G76 problem

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22 Dec 2022 19:41 #260097 by tommylight
Replied by tommylight on topic G76 problem
HP 8300 SFF are good, Dell 9020 tower and SFF are good but SFF does heat a lot and it can be kept under control by setting fans at full speed as there is no other setting in BIOS, some Fujitsu are also good.
Take this as a general reference, you may find the same model with diferent hardware, so that does not guearantie good results.
So far i went through 8 of HP8300, 7 of Dell 9020, all work good.
The Dell 9020 tower also has a parallel port and the latency is very usable for software stepping with RT-Preempt kernel, 10000 to 12000 steps per second.
Did not test with RTAI kernel, should do much faster software stepping.
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22 Dec 2022 20:05 #260099 by Ismacr63
Replied by Ismacr63 on topic G76 problem

Are the PCs you've been trying Laptops by any chance?

Laptop PCs are almost never good candidates for running real time applications. They usually have too many built in hardware intrups for power saving features that can't be overridden or turned off.

To be honest I haven't set up a "new" Linuxcnc PC for nearly a decade, and I can't make an experienced guess at a "good" current PC or motherboard. The last Linuxcnc machine I set up I used a used HP PC with an i5 CPU I claimed from our IT depts scrap pile. It gave OK, but not great latency. It was good enough for moderate software stepping with the Preempt-RT kernel.

It is a desktop PC. GA-EP31-DS3L motherboard (rev. 1.0) intel q8200 processor

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22 Dec 2022 20:07 #260100 by Ismacr63
Replied by Ismacr63 on topic G76 problem

HP 8300 SFF are good, Dell 9020 tower and SFF are good but SFF does heat a lot and it can be kept under control by setting fans at full speed as there is no other setting in BIOS, some Fujitsu are also good.
Take this as a general reference, you may find the same model with diferent hardware, so that does not guearantie good results.
So far i went through 8 of HP8300, 7 of Dell 9020, all work good.
The Dell 9020 tower also has a parallel port and the latency is very usable for software stepping with RT-Preempt kernel, 10000 to 12000 steps per second.
Did not test with RTAI kernel, should do much faster software stepping.

I'm looking at those PCs and the ones I see don't have a parallel port.

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22 Dec 2022 21:29 #260110 by Todd Zuercher
Replied by Todd Zuercher on topic G76 problem
For a software stepping machine, or with many older CPUs (such as your q8200) it is often better to use an RTAI version of Linux rather than Preempt-RT.

The Preempt-RT version is the one that is default for the current Linuxcnc installation. (because it is usually adequate for newer PCs and many Mesa hardware options require it.)

I'm not up to date on the latest installation methods/options. I'd start by consulting the documentation for the version of Linuxcnc you've installed for the best/simplest way to try to install the RTAI version to try to test it to see if the latency is better.
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22 Dec 2022 21:49 #260115 by Ismacr63
Replied by Ismacr63 on topic G76 problem
I was consulting the documentation and installed the RTAI kernel, unfortunately there is no improvement.
The truth is that I don't know what else to do, except change PCs, although it's also complicated because you buy a PC and then it doesn't have good latency.....

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22 Dec 2022 22:50 #260120 by tommylight
Replied by tommylight on topic G76 problem

I'm looking at those PCs and the ones I see don't have a parallel port.


Same here, i can not find them!
Only the big Dell's and some Fujitsu have parallel ports.
I have 2 of those Dell in the shop so i will check the exact models.
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23 Dec 2022 10:57 #260144 by andypugh
Replied by andypugh on topic G76 problem

The last Linuxcnc machine I set up I used a used HP PC with an i5 CPU I claimed from our IT depts scrap pile. It gave OK, but not great latency. 

Similarly, my development PC gives excellent ( < 1250ns ) latency but was just a random second-hand machine that I bought for other reasons (mainly being easy to move when I didn't want it in the way, it's an all-in-one, UK only,  education market PC with PCi, PCIe and parallel port)

Its an Intel Core i3-3220T CPU @ 2.80GHz but I have no reason to believe that any other PC with the same CPU would be anything like as good, as the motherboard and BIOS design plays a role. 

There is a not-all-that-useful thread here with lots of PCs and their latency scores. forum.linuxcnc.org/18-computer/39371-res...or-use-with-linuxcnc?
 
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04 Jan 2023 09:25 #260908 by Ismacr63
Replied by Ismacr63 on topic G76 problem
Well, in the end I bought a gigabyte ga-h61m-s2pv board, it has a latency that I think is acceptable. 


with 5 glxgears and open browser with youtube at 1080p it has 15000. 


only with the browser and youtube it has about 9000. 
It remains stable for about an hour. 

Now my question is how I have to configure the times and spaces. the drivers I have are t60 rtelligen and dm542y from stepperonline

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04 Jan 2023 12:15 #260921 by tommylight
Replied by tommylight on topic G76 problem
Start with the default 5000 for step timings, you can change those later.
To short timings cause skipped steps, so better be on the safe side.
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