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

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.

Am I right that we are talking about results tested on rtai kernel? On rt-preempt kernel I have huge worse results comparing to the rtai. Main problem with rtai debian wheezy is unsupported graphics on this motherboard. The resolution and rendering is bad enough.

I used the old rtai version with this board and it worked well.
The problem was that I wanted a newer os version and couldn't get it to work correctly. Latency test was ok but starting linuxcnc always resulted in that unexpected delay.
I solved the situation with another board (Portwell WADE 8012) wchich works well (I have 1 with mesa pci, 2 with mesa eth).

Is there a way to not rely on motherboard latency capabilities and use linuxcnc as software to control some independent hardware module which will generate steps?

On an ASRock J3355B-ITX (celeron 2 cores) , I just add a MESA 6i25 to the config to solve latency problems and to remove stepping generation form the motherboard cpu. I have keep the same pinout as the parport.
the 6i25 was available form eusurplus fiew weeks ago. A little expensive with vat and shiping.

macsddau@linuxcnc wrote:

On an ASRock J3355B-ITX (celeron 2 cores) , I just add a MESA 6i25 to the config to solve latency problems and to remove stepping generation form the motherboard cpu. I have keep the same pinout as the parport.
the 6i25 was available form eusurplus fiew weeks ago. A little expensive with vat and shiping.
 

And what BASE_PERIOD became after installing this MESA 6i25 ?