working w Yocto

[amamory]

dear Kevin,

I am planning to integrate one of your preempt_rt kernel releases w Yocto, to have a more updated rt kernel version than the 4.19 version provided by meta-raspberrypi. I have seen that you started some discussion here, which i think it would be a 1st step before updating meta-raspberrypi itself.

Right now i am in planning phase, trying to figure out the macro steps required to reach that goal. Currently i see two possible approaches:

• change meta-raspberrypi`s linux-raspberrypi.inc and its related recipes to point to your github repos
• skip meta-raspberrypi all together and create a new image definition pointing to your repos

If you have interest in the subject, i'd love to hear your ideas and suggestions.

Cheers!

[kdoren]

@amamory I'm not really familiar with Yocto or meta-raspberrypi. I build boot images for Raspberry Pi using my "jambox" fork of pi-gen:
https://github.com/kdoren/jambox-pi-gen

jambox-pi-gen installs the deb packages from my jambox-project apt repo (info here):
https://github.com/kdoren/jambox-debs
using packages listed here:
https://github.com/kdoren/jambox-pi-gen/blob/jambox/stage3/05-install-rt-kernel/00-packages

I have a script that installs multiple kernels and selects one as default ([all] property). The script that does the install is here:
https://github.com/kdoren/jambox-pi-gen/blob/jambox/stage3/05-install-rt-kernel/01-run.sh

My application uses USB audio. For performance, USB on Raspberry Pi foundation kernel uses FIQ, which does not play nice with PREEMPT_RT, and requires the use of spin-locks (those come in the extra rpi-specific patch set). In my testing the low-latency -llat kernel performs slightly better than PREEMPT_RT in terms of overall jitter that the application sees. So I use the 32-bit low-latency -llat (PREEMPT) 5.10 kernel as the default. 5.15 is installed but is not the default because it's not released yet for Raspberry Pi.

FYI the standard linux kernel (used by i.e. Ubuntu), when built for Raspberry Pi, does not use FIQ and spin-locks. But it also does not support HAT cards and some other Raspberry Pi features. I don't know how it performs for either USB, or PREEMPT_RT, I have never tested it.

What is your application?

[amamory]

@kdoren I am planning to use it for robotics application, so audio, video processing, gui, etc ... these things will be out of the image.

[matthiasklein]

@amamory I think it's a good idea to make this kernel available in the Yocto context. I don't need it at the moment, but I am available for testing.

[amamory]

@kdoren @matthiasklein
Thanks for the feedback ... I was at this moment evaluating the potential interest in this idea. Please, let me know if you have suggestions on how to approach the problem.

At this moment, I think I will:

• get the latest version of meta-raspberry
• reuse the existing kernel recipes and try to tweak it as little as possible to include the kdoren's latest rt branch.

I'll try to fit this task along this week. I'll let you know about the results.

[amamory]

Reporting some partial results here. In summary, I managed to make Yocto (dunfell) to fetch and compile @kdoren ' s kernel rpi-5.15.12-rt integrated w meta-raspberrypi. All you have to do is:

• to define these files:

  • linux-raspberrypi-rt_5.15%.bb;
  • linux-raspberrypi_5.15%.inc;
  • defconfig_5.15-rt;
  • config_5.15-rt.cfg.

• Define these options so that the default kernel is replaced by the newer one:

  • PREFERRED_PROVIDER_virtual/kernel = "linux-raspberrypi-rt"
  • PREFERRED_VERSION_linux-raspberrypi-rt="5.15.%"

The compilation and image build was successful ... but i am still debugging the actual execution in a RPI3.

If there is someone out there w more experience w Yocto, it would be nice to share some ideas. Please take a look at this repo to see the overall results achieved so far.

Cheers!

[mebel-christ]

@amamory
Lately I have been experimenting with the RT patch and linux-raspberrypi in combination with Yocto as well. Would be glad to join your effort. I have a fair amount of experience with Yocto so I will have a look at your repo!

[amamory]

@micaeb Great to hear that. Please let me know any feedback related to that repo.
Meanwhile, would you have some similar work (i.e. rt related) available ?

[mebel-christ]

@amamory I have nothing publicly available yet. I looked over your recipes and how you structured everything and might have some ideas for improvements even so I think they are minor. But I guess this goes beyond the work and interests of @kdoren . Should I open up a discussion in your repo to further go into detail on that?

[amamory]

Done ! You can find this new discussion here.