RPI4 Raspbian 64 bit & LinuxCNC

works on 8gb, the 5.10 atleast , but im getting constant low voltage warnings which are (presumable) causing intense latency spikes, works pretty good on cm4 2gb

i think there are too many closely related threads here

and this hread is about rpi 64 bit so i post again...

elovalvo's 64bit runs well on pi4 4g
aarch64 5.4.61-rt37-v8+ 2.8.1
30.2 max base latency after 14 hrs
latency-histogram --base 80000 --servo 1000000
with 4 glxgears
hth
tomp

Another 14 hr run gave me 25.8 max base latency.
I use
latency-histogram --base 80000 --servo 1000000
with boot params of
isolcpus=1,2,3 idle=poll
and disable the screen blanking & screensaver

I dont know why 80 uS base period is such a sweet spot,
but 50,60,70,90 and 100uS were all tested. ( many tmes on may pi's )
and all (non-80) were not as good.
Why is 80 'sweet'?

I did get pretty good resuts from 50uS base period,
seeing 34uS latency after just a couple hours.

I was ready to discard the 50uS as a possible based thread period,
but it leaves 16 uS.

I say this ("leaves 16uS") because I believe the period - latency = reliable time available.
Is that true?

Then...
how good is 16uS as a time to get everything done?

When people say that 20uS latency is good in the context of a 50uS thread period,
are they implying they need 30uS to accomplish all tasks?

Is there a profiler that can determine how much of the period is used/unused?

thx
TomP
tjtr33

Thx Andy
also
i ran a 50uS base thread ( still running)
and have max latency 28.7
i did change the environment in that i setup Samco's suggested ntp fix.
lateny-histogram --base 50000 --servo 1000000, with 4 glxgears
isolcpus=1,2,3 idle=poll
over 17hrs now
tjtr33

A total newbie I am trying to install this on a new PI 4b 8G
I get to here and it cannot find this file
git clone github.com/LinuxCNC/linuxcnc.git emc

Then I am done.
What am I doing wrong? any help is greatly appreciated

Thanks Andy,
I am following the procedure at the top of this string.
Your command worked but stopped on the next command after that. Below is the whats left for me to follow.
I am totally new to both LinuxCNC and Rpi4 but I was able to install the 64bit OS and the Real time Kernel rt64-kernel.tgz.
I am stuck on building LinuxCNC for PRI4 64 bit and installing it.
Below is where it all ended for me.


git clone github.com/LinuxCNC/linuxcnc.git emc
cd emc

debian/configure uspace
dpkg-checkbuilddeps

debuild -uc -us
cd ..

The .debs file can be also download from this link:
LinuxCNC_64bit.zip

Installing LinuxCNC:

cd ~/
wget ftp.it.debian.org/debian/pool/main/p/pyg...2_2.10.1-3_arm64.deb
sudo dpkg -i python-gtksourceview2_2.10.1-3_arm64.deb
sudo apt --fix-broken install

sudo gdebi linuxcnc-uspace_2.9.0~pre0_arm64.deb
sudo gdebi linuxcnc-uspace-dev_2.9.0~pre0_arm64.deb
sudo gdebi linuxcnc-doc-en_2.9.0~pre0_all.deb

If you followed Andy's command, the following command must move you to a new directory called 'linuxcnc-dev'

So the 'cd emc' command becomes 'cd linuxcnc-dev'

Also be careful that the command
wget ftp.it.debian.org/debian/pool/main/p/pyg...2_2.10.1-3_arm64.deb

will have to be fully extended to

wget ftp.it.debian.org/debian/pool/main/p/python-gtksourceview2_2.10.1-3_arm64.deb

Thanks that worked but now I am getting this error

dpkg-checkbuilddeps
dpkg-checkbuilddeps: error: Unmet build dependencies: debhelper (>= 6) libudev-dev tcl8.6-dev tk8.6-dev libreadline-gplv2-dev asciidoc (>= 8.5) dblatex (>= 0.2.12) docbook-xsl dvipng ghostscript graphviz groff imagemagick inkscape python-lxml source-highlight w3c-linkchecker xsltproc texlive-extra-utils texlive-font-utils texlive-fonts-recommended asciidoc-dblatex libxmu-dev libglu1-mesa-dev libgl1-mesa-dev | libgl1-mesa-swx11-dev libgtk2.0-dev intltool autoconf libboost-python-dev netcat libtirpc-dev

I am assuming that these did not load correctly up in the build Phase I did get some files not found notes but no errors that I can remember