Thursday, March 26, 2020

Qt on RaspberryPi

Qt on RaspberryPi is really easy, but can be rather time consuming to build an image to run on raspberry pi with Qt 5. You can either do it up yourself manually grabbing the sources, tool chains, etc. You could also buy the Qt for device creation package which comes with great support, bells, whistles and commercial licensing, or build it yourself and use open source GPL licensing. To get started using the open sourced parts, you clone one git repo:
  • meta-boot2qt 
git clone git://

 You then need to decide which device to target. I have a fancy new raspberry pi 4 hooked up to a touch screen, so I will choose that.

To get a list of the Boot2Qt targets run the command:

  meta-boot2qt/b2qt-init-build-env list-devices

To initialize the build environment for a raspberry pi:

 meta-boot2qt/b2qt-init-build-env init --device raspberrypi4

This will clone needed repo's.

You will then need to set up the environment specifically for your device by setting MACHINE
and then source the script:

 export MACHINE=raspberrypi4 
 source ./

Now, if you just want an image to run:

 bitbake b2qt-embedded-qt5-image

Sit back, enjoy a cuppa and a pizza on this fine day... Don't let the computer sleep, or you will kick yourself in a few hours when you check on the progress. My final image to be dd'd onto the sd card was found in


This is what you will be presented with when you boot your device:

To build the sdk/sysroot the command would be:

 bitbake meta-toolchain-b2qt-embedded-qt5-sdk 

You can build other targets including qemu, which will give you an image that runs in the qemu emulator.

You can then also set up target kits in Qt Creator to target the raspberry pi, set up the device kit so you can run and debug on the device. More fun for all that time on your hands right now!

I write about creating device OS images using Qt's Boot To Qt and Bitbake for the Raspeberry Pi in my book, Hands-On Mobile and Embedded Development with Qt 5

Tuesday, March 24, 2020

QtWebAssembly updates Emscripten Requirement

In the just released Qt 5.15-beta2 version, Qt for WebAssembly will require an Emscripten update from 1.38.27 to 1.39.8. Require because there are a few incompatible changes we needed in Qt.

The update includes several improvements, including faster linking times, as Emscripten no longer has to transpile to javascript before it outputs wasm. It can build directly to wasm thanks to upstream wasm support in clang.

Users will notice app build times are greatly improved on all platforms, since Emscripten no longer has a two pass linker procedure.

To update Emscripten, I usually do this from the commandline:

cd ~/emsdk
git pull
./emsdk update-tags
./emsdk install 1.39.8
./emsdk activate --embedded 1.39.8

and finally

source ~/emsdk/

Of course, you will need to rebuild Qt, all other modules and apps.

You can read more about Qt for WebAssembly and Embedded Qt development in the book Hands-On Mobile and Embedded Development with Qt 5