RealTime-Kernel on RasPI2

[faehkerlohl]

So I've been tasked to provide and test various Linux-OS' with the addition of having a realtime kernel.
The first choice is obviously EmbeddedLinux with RT, but what you get is quite limited in functionality and because the RasPi2 will be used for "heavy" development, I'll need several options for remote-dev-tools.

Being an Arch-Acolyte for a long time and enjoying the ease of development using Arch (my Host runs Arch as well), I've been thinking to use LinuxArch|Arm on the RasPi2 - which is, again, quite easy to achieve.
The problem occurs with the realtime contraint: I don't have any idea how to patch the package linux-raspberrypi (4.1.17-3 as of writing this post) and if that even works because the raspi-kernel would differ in some points in the sources, preventing the patches to go through.

Does anyone have prior experience in trying to get the linux-kernel with RT on the RasPi2 or can give me pointers in how to proceed?
I've been looking into the other thread concerning RT-Kernel for Raspberry(1) but couldn't really follow the conversation and hoped that in the ~3years since then it got easier/feasible to accomplish.

[m16]

Hello,

I'd be interested in some pointers too.

mk

[venetanji]

Hi there! Also trying to figure this magic out.

At the moment the issue is that latest 4.1 rt patch (https://www.kernel.org/pub/linux/kernel/projects/rt/) is based on 4.1.15 but latest version of raspberrypi-linux is updated to 4.1.19 and the patch does not apply cleanly.

This guy built his own rt-kernel using 3.18.9: https://github.com/emlid/linux-rt-rpi

I just tested, patch for 4.4.3 applies ok to 4.4.y branch (https://github.com/raspberrypi/linux/tree/rpi-4.4.y)

I'll see if I can get it to run and let you guys know!

[venetanji]

Success!

Here's the PKGBUILD:

https://github.com/venetanji/linux-raspberrypi-rt

This is vanilla kernel (no BFQ, no aufs) from the raspberrypi/linux 4.4.y repo with latest rt patch.

Note that you may need to tweak your kernel config according to your hardware, here's a good starting point:

http://raspberrypi.stackexchange.com/qu ... ry-options

Removing unnecessary modules will speed up the compilation time.

Sorry but haven't fixed the checksums yet just run makepkg with --skipchecksums for now

If you want to recompile with different kernel config options run:

$this->bbcode_second_pass_code('', 'makepkg --skipchecksums --noprepare --noextract
')

to avoid recompiling the whole thing again.

[luoyi]

Hi, could you kind enough provide the compiled rt kernel arch linux arm package here ?

thank you very much .

[venetanji]

Here you go!

https://www.dropbox.com/s/i6q59d9vpnfiw ... ar.xz?dl=0
https://www.dropbox.com/s/7fsb6b47kxuac ... ar.xz?dl=0

I also updated the PKGBUILD so it should compile ok now and the checksums are updated.

https://github.com/venetanji/linux-raspberrypi-rt

Note that to get audio to work with 4.4.y you need to now add dtparam=audio=on to your config.txt, make sure it's there!

[luoyi]

which version of firmware do you use ? after upgrade to your firmware, my RPI2

1. can't get HDMI output
2. can't complete the reboot process .
3. can't find i2s audio card

but I can ssh into it.

[venetanji]

Some config options have changed in 4.4 kernel, you may need to add some lines to your /boot/config.txt

Check here for more info: https://www.raspberrypi.org/forums/view ... 9&start=25

output of dmesg can maybe help find out what's wrong, maybe paste it here I can have a look. I'm also getting an i2s audio card so definitely interested to make it work.

I'm running this on an rpi3 with no screen.

[luoyi]

sorry , long time not check this thread. I've rollbacked my kernel to the offical one. so doesn't have the dmesg now. maybe I'll have some time to check it again. and can you use your rt-kernel with the DAC board now ?