Skip to content

Code, deploy and test using welma-update-gen

This page will show you how to have short development cycles by creating update artifacts and deploying them onto your device.

Prerequisites:

  • a Welma image built and running on your device

See also Deploy your application.

Build the SDK

In your Yocto build environment, you first need to build a Software Development Kit (SDK) that will have the Welma tools:

$ bitbake welma-image-headless-dev -c populate_sdk

You can then install this SDK:

$ tmp/deploy/sdk/welma-glibc-x86_64-welma-image-headless-dev-*-toolchain-1.1.0.sh
Welma by Witekio SDK installer version 1.1.0
============================================
Enter target directory for SDK (default: /opt/welma/1.1.0):
You are about to install the SDK to "/opt/welma/1.1.0". Proceed [Y/n]? 
Extracting SDK...........................................................done
Setting it up...done
SDK has been successfully set up and is ready to be used.

Next, each time you wish to use the SDK in a new shell session, you need to source the environment file in order to develop and compile using the toolchain designed for the target device:

$ source /opt/welma/1.1.0/environment-setup*

Make the app

You are now ready to develop. Let's try to make and compile a simple C app. Copy this C code to a file myapp.c :

myapp.c
#include <stdio.h>
#include <unistd.h>

int main() {
    // Print "Hello, Welma !" every 3 seconds on stdout
    while(1) {
        printf("Hello, Welma !\n");
        fflush(stdout);
        sleep(3);
    }
    return 0;
}
And compile it for the target into a folder app: 
$ mkdir -p app/bin
$ ${CC} myapp.c -o app/bin/myapp

Auto launch the app

You may want your application to automatically start at boot, as user user (uid 2000). Welma uses systemd to start the application, so a service file is required. First, create the necessary directories:

mkdir -p app/lib/systemd/user \
         app/user/2000/systemd/user/default.target.wants

You need to create this file:

app/lib/systemd/user/myapp.service
[Unit]
Description = Launch demo application

[Service]
Type = exec
ExecStart = /app/bin/myapp

[Install]
WantedBy = default.target

You also need to create a link to this service file at a specific path formatted like this : 

$ ln -s app/lib/systemd/user/myapp.service \
        app/user/2000/systemd/user/default.target.wants/myapp.service

Create the update artifact

Use welma-update-gen to create your update artifact : 

$ welma-update-gen ./app
INFO: welma-update-gen: Configuration file loaded: default-image.imgconf
INFO: welma-update-gen: Signing verity image with key: /opt/welma/1.1.0/sysroots/x86_64-pokysdk-linux/usr/share/default-image.signkey
INFO: welma-update-gen: Signing swupdate artifact with key: /opt/welma/1.1.0/sysroots/x86_64-pokysdk-linux/usr/share/default-image.signkey
INFO: welma-update-gen: Created: appro-1.0.swu

Transfering and updating the app

You need to use either the -dev or -dbg welma image (with SSH access).

Link the host machine to the device via ethernet. Transfer the update artifact. Example : 

$ sudo ifconfig eth0 169.254.0.2 netmask 255.255.255.0 up
$ scp appro-1.0.swu root@169.254.0.1:/home/root/.

Now we can use updatectl (as root on the device) to install the app: 

# updatectl install /home/root/appro-1.0.swu
# reboot
After the reboot check and confirm the update (to make it persistent): 
# journalctl -f
Oct 28 10:50:07 sm2s-imx8plus-mbep5 myapp[588]: Hello, Welma !
Oct 28 10:50:10 sm2s-imx8plus-mbep5 myapp[588]: Hello, Welma !
Oct 28 10:50:13 sm2s-imx8plus-mbep5 myapp[588]: Hello, Welma !
...
# updatectl confirm

Conclusion

Congratulations! You've successfully performed an update using Welma!

And now you can iterate over short code-deploy-and-test cycles.