ODroid as raplacement for Raspberry Pi

I basically just burned the official Armbian Bullseye image, downloaded kernel source with apt, applied Preempt-RT patches from kernel.org, and built. It did definitely work, but video performance was horrible. I've read a few forum comments saying that video performance was a problem until relatively recently. On the Ubuntu image (with no RT kernel) video looks good. So I'm thinking there are some patches that Ubuntu has that Bullseye doesn't.

I've just tried the same formula on the Ubuntu Jammy image but the kernel build dies due to what appears to be a script that is getting sourced actually being an executable. I'm thinking this is something caused by the Armbian build process because their official method of building the kernel is to cross compile. So I've got a cross compilation running right now with the RT patches.

> Try isolcpus=2,3 in grub

Unfortunately that performance is with that already applied. I'm about 90% sure there is an issue with the video support. No way should X be using > 50% cpu the way it was. I guess we'll see once this kernel build finishes.

> invalid nameserver in resolv.conf

You should be able to fix that sans text editor with `echo 'nameserver 8.8.8.8' > /etc/resolv.conf`

> linuxcnc-uspace package has now migrated to Ubuntu kinetic

Now that's very good news. Once RT patches are mainlined in the kernel our lives will be much easier.

The feedback on the Odroid forum is that their preempt_rt include the graphics stuff that the default debian one won't
They are waiting for the 6.2 kernel to be released to redo it.
I read somewhere that there is some mods to the linux kernel should make it to the 6.2 kernel specifically for the Odroid N2+

I tried the echo trick but it did not stick. I think now that there is some other fault preventing apt to work on the kernels I tried.
Ubuntu did not boot
Bullseye gets in an endless loop loading USB stuff, and never gets to a login screen
Only sid and bookworm got to a log on screen but neither could use apt to install anything.
 

> their preempt_rt include the graphics stuff that the default debian one won't

That tracks with my observation. I'm building tobetter's 5.15 RT kernel on their Ubuntu Server 2022.04 image right now. Hopefully that will go better.

I just saw some good news pop up on Hacker News. The Preempt-RT patches have been accepted into Ubuntu.

ubuntu.com/blog/real-time-ubuntu-is-now-generally-available

Apparently it's part of their insane Ubuntu Pro plan now, but there is a free version of that.

rodw wrote:

great!
So you built the patched kernel from the source at kernel.org?
I got a bit distracted and tried the imges here.
sd-card-images.johang.se/boards/odroid_n2.html
only Bookworm and sid work ...   kinda.

There is a bug which breaks network 

Talking about being waay off the mark!
The error reported by apt update was:
Release file for deb.debian/dists/bookworm/InRelease is not valid yet
This was caused because the system datw was set for 10 Jan, about 18 days behind!
So if you venture here, the following steps should sort it.
find your timezone here  en.wikipedia.org/wiki/List_of_tz_database_time_zones
thenI left it installing 1800 odd packages after I typed
We'll see if we can get a graphical environment before I go to bed....

rodw wrote:

great!
So you built the patched kernel from the source at kernel.org?
I got a bit distracted and tried the imges here.
sd-card-images.johang.se/boards/odroid_n2.html
only Bookworm and sid work ...   kinda.

There is a bug which breaks network

 
Talking about being waay off the mark!
The error reported by apt update was:
Release file for deb.debian/dists/bookworm/InRelease is not valid yet
This was caused because the system datw was set for 10 Jan, about 18 days behind!
So if you venture here, the following steps should sort it.
find your timezone here  en.wikipedia.org/wiki/List_of_tz_database_time_zones
then

I left it installing 1800 odd packages after I typed
We'll see if we can get a graphical environment before I go to bed....

> This was caused because the system datw was set for 10 Jan, about 18 days behind!

Ah, interesting. Good to know to look out for that.

> We'll see if we can get a graphical environment before I go to bed....

Good luck! For anyone else reading this, definitely don't `apt install ubuntu-desktop` when you want a desktop. It replaced by custom kernel.

My current status is that I've got tobetter's 5.10 RT kernel working on their Ubuntu 22.04 Server. I'm going to rebuild with their 5.15 RT kernel then test latency with latency-histogram. If results are positive I'm going to post my script in a new thread.

its not so much  system latency (which I would expect will be OK) but network latency. To test this you need a mesa network card, let it run linuxcnc  for a while and open another window and type halcmd show param hm2*tmax*
The read and writes are the ones to look at. The results are in timer ticks so if you have a 3.4 gHz CPU, divide by 3400 to get usec (1000 usecs per servo-thread cycle.)

Hmm, if you follow my footsteps. be sure to expand the partition first thing. I ran out of disk space!
BAck to square 1, writing image to HDD cos apt got broken...
I think it is only 2 gB or so by default...

Thanks, I'll try that out.

I am however interested in system latency too. I have a crazy idea of using one of these board computers to do software stepping. I know it's unlikely to work given latency requirements, but at least I'll have fun finding out for sure.