Raspberry Pi 4

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15 Jul 2019 17:39 - 15 Jul 2019 20:54 #139473 by PCW
Replied by PCW on topic Raspberry Pi 4
Have you tried futzing with isolcpus?
EDIT: I had to set isolcpus=1,2,3 to get decent latency on my RPI3/LinuxCNC test machine:

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Last edit: 15 Jul 2019 20:54 by PCW.
The following user(s) said Thank You: tommylight

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15 Jul 2019 21:22 - 16 Jul 2019 04:13 #139504 by Hakan
Replied by Hakan on topic Raspberry Pi 4
No.

Well now I have. And it made all the difference in the world.
The following is with wlan0 disabled. Leaving wlan0 up and surfing at the same time
has a huge impact on the latency numbers.Surfing brings the max latency numbers
up a factor 5, around +- 100 us.




I can try some more tomorrow, it's getting late here.
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Last edit: 16 Jul 2019 04:13 by Hakan. Reason: Better graph and also with/without wlan0

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17 Jul 2019 14:09 #139695 by Hakan
Replied by Hakan on topic Raspberry Pi 4
I have tried some, but not yet been able to get a step going. I use the 7i76E mesa card via the ethernet port.
It is possible to get it going to the point where gmoccapy is displayed and reacts to Machine On/Off.
The 7i76E displays all the inputs and outputs as it scrolls by during startup.
But when I try to jog, there is a core dump by rtapi_app. No steps are taken.

I have noticed that "iptables -N hm2-eth-rules-output2 fails with "iptables: Operation not supported"
Obviously iptables is gone, say hello to nftables. Or
sudo update-alternatives --set iptables /usr/sbin/iptables-legacy
That helps for those messages.
Still, when I jog the tiniest distance I get
rtapi_app: caught signal 11 - dumping core
and then there is no reaction.

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17 Jul 2019 14:21 #139699 by andypugh
Replied by andypugh on topic Raspberry Pi 4
I guess you are building from source? Can you try this:

github.com/LinuxCNC/linuxcnc/blob/master/docs/rtfaults.txt

This will tell us where, and in which file, the core dump is happening.

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18 Jul 2019 10:49 #139774 by Hakan
Replied by Hakan on topic Raspberry Pi 4
I am unable to find that line in dmesg. I have never got any messages from linuxcnc in the system log file.
It is the rtapi_app that crashes. I have looked at it with strace and the last system command is "accept"
then crash. Intended to attach to rtapi_app with gdb, it should take me to the failing part upon crash.
But not succesful

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18 Jul 2019 11:10 #139779 by andypugh
Replied by andypugh on topic Raspberry Pi 4
gdb-debugging the realtime layer is tricky. It might be possible with preempt-rt but it is basically impossible with RTAI.

Did you make the makefile changes and recompile LinuxCNC? You won't see the ip without that.
I have only ever used that approach with RTAI, it is possible that is does not work with preempt-rt as the LinuxCNC modules are not kernel modules.

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18 Jul 2019 11:28 #139782 by andypugh
Replied by andypugh on topic Raspberry Pi 4
Another question: You said that you compiled the preempt-rt kernel? I did the same last night (4.19.58) and whilst it boots I seem to have lost the WiFi and Bluetooth drivers. Did you have this problem? Did you find a solution?

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18 Jul 2019 12:05 #139790 by tommylight
Replied by tommylight on topic Raspberry Pi 4
RPI3 with realtime kernel looses connectivity also, eth works.

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18 Jul 2019 12:11 #139791 by andypugh
Replied by andypugh on topic Raspberry Pi 4

tommylight wrote: RPI3 with realtime kernel looses connectivity also, eth works.


Is that with a self-compiled kernel, or a third-party released one?

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18 Jul 2019 13:05 #139798 by tommylight
Replied by tommylight on topic Raspberry Pi 4
With both, but i do not know the version i compiled then, i can get the verion i have now as it is the machinekit image, 2 years old.

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