret; [...] DRM_INFO("Simple example - %s\n", __func__); return 0; [...] }
- Go to the build directory
PC $> cd <build dir>
- Cross-compile the Linux kernel
PC $> bitbake virtual/kernel -C compile
- Update the Linux kernel image on board
PC $> scp <build dir>/tmp-glibc/deploy/images/<machine name>/uImage root@<board ip address>:/boot
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If the /boot mounting point doesn't exist yet, please see how to create a mounting point |
- Reboot the board
Board $> cd /boot; sync; systemctl reboot
- Check that there is now log information when the display driver is probed
Board $> dmesg | grep -i stm_drm_platform_probe [ 5.005833] [drm] Simple example - stm_drm_platform_probe
3.5. Modifying/adding an external Linux kernel module[edit source]
Most device drivers (modules) in the Linux kernel can be compiled either into the kernel itself (built-in/internal module) or as Loadable Kernel Modules (LKM/external module) that need to be placed in the root file system under the /lib/modules directory. An external module can be in-tree (in the kernel tree structure), or out-of-tree (outside the kernel tree structure).
This simple example adds an unconditional log information when the virtual video test driver (vivid) kernel module is probed or removed.
- Go to the <build dir>/workspace/sources/<name of kernel recipe>/
PC $> cd <build dir>/workspace/sources/<name of kernel recipe>/
- Edit the ./drivers/media/platform/vivid/vivid-core.c source file
- Add log information in the vivid_probe and vivid_remove functions
static int vivid_probe(struct platform_device *pdev) { const struct font_desc *font = find_font("VGA8x16"); int ret = 0, i; [...] /* n_devs will reflect the actual number of allocated devices */ n_devs = i; pr_info("Simple example - %s\n", __func__); return ret; }
static int vivid_remove(struct platform_device *pdev) { struct vivid_dev *dev; unsigned int i, j; [...] pr_info("Simple example - %s\n", __func__); return 0; }
- Go to the build directory
PC $> cd <build dir>
- Cross-compile the Linux kernel modules
PC $> bitbake virtual/kernel -C compile
- Update the vivid kernel module on the board
PC $> devtool deploy-target -Ss <name of kernel recipe> root@<board ip address>:/
- Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory
Board $> /sbin/depmod -a
Board $> sync
- Insert the vivid kernel module into the Linux kernel
Board $> modprobe vivid [...] [ 3412.784638] Simple example - vivid_probe
- Remove the vivid kernel module from the Linux kernel
Board $> rmmod vivid [...] [ 3423.708517] Simple example - vivid_remove
4. Adding an external out-of-tree Linux kernel module[edit source]
This simple example adds a "Hello World" external out-of-tree Linux kernel module to the Linux kernel.
- Create a directory for this kernel module example
PC $> mkdir kernel_module_example
PC $> cd kernel_module_example
- Create the source code file for this kernel module example: kernel_module_example.c
// SPDX-identifier: GPL-2.0
/*
* Copyright (C) STMicroelectronics SA 2018
*
* Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
*
*/
#include <linux/module.h> /* for all kernel modules */
#include <linux/kernel.h> /* for KERN_INFO */
#include <linux/init.h> /* for __init and __exit macros */
static int __init kernel_module_example_init(void)
{
printk(KERN_INFO "Kernel module example: hello world from STMicroelectronics\n");
return 0;
}
static void __exit kernel_module_example_exit(void)
{
printk(KERN_INFO "Kernel module example: goodbye from STMicroelectronics\n");
}
module_init(kernel_module_example_init);
module_exit(kernel_module_example_exit);
MODULE_DESCRIPTION("STMicroelectronics simple external out-of-tree Linux kernel module example");
MODULE_AUTHOR("Jean-Christophe Trotin <jean-christophe.trotin@st.com>");
MODULE_LICENSE("GPL v2");
- Create the makefile for this kernel module example: Makefile
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All the indentations in a makefile are tabulations |
# Makefile for simple external out-of-tree Linux kernel module example # Object file(s) to be built obj-m := kernel_module_example.o # Path to the directory that contains the Linux kernel source code # and the configuration file (.config) KERNEL_DIR ?= <Linux kernel path> # Path to the directory that contains the source file(s) to compile PWD := $(shell pwd) default: $(MAKE) -C $(KERNEL_DIR) M=$(PWD) modules clean: $(MAKE) -C $(KERNEL_DIR) M=$(PWD) clean
- Add a new recipe to the workspace
PC $> cd <build dir>
PC $> devtool add mymodule kernel_module_example/
- Adapt recipe to kernel module build
PC $> devtool edit-recipe mymodule
- Modify the recipe according the following changes (see highlighted lines)
# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)
# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""
# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""
# NOTE: this is a Makefile-only piece of software, so we cannot generate much of the
# recipe automatically - you will need to examine the Makefile yourself and ensure
# that the appropriate arguments are passed in.
DEPENDS = "virtual/kernel"
inherit module
EXTRA_OEMAKE = "ARCH=arm"
EXTRA_OEMAKE += "KERNEL_DIR=${STAGING_KERNEL_BUILDDIR}"
S = "${WORKDIR}"
do_configure () {
# Specify any needed configure commands here
:
}
do_compile () {
# You will almost certainly need to add additional arguments here
oe_runmake
}
do_install () {
# NOTE: unable to determine what to put here - there is a Makefile but no
# target named "install", so you will need to define this yourself
install -d ${D}/lib/modules/${KERNEL_VERSION}
install -m 0755 ${B}/kernel_module_example.ko ${D}/lib/modules/${KERNEL_VERSION}/
}
- Go to the build directory
PC $> cd <build dir>
- Generated kernel module example
PC $> devtool build mymodule
- Push this kernel module example on board
PC $> devtool deploy-target -Ss mymodule root@<board ip address>
- Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory
Board $> /sbin/depmod -a
Board $> sync
- Insert the kernel module example into the Linux kernel
Board $> modprobe kernel_module_example [18167.821725] Kernel module example: hello world from STMicroelectronics
- Remove the kernel module example from the Linux kernel
Board $> rmmod kernel_module_example [18180.086722] Kernel module example: goodbye from STMicroelectronics
5. Modifying the U-Boot[edit source]
This simple example adds unconditional log information when U-Boot starts. Within the scope of the trusted boot chain, U-Boot is used as second stage boot loader (SSBL).
- Have a look at the U-Boot log information when the board reboots
Board $> reboot [...] U-Boot <U-Boot version> CPU: STM32MP1 rev1.0 Model: STMicroelectronics STM32MP157C [...] Board: stm32mp1 in trusted mode [...]
- Go to the build directory
PC $> cd <build dir>
- Search U-boot recipe
PC $> devtool search u-boot*
u-boot-stm32mp-extlinux Generate 'extlinux.conf' file for U-boot
u-boot-stm32mp Universal Boot Loader for embedded devices for stm32mp
On this example, the recipe name is u-boot-stm32mp
- Start to work with u-boot
PC $> devtool modify u-boot-stm32mp
Example:
PC $> cd <build dir>/workspace/sources/u-boot-stm32mp
- Edit the ./board/st/stm32mp1/stm32mp1.c source file
- Add a log information in the checkboard function
int checkboard(void) { char *mode; [...] printf("Board: stm32mp1 in %s mode\n", mode); printf("U-Boot simple example\n"); return 0; }
- Cross-compile the U-Boot: trusted boot
PC $> devtool build u-boot-stm32mp
PC $> bitbake u-boot-stm32mp -c deploy
- Go to the directory in which the compilation results are stored
PC $> cd <build dir>/tmp-glibc/deploy/images/<machine name>/
- Reboot the board, and hit any key to stop in the U-boot shell
Board $> reboot
[...]
Hit any key to stop autoboot: 0
STM32MP>
- Connect a USB cable between the host machine and the board via the USB OTG ports
- In the U-Boot shell, call the USB mass storage function
STM32MP> ums 0 mmc 0
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for more information about the usage of U-Boot UMS functionality, see How to use USB mass storage in U-Boot |
- On the host machine, check the partition associated with the secondary stage boot loader (ssbl): sdc3 here
PC $> ls -l /dev/disk/by-partlabel/ total 0 lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4 lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl1 -> ../../sdc1 lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl2 -> ../../sdc2 lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5 lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3 lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6
- Copy the binary (u-boot.stm32) to the dedicated partition
PC $> dd if=u-boot-<board name>-trusted.stm32 of=/dev/sdc3 bs=1M conv=fdatasync
(here u-boot-stm32mp157c-ev1-trusted.stm32 or u-boot-stm32mp157c-dk2-trusted.stm32)
- Reset the U-Boot shell
STM32MP> reset
- Have a look at the new U-Boot log information when the board reboots
[...] U-Boot <U-Boot version> CPU: STM32MP1 rev1.0 Model: STMicroelectronics STM32MP157C [...] Board: stm32mp1 in trusted mode U-Boot simple example [...]
6. Modifying the TF-A[edit source]
This simple example adds unconditional log information when the TF-A starts. Within the scope of the trusted boot chain, TF-A is used as first stage boot loader (FSBL).
- Have a look at the TF-A log information when the board reboots
Board $> reboot [...] INFO: System reset generated by MPU (MPSYSRST) INFO: Using SDMMC [...]
- Go to the build directory
PC $> cd <build dir>
- Search TF-A recipe
PC $> devtool search tf-a* babeltrace Babeltrace - Trace Format Babel Tower libunistring Library for manipulating C and Unicode strings lttng-tools Linux Trace Toolkit Control gettext Utilities and libraries for producing multi-lingual messages glibc GLIBC (GNU C Library) tf-a-stm32mp Trusted Firmware-A for STM32MP1 gnutls GNU Transport Layer Security Library gstreamer1.0 GStreamer 1.0 multimedia framework harfbuzz Text shaping library glibc-locale Locale data from glibc kbd Keytable files and keyboard utilities
On this example, the recipe name is tf-a-stm32mp
- Start to work with tf-a
PC $> devtool modify tf-a-stm32mp
- Go to <build dir>/workspace/sources/tf-a-stm32mp
PC $> cd <build dir>/workspace/sources/tf-a-stm32mp
- Edit the ./plat/st/stm32mp1/bl2_io_storage.c source file
- Add a log information in the stm32mp1_io_setup function
void stm32mp1_io_setup(void) { int io_result; [...] /* Add a trace about reset reason */ print_reset_reason(); INFO("TF-A simple example"); [...] }
- Cross-compile the TF-A
PC $> devtool build tf-a-stm32mp
PC $> bitbake tf-a-stm32mp -c deploy
- Go to the directory in which the compilation results are stored
PC $> cd <build dir>/tmp-glibc/deploy/images/<machine name>/
- Reboot the board, and hit any key to stop in the U-boot shell
Board $> reboot
[...]
Hit any key to stop autoboot: 0
STM32MP>
- Connect a USB cable between the host machine and the board via the USB OTG ports
- In the U-Boot shell, call the USB mass storage function
STM32MP> ums 0 mmc 0
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for more information about the usage of U-boot ums functionality see How to use USB mass storage in U-Boot |
- On the host machine, check the partition associated with the first stage boot loader (fsbl1 and fsbl2 as backup): sdc1 and sdc2 (as backup) here
PC $> ls -l /dev/disk/by-partlabel/ total 0 lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4 lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl1 -> ../../sdc1 lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl2 -> ../../sdc2 lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5 lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3 lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6
- Copy the binary (tf-a-stm32mp157c-ev1-trusted.stm32) to the dedicated partition; to test the new TF-A binary, it might be useful to keep the old TF-A binary in the backup FSBL (fsbl2)
PC $> dd if=tf-a-<board name>-trusted.stm32 of=/dev/sdc1 bs=1M conv=fdatasync
(here tf-a-stm32mp157c-ev1-trusted.stm32 or tf-a-stm32mp157c-dk2-trusted.stm32)
- Reset the U-Boot shell
STM32MP> reset
- Have a look at the new TF-A log information when the board reboots
[...] INFO: System reset generated by MPU (MPSYSRST) INFO: TF-A simple example INFO: Using SDMMC [...]
7. Adding a "hello world" user space example[edit source]
This chapter shows how to compile and execute a simple "hello world" example.
- Create a directory for this user space example
PC $> mkdir hello_world_example
PC $> cd hello_world_example
- Create the source code file for this user space example: hello_world_example.c
// SPDX-identifier: GPL-2.0
/*
* Copyright (C) STMicroelectronics SA 2018
*
* Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
*
*/
#include <stdio.h>
#include <unistd.h>
int main(int argc, char **argv)
{
int i =11;
printf("\nUser space example: hello world from STMicroelectronics\n");
setbuf(stdout,NULL);
while (i--) {
printf("%i ", i);
sleep(1);
}
printf("\nUser space example: goodbye from STMicroelectronics\n");
return(0);
}
- Add a new recipe to the workspace
PC $> cd <build dir>
PC $> devtool add myhelloword hello_world_example/
- Adapt recipe
PC $> devtool edit-recipe myhelloword
- Modify the recipe according the following changes (see highlighted lines)
# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)
# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""
# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""
# NOTE: no Makefile found, unable to determine what needs to be done
do_configure () {
# Specify any needed configure commands here
:
}
do_compile () {
# Specify compilation commands here
cd ${S}
${CC} hello_world_example.c -o hello_word_example
}
do_install () {
# Specify install commands here
install -d ${D}${bindir}
install -m 755 ${S}/hello_word_example ${D}${bindir}/
}
- Compile binary
PC $> devtool build myhelloword
- Push this binary on board
PC $> devtool deploy-target -s myhelloword root@<board ip address>
- Execute this user space example
Board $> /usr/bin/hello_world_example User space example: hello world from STMicroelectronics 10 9 8 7 6 5 4 3 2 1 0 User space example: goodbye from STMicroelectronics
8. Tips[edit source]
8.1. Creating a mounting point[edit source]
The objective is to create a mounting point for the boot file system (bootfs partition)
- Find the partition label associated with the boot file system
Board $> ls -l /dev/disk/by-partlabel/ total 0 lrwxrwxrwx 1 root root 15 Dec 13 12:31 bootfs -> ../../mmcblk0p4 lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl1 -> ../../mmcblk0p1 lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl2 -> ../../mmcblk0p2 lrwxrwxrwx 1 root root 15 Dec 13 12:31 rootfs -> ../../mmcblk0p5 lrwxrwxrwx 1 root root 15 Dec 13 12:31 ssbl -> ../../mmcblk0p3 lrwxrwxrwx 1 root root 15 Dec 13 12:31 userfs -> ../../mmcblk0p6
- Attach the boot file system found under /dev/mmcblk0p4 in the directory /boot
Board $> mount /dev/mmcblk0p4 /boot
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