About unexpected realtime delay ...

Hi!

Maaybe check this:
forum.linuxcnc.org/9-installing-linuxcnc...or-new-rtai-packages

Gave me great latency values!

Further reading for 2.7 rtai:
forum.linuxcnc.org/18-computer/25927-red...lticore-pc-s-success
In combination With setting max cstates
Gave me latencies below 10.000ns

On the 2.8 with 5.2rtai (first link) other tips made it worse. Will investigate further...

One thing is for sure: rtai will give you much better results!


Regards
Domca
I

if you are on softwarestepping 35000 is well good to go
what kind of interface and drivers are you using

pl7i92 wrote:

if you are on softwarestepping 35000 is well good to go
...

However, this motherboard can do 5000nS, so, why not to squeeze that:)

tommylight wrote:

Oh well, if you are using almost any BOB, those short pulses will disappear somewhere on their way to the drives, and most cheap drives do not even work with anything under 10.000uS.
It is very nice for directly reading encoders!

You are right, but do not we talk about latency test and not pulse width?

P.S. I personally use cheap, china made, 2x BOBs and cheap 5x DM542 drivers, and they are okay at 32kHz pulses rate (steplen 1, stepspace 0, dirhold 11000, dirsetup 11000, base _period 31250)

pl7i92 wrote:

if you are on softwarestepping 35000 is well good to go
what kind of interface and drivers are you using

I am currently finishing my Sorotex AL-Line. I am using their parallel port BOB on an old Athlon 64 dual core.
The CNC in X, Y has spindles with 10mm/turn and is suggested to run with 6m/min and 3200 microsteps.

Looks like with my setup I can run it with this specs.

l2-max wrote:

I do not think my tweaks will help you much as you and I running different Debian releases.

Initially, latency test on this mother board shown 16uS with official RTAI 2.7.14 ISO image. Then I switched to 2.8 master branch. Latency remain exactly the same as with official release despite kernel changed to preempt-rt. If you cannot reach such latency with clean 2.7.14 RTAI on the motherboard then I am not sure my BIOS setup will help you much.

Sorry, I do not have LinuxCNC machine by hand thus, what I recall, I disabled "INTEL speed step" (-3uS) to run processor at constant speed and may be, not sure disabled virtualization (not sure it had some impact on latency). I also isolated CPU on 2 cores only (that tweak helped a lot -8uS) and latency dropped down to 5uS.

That is it, from what I remember had noticeable impact on latency. Try booting from 2.7.14 RTAI flash drive and run latency test to see if it will be different from what you have now.

I briefly installed RTIA at first and I had very low latency numbers as well. Many around 16uS like you.
But I have an ethernet Mesa 7i92 card so I had to switch to PREEMP. With the official image I was getting about 50-70uS, but had ramdom spikes up to several seconds. Tried lots of tweaks that lowered latency a bit but didn't get rid of the spikes.
Maybe it would have helped if SMICTRL had worked at all for me.
Tried Mint and Lubuntu as well, but it didn't help.
Now I'm back on Debian 9, latest version, with pre-compiled PREEMT from rep. I don't get those 2-3s spikes any more. Now they only reach maybe 120uS.
But since I'm using a Mesa card I guess my numbers are ok.

DomCa wrote:

Hi!

Maaybe check this:
forum.linuxcnc.org/9-installing-linuxcnc...or-new-rtai-packages

Gave me great latency values!

Further reading for 2.7 rtai:
forum.linuxcnc.org/18-computer/25927-red...lticore-pc-s-success
In combination With setting max cstates
Gave me latencies below 10.000ns

On the 2.8 with 5.2rtai (first link) other tips made it worse. Will investigate further...

One thing is for sure: rtai will give you much better results!


Regards
Domca
I

Says it's only for AMD CPUs? But looks interesting!
Does Mesa ethernet cards work?

pl7i92 wrote:

if you are on softwarestepping 35000 is well good to go
what kind of interface and drivers are you using

Me or TS?
Using Mesa 7i92, so I guess my numbers are good enough.
Leadshine MX4660 driver.