General discussions

If you’re working on embedded Linux projects and need a lightweight, efficient way to integrate LVGL into your system, you’ll be happy to know that we’ve written a comprehensive guide that has been merged into the official LVGL documentation to assist you.

Buildroot philosophy

Buildroot is designed with a keep it simple philosophy, focusing on generating small, efficient, and easily reproducible embedded Linux systems.

Unlike more complex build systems, Buildroot does not use a traditional package management system. Instead, it rebuilds selected components from source as needed, ensuring a clean and controlled environment.

Its configuration system is inspired by the Linux kernel’s menuconfig, allowing developers to easily select packages and customize their system with minimal overhead. The objective is to provide a fast, deterministic, and low-maintenance way to build embedded Linux images, making it an excellent choice for projects where simplicity and quick iteration matter.

Why Use Buildroot Instead of a Yocto Recipe?

While Yocto is a powerful tool for creating custom Linux distributions, Buildroot offers a simpler and more lightweight approach, making it ideal for many embedded projects. Here are some advantages.

• Faster build times: Buildroot uses a straightforward dependency system, avoiding the complexity of Yocto’s layers and recipes.
• Easy to configure: No need to dive into bitbake and complex metadata; just tweak a simple configuration file.
• Minimal system footprint: Buildroot produces leaner images, making it great for resource-constrained devices.
• Simpler learning curve: Developers new to embedded Linux will find Buildroot easier to grasp than Yocto.

Getting started with LVGL in Buildroot

While there is no official LVGL package in Buildroot, the LVGL documentation provides a complete guide on how to build a Buildroot-based system and integrate LVGL into your project. The guide includes an example using the Raspberry Pi 4, but the same approach can be applied to other platforms.

The process involves: 1️⃣ Building a Buildroot system: Configuring and generating a minimal embedded Linux image tailored for your hardware. 2️⃣ Using the generated SDK: Cross-compiling your LVGL application with the Buildroot-provided toolchain. 3️⃣ Embedding the application: Leveraging a rootfs overlay to easily include your compiled application in the final root filesystem.

Check out the official LVGL Buildroot documentation for a step-by-step guide here.

If you’re already using Buildroot or considering it for your next project, give LVGL a try and let us know how it works for you! 🚀

What are your thoughts on using Buildroot for LVGL vs. Yocto? Let’s discuss!

Last week, I had to work on a project that is using the Renesas RA8D1 ‘Graphics micro controller’.

The use of the e2studio IDE is required in this project – so I’ve installed it with latest FSP included and read the documentation on how use to use it.

The next step was creating a Renesas account, after the successful installation on the first launch of e2studio it prompted me to login – And it failed with some “crypto error”, didn’t spend too much time figuring out what went wrong.

To be honest, I was expecting a subpar experience because one of my colleagues had issues with running e2studio on Ubuntu 22.04, it was mostly crashing for no apparent reason.

I am using the same version of Ubuntu, but a couple of months ago I’ve switched to a different graphical environment, and I did of course experience some crashes when using e2studio – but much less often.

Due to the complexity of desktop software, there could be many reasons to this observation. Maybe he has using a slightly older version of e2studio from a couple of months ago.

Searching ‘Wayland + eclipse + crash’ on google yields a lot of results – Wayland support is an ongoing effort for Java applications

The story took a sad turn when I really needed to use JLinkRTTViewer and realized – it only has support for X11…

Indeed, when I compiled the graphical environment I was lazy and couldn’t be bothered including Xwayland support.

So I can not run X11 applications. I will have to re-configure and recompile it with Xwayland support enabled – stuff that is typically done on the weekend if the weather is bad and there is nothing more interesting to do 😀

But I had to get work done right then and there. 😅 To get around this road block in a quick manner, I’ve just installed Xfce4 and logged in.

Trying out e2studio in Xfce4 was a very pleasant experience, it feels much more responsive and it hasn’t crashed even once.

There is a J-Link progress bar that appears when flashing – that I didn’t see when my colleague used e2studio on Ubuntu 22.04

The moral of the story is that from now on I will use the Xfce4 an X11 desktop environment when working on STM or Renesas projects. For me, X11 is not going away anytime soon.

grep is a utility program available on any Unix-like operating system.

The most common use of the grep utility, is to look for a matching string in a file or

with the use of the -r option, directories of files

grep -rn variable_name ./src

grep -rn variable_name ./src

The -n option makes it prints out line numbers and the file path relative to the

current working directory

Another common use is finding the large files on a system,

very practical when one runs out of storage space.

du -h ~/Downloads | grep ^[0-9.]*[G]
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default/cache2/entries
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default/cache2
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla
1.1G	/home/etag/Downloads/snap/firefox/common/.cache
1.9G	/home/etag/Downloads/snap/firefox/common
1.9G	/home/etag/Downloads/snap/firefox
1.3G	/home/etag/Downloads/snap/teams-for-linux
3.8G	/home/etag/Downloads/snap
6.7G	/home/etag/Downloads/archives
1.4G	/home/etag/Downloads/cube_mx
31G	/home/etag/Downloads/

du -h ~/Downloads | grep ^[0-9.]*[G]
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default/cache2/entries
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default/cache2
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox/szwshp2r.default
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla/firefox
1.1G	/home/etag/Downloads/snap/firefox/common/.cache/mozilla
1.1G	/home/etag/Downloads/snap/firefox/common/.cache
1.9G	/home/etag/Downloads/snap/firefox/common
1.9G	/home/etag/Downloads/snap/firefox
1.3G	/home/etag/Downloads/snap/teams-for-linux
3.8G	/home/etag/Downloads/snap
6.7G	/home/etag/Downloads/archives
1.4G	/home/etag/Downloads/cube_mx
31G	/home/etag/Downloads/

It printed all directories that are larger than 1 gigabyte

du is a utility that estimates the storage space of files or directories, in this example only directories

and the -h option makes it print the size in a human friendly format.

The output of the du utility is then passed to the standard input of grep which

filters it by applying a simple regular expression ^[0-9.]*G

The text must begin with any number of characters matching the range 0-9 and the dot . followed

by a single capital letter G

The caret ^ means ‘beginning of the line’

The brackets [0-9.] are used to specify a character class, ranges can be used like ‘A-z’ ‘A-Z’ ‘0-9’ which is

of course more practical than typing out [0123456789] each time.

The asterisk * means zero or more occurrences of the character or character class, if the * is omitted in the above

example it would only match lines beginning with a single digit or dot and followed by a G

* always applies to the previous character or character class

1G
9G
.G

1G
9G
.G

Since the du utility also prints out file names, I often use it to get a list of all files names

of a particular extension. While I agree that the find utility is probably faster and more optimized,

my problem with it is that I can never remember the syntax or options 🙂 So I tend to use it only in scripts

and lookup the manual page each time.

du -a src | grep "\.h$"

du -a src | grep "\.h$"

This outputs a list of all C header files present in the src directory

The dollar sign $ means ‘end of the line’

The dot . ‘means any single character’

Consider the following command

du -a src | grep .h$

du -a src | grep .h$

It would nearly achieve the desired result, it will also print out files ending in sh

so shell scripts and C header files.

To match lines ending in ‘.h’ the dot has to be escaped with a backslash \

to represent the actual character.

Note that the quotes are necessary here, because the shell also makes use of the backslash to escape characters

that have a ‘special meaning’.

One can also use the variant below to prevent the shell from interpreting the backslash

du -a src | grep \\.h$

du -a src | grep \\.h$

The dot is a very powerful concept, let’s print out the first 10 words in the English dictionary

that begin with ‘th’ followed by any 3 letters

grep ^th...$ /usr/dict/en/words.txt | head -n 10
thack
thais
thala
thana
thane
thank
tharf
tharm
thatd
thatn

grep ^th...$ /usr/dict/en/words.txt | head -n 10
thack
thais
thala
thana
thane
thank
tharf
tharm
thatd
thatn

One can find some unusual words 🙂

Another common everyday use of the caret is filtering the output of ls -l

to show only directories

ls -l ~/src/lvgl | grep ^d
drwxrwxr-x 15 etag etag  4096 Dec 28 13:56 demos
drwxrwxr-x  9 etag etag  4096 Dec 28 13:56 docs
drwxrwxr-x  8 etag etag  4096 Dec 16 13:17 env_support
drwxrwxr-x 14 etag etag  4096 Dec 16 13:17 examples
drwxrwxr-x  3 etag etag  4096 Dec 16 13:17 libs
drwxrwxr-x  5 etag etag  4096 Dec 28 13:56 scripts
drwxrwxr-x 17 etag etag  4096 Dec 28 13:56 src
drwxrwxr-x 11 etag etag  4096 Dec 28 13:56 tests
drwxrwxr-x  2 etag etag  4096 Dec 28 13:56 xmls
drwxrwxr-x  2 etag etag  4096 Dec 16 13:17 zephyr

ls -l ~/src/lvgl | grep ^d
drwxrwxr-x 15 etag etag  4096 Dec 28 13:56 demos
drwxrwxr-x  9 etag etag  4096 Dec 28 13:56 docs
drwxrwxr-x  8 etag etag  4096 Dec 16 13:17 env_support
drwxrwxr-x 14 etag etag  4096 Dec 16 13:17 examples
drwxrwxr-x  3 etag etag  4096 Dec 16 13:17 libs
drwxrwxr-x  5 etag etag  4096 Dec 28 13:56 scripts
drwxrwxr-x 17 etag etag  4096 Dec 28 13:56 src
drwxrwxr-x 11 etag etag  4096 Dec 28 13:56 tests
drwxrwxr-x  2 etag etag  4096 Dec 28 13:56 xmls
drwxrwxr-x  2 etag etag  4096 Dec 16 13:17 zephyr

To only show files, one can use the -v option to invert the meaning of the expression

ls -l ~/src/lvgl | grep -v ^d | head -n 6
total 232
-rw-rw-r--  1 etag etag  1518 Dec 28 13:56 CMakeLists.txt
-rw-rw-r--  1 etag etag  2818 Dec 16 13:17 CMakePresets.json
-rw-rw-r--  1 etag etag  2508 Dec 16 13:17 component.mk
-rw-rw-r--  1 etag etag   204 Dec 16 13:17 idf_component.yml
-rw-rw-r--  1 etag etag 57414 Dec 28 13:56 Kconfig

ls -l ~/src/lvgl | grep -v ^d | head -n 6
total 232
-rw-rw-r--  1 etag etag  1518 Dec 28 13:56 CMakeLists.txt
-rw-rw-r--  1 etag etag  2818 Dec 16 13:17 CMakePresets.json
-rw-rw-r--  1 etag etag  2508 Dec 16 13:17 component.mk
-rw-rw-r--  1 etag etag   204 Dec 16 13:17 idf_component.yml
-rw-rw-r--  1 etag etag 57414 Dec 28 13:56 Kconfig

But the if total amount is not needed:

ls -l ~/src/lvgl | grep ^- | head -n 6

ls -l ~/src/lvgl | grep ^- | head -n 6

When working with LVGL, to locate the definition of a function this

expression can be used

grep -rn "^[a-z_\ *]*\ lv_obj_set_size.*[^;/]$" src
src/core/lv_obj_pos.c:213:void lv_obj_set_size(lv_obj_t * obj, int32_t w, int32_t h)

grep -rn "^[a-z_\ *]*\ lv_obj_set_size.*[^;/]$" src
src/core/lv_obj_pos.c:213:void lv_obj_set_size(lv_obj_t * obj, int32_t w, int32_t h)

Let’s break it down, the line must begin with one or more characters defined by the character class [a-z_\ *]

which allows letters underscores spaces and the * character

So, it covers storage specifiers, return types and pointers.

There must be at least a space before the function name which can be followed by any number of characters

but it must not end with ; or /

With the caret ^ omitted from the [;/] character class, it will output

the declaration and calls to the function, this is because the caret inverts the meaning of the

character class

grep -rn "^[a-z_\ *]*\ lv_obj_create.*[;]$" src
src/core/lv_obj.h:229:lv_obj_t * lv_obj_create(lv_obj_t * parent);
src/widgets/tabview/lv_tabview.c:277:    lv_obj_create(obj);
tests/src/test_cases/widgets/test_obj_tree.c:18:    lv_obj_create(lv_screen_active());
tests/src/test_cases/widgets/test_obj_tree.c:20:    lv_obj_create(lv_screen_active());

grep -rn "^[a-z_\ *]*\ lv_obj_create.*[;]$" src
src/core/lv_obj.h:229:lv_obj_t * lv_obj_create(lv_obj_t * parent);
src/widgets/tabview/lv_tabview.c:277:    lv_obj_create(obj);
tests/src/test_cases/widgets/test_obj_tree.c:18:    lv_obj_create(lv_screen_active());
tests/src/test_cases/widgets/test_obj_tree.c:20:    lv_obj_create(lv_screen_active());

To only show declarations, filter it more

grep -rn "^[a-z_\ *]*\ lv_obj_create.*[;]$" src | grep \\.h
src/core/lv_obj.h:229:lv_obj_t * lv_obj_create(lv_obj_t * parent);

grep -rn "^[a-z_\ *]*\ lv_obj_create.*[;]$" src | grep \\.h
src/core/lv_obj.h:229:lv_obj_t * lv_obj_create(lv_obj_t * parent);

This expression works because the coding convention used by LVGL states that

the opening brace { of a function body always goes on the line below

The / is needed because it could match a calls instead

something(); /* some comment */

something(); /* some comment */

Usually expressions depend on the style of the code

some projects, have return types and storage specifiers on a separate line above the function name

void
myfunction(int x, int y)
{
	/* body */
}

void
myfunction(int x, int y)
{
	/* body */
}

In such projects the following expression can be used to locate the definition

grep -rn ^myfunction src

grep -rn ^myfunction src

There are many more use cases for grep, it is a very practical tool that I use on a daily basis.

To filter logs, find occurrences and extract matching strings with the -o option

the only catch is that it can only perform pattern matching on one line at a time.