Asrock Q1900B-ITX

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09 Apr 2019 18:52 #130570 by InMyDarkestHour
Replied by InMyDarkestHour on topic Asrock Q1900B-ITX

Edit: this was interesting.
Problem went away with this: disable parport in bios, boot (linux does not find parport). Reboot, set parport to manual, ECP1.7, 0x278, all irqs => works as it should.


I like your thinking

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10 Sep 2019 21:34 #144746 by ississ
Replied by ississ on topic Asrock Q1900B-ITX
Today I decided to test if he uspace version is suitable for paraller port usage too because of the good looking latency.
Installed using linuxcnc-stretch-uspace-amd64-r13.iso image.
Latency is quite good, ~4000 servo, ~13000 base (2x 8G samsung M471B1G73QH0-YK0 memory modules) with kernel command line "isolcpus=2,3 acpi_irq_nobalance noirqbalance"
Using irq affinity (all to cpu0) discussed elsewhere in forum the latency is a bit better but not significantly (only a few hundred after overnight test).

Latency stays at max ~5000 servo, ~15000 base when running overnight with 6 glxgears and youtube. Additional load with samba & file transfer does not make a difference.

But when starting linuxcnc I always get "Unexpected real time delay on task 0".

uname -a:
Linux sorvi 4.9.0-8-rt-amd64 #1 SMP PREEMPT RT Debian 4.9.110-3+deb9u6 (2018-10-08) x86_64 GNU/Linux

cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.9.0-8-rt-amd64 root=UUID=a07de53a-6564-44d7-b7c6-86c7ea742140 ro quiet isolcpus=2,3 acpi_irq_nobalance noirqbalance

Linuxcnc output on terminal:
Unexpected realtime delay on task 0
This Message will only display once per session.
Run the Latency Test and resolve before continuing.
Unexpected realtime delay on task 0
This Message will only display once per session.
Run the Latency Test and resolve before continuing.
Shutting down and cleaning up LinuxCNC...
task: 2050 cycles, min=0.000022, max=0.011068, avg=0.009994, 0 latency excursions (> 10x expected cycle time of 0.010000s)
Note: Using POSIX realtime

Linuxcnc 2.7.14 seems not to print anything to view with dmesg. No _print.txt or _debug.txt on home directory.

Any ideas why unexpected delay happens on startup with those latency numbers ?
Or something else that can cause unexpected delay ?

Maybe I should still stay with the old rtai version if this cannot be solved... odd because of the latency should not be an issue by looking at the numbers.
The following user(s) said Thank You: Richard J Kinch

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17 Sep 2019 12:41 #145384 by andypugh
Replied by andypugh on topic Asrock Q1900B-ITX
The uspace version of linuxcnc does not print to the kernel log.
To view the linuxcnc messages, start linuxcnc from the command line (just type "linuxcnc") and you should see the same output as RTAI versions print to dmesg.

It would be interesting to run a test where a step generator output is fed to an arduino or similar, with the time between steps logged by the arduino and process into 10 second bins and then sent back through USB for analysis.

Or simply run an actual stepper motor and see if the noise sounds very regular.

It is possible that this realtime delay message is spurious, or is a one-time thing at realtime startup.

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