Raspberry Pi 4 RT Preempt Kernel

I've been trying to get the RT Preempt kernel going on my RPi4.

I followed this guide from our wiki:
I also tried the newer kernel but didn't find the fully preemptable option.
When I check the kernel after rebooting I get this:
When it's supposed to report back:
In the /boot directory I see 3 kernel images:
I'm kinda stuck... and need a kick start.

Thanks
JT

is the only difference I can see.

Ooh I see one more thing
www.raspberrypi.org/documentation/linux/kernel/building.md

The only two I have are:
JT

Browsing the repository for rpi-4.19.y-rt I see that fully preempt is selected and bcm2711_defconfig is in that one.

JT

Between the bootloader (preferably u-boot) and the preempt_rt kernel config one will want to turn off all power management, speed stepping, core clock governor etc etc so that the cpu cores stay at a constant clock rate and no clocks stop or slow down for power management for the memory, cpu cores, internal bus between the memory, cpu cores and the IO used for real time, etc etc. The features to adjust the above should not even be in the kernel unless they are required to lock them into their highest rates. Not doing so will just cause latency issues and less than optimum real time performance.

The stock preempt_rt kernel for the pi's I've seen don't do this.

Also check out QEMU to build arm64 kernels on your x86 PC to save hours or days of time
wiki.ubuntu.com/ARM64/QEMU
github.com/sakaki-/gentoo-on-rpi3-64bit/...QEMU-and-binfmt_misc

Yes, all tests I have made, and I think everyone here, is with rpi-4.19.y-rt. At least for the RPi4 that is the right one.
That needs to be updated in the wiki.
The build instructions for the RPi4 from the link I gave above is in principle OK. But with the rpi-4.19.y-rt version and to
double-check that full preempt is selected (it should). in the config.

Additionally,
- for acceptable latencies, add "isolcpus=1,2,3" to the line in /boot/cmdline.txt after you compile the kernel.
- to not have the system hibernate/suspend/whatever and bring down the ethernet interface after a while, do ( Ref:https://wiki.debian.org/Suspend )
That should make it possible to run 1 ms servo-thread with mesa ethernet-interfaced cards.
- to lower latency even further, bring down the wlan interface, but that is optional, I have it working fine here with the wlan0 active.

Bari, do you know any other settings that should be in place?

Bari wrote: Between the bootloader (preferably u-boot) and the preempt_rt kernel config one will want to turn off all power management, speed stepping, core clock governor etc etc so that the cpu cores stay at a constant clock rate and no clocks stop or slow down for power management for the memory, cpu cores, internal bus between the memory, cpu cores and the IO used for real time, etc etc. The features to adjust the above should not even be in the kernel unless they are required to lock them into their highest rates. Not doing so will just cause latency issues and less than optimum real time performance.

The stock preempt_rt kernel for the pi's I've seen don't do this.

I did turn off frequency scaling during the make menuconfig

Bari wrote: Also check out QEMU to build arm64 kernels on your x86 PC to save hours or days of time
wiki.ubuntu.com/ARM64/QEMU
github.com/sakaki-/gentoo-on-rpi3-64bit/...QEMU-and-binfmt_misc

I checked out those links but they are at a level way above me and didn't make much sense.

JT

It doesn't take that long to compile the kernel on the RPi4, a few hours at the most.

Took about 1.5 hours to compile the kernel on my RPi4. But doing it over SSH you just do other stuff while it runs.

BTW, I did get the preempt rt kernel up and going and I'm installing LinuxCNC now and used OpenBox as the window manager. Total time to do all will be 3 hours.

JT

I got as far as building LinuxCNC with debuild -uc -us but ran into an error...
So I made sure yapps2 was installed...
So I tested in python...
Then I checked to see if yapps was available.
Anyone have a suggestion?
JT