Raspberry Pi 4

Hello Gene & all
Reporting back

Firstly by way of indicative comparison....
glxgears & browser circa 20mins duration
Ran latency-test period on my existing Pi2 4.4.4RT setup.
Came in at ~ 160

Re ran using rt-tests with:
cyclictest -n -p 90 -i 1000
Came in at 147

Similar enough to be indicative in that example at least. I will re test with the lcnc latency test in due course.

Tried the/your newer kernel on Pi4 with cmdline & config from your link.
Extraction seemed to run OK.
Hangs at boot ! Suspect it is something in your modified cmdline.txt ?
Edit
Prob not cmdline or config ? put stock ones back in with a kernel=kernel7i-rt.img
Still hangs at boot

Cheers
MrGreg

i disagree with the decision to run the pi headless. The net cable and an ssh connection is a huge video slowdown. With the video switched to GL using raspi-config, glxgears will run at full screen and over 50 fps!. Here its about 3.2 fps or a hair more over an ssh -Y connection. Its fine for writing code, but just doesn't cut it for running the code you just wrote, so I have a 21" high res 1920x1080 monitor plugged into the pi4's hdmi output0, and a usb2 cable plugged into the usb2 port, one of those with the 4 buttons on a hub on the far end of a 4 foot cable, hangs over the headstock with one or 2 dongles for wireless keyboards and mice, Since mine has to clear an overhead garage door, I've erected an overhead bar about 5 feet long, the left vertical carries the pi and its motor driver hardware on the rear of the post, a 650 WA UPS one the left face,. Another 2" post is duplicated a couple inches to the right of the right end of the bed, and a strip of dexeon connects the top of the posts, its carries a box with 2 SSR;s to control vfd and motor power from the F2 state, holds the vfd and has a 4000 lumen led lamp 4' long to put a good light on the bed. And my video on the monitor now that I've switched it to a pi4, is so close to real time that no lag can be detected. And my garage door clears it all by about 2".

IMNSHO you guys running it headless are totally throwing away your real time because the machine is fully capable of being several inches ahead of what you are seeing jerkily on the monitor. When dealing with potentially lethal power in a machine the size of this Sheldon, that lag can break tools, and injure or kill the operator.

Because I am building all this on that same pi, my usb3 ports have a couple SSD's plugged in via usb3-sata adaptors from startech, with the bigger 240G mounted via /etc/fstab as /media/pi/workspace, and the smaller is used as a backup of /boot, and has a 10G parition mounted in /etc/fstab as swap, and the swap-file turned off using the command you'll find in that fstab file, reducing the wear and tear on the micro-sd card. That swapfile is NOT big enough to build LinuxCNC as it may overrun the 100 megs it has while building the rs-274-d interpreter, I've had it happen due to OOM. The pi is also backed up nightly by several entries in the amanda disklist here on this machine. I do a backup of all 5 machines nightly, takes around an hour

Take care all.

MrGreg wrote: Hello Gene & all
Reporting back

Firstly by way of indicative comparison....
glxgears & browser circa 20mins duration
Ran latency-test period on my existing Pi2 4.4.4RT setup.
Came in at ~ 160

Re ran using rt-tests with:
cyclictest -n -p 90 -i 1000
Came in at 147

Similar enough to be indicative in that example at least. I will re test with the lcnc latency test in due course.

Tried the/your newer kernel on Pi4 with cmdline & config from your link.
Extraction seemed to run OK.
Hangs at boot ! Suspect it is something in your modified cmdline.txt ?
Edit
Prob not cmdline or config ? put stock ones back in with a kernel=kernel7i-rt.img
Still hangs at boot

Cheers
MrGreg

I don't think its hung, its probably fscking the u-sd card, which is feedbackless, and can take several minutes on a 64G sd card. If when its hung, there is activity on the pi's red led, thats what its doing.

Take care now.

MrGreg wrote: Hello Gene & all
Reporting back

Firstly by way of indicative comparison....
glxgears & browser circa 20mins duration
Ran latency-test period on my existing Pi2 4.4.4RT setup.
Came in at ~ 160

Re ran using rt-tests with:
cyclictest -n -p 90 -i 1000
Came in at 147

Similar enough to be indicative in that example at least. I will re test with the lcnc latency test in due course.

Tried the/your newer kernel on Pi4 with cmdline & config from your link.
Extraction seemed to run OK.
Hangs at boot ! Suspect it is something in your modified cmdline.txt ?
Edit
Prob not cmdline or config ? put stock ones back in with a kernel=kernel7i-rt.img
Still hangs at boot

Cheers
MrGreg

Talking to TomP just now we have another problem. In /boot/cmdline.txt the first option is "root PARTUUID, and one a different u-sd card it will be wrong, so it will likely hang there forever. I hope you saved the old one so you can get the proper # from it and put it into the cmdline.txt its using.

Also rename the new rt-kernel.img to kernel7l, the name it turns out is not speced, so bootcode.bin must be figuring it out on its own.

Hello

Well that's better, it's working
In fact I'm responding from it atm to give it a little different to do while the latency test is running.

So at the moment after about 10mins ish, I have, using:
glxgears at 1080p circa 60fps & active browser
rt-tests
sudo cyclictest -n -p 90 -i 1000
326uS

Started off initially at 96uS

Still a bit on the high side of expectations. Yes it depends on how you view the validity of the latency test. TBD / TBA ?
Lower (so far) by ~20% ish than the guysoft RT ( also 4.19.71 )
I'm rather seeing it as a comparative / indicative measure rather than an absolute specific directly related to lcnc.

Perhaps if someone could/would run the cyclic test from debian rt-tests on a more optimised stripped out setup that might yield a useful comparison for general information?

@ Gene

is there a suitable working linuxcnc deb in your collection to plonk in this so I can do a latency-test period on it?

Thanks for your everything

Edit & update
After circa 90mins of hard labour cyclictest reports 432uS latency. Pi4 shutting down and resuming normal duties for the rest of the evening. Exploratory to be continued....

Cheers
MrGreg

MrGreg wrote: Hello

Well that's better, it's working
In fact I'm responding from it atm to give it a little different to do while the latency test is running.

So at the moment after about 10mins ish, I have, using:
glxgears at 1080p circa 60fps & active browser
rt-tests
sudo cyclictest -n -p 90 -i 1000
326uS

Started off initially at 96uS

Thats awfull slow and its indicative of running chromium too.

Still a bit on the high side of expectations. Yes it depends on how you view the validity of the latency test. TBD / TBA ?
Lower (so far) by ~20% ish than the guysoft RT ( also 4.19.71 )
I'm rather seeing it as a comparative / indicative measure rather than an absolute specific directly related to lcnc.

Perhaps if someone could/would run the cyclic test from debian rt-tests on a more optimised stripped out setup that might yield a useful comparison for general information?

Where can I get it?

@ Gene

is there a suitable working linuxcnc deb in your collection to plonk in this so I can do a latency-test period on it?

Yes, all of those on my site were built from master 4 or 5 days ago. Should just put those in a separate dir, cd to it and "sudo dpkg -i *"

Thanks for your everything

Cheers
MrGreg