Custom Mint-19.2 with Linuxcnc

Shouldn’t be a problem Clive.

I have tested the March 8th RTAI and Preempt versions on my home made 3 axis gantry router and various other PCs in my inventory. The RTAI version I actually tested homing and moving the machine but have not yet cut any material. My machine is controlled by a Gigabyte GA-E350N-WIN normally running Wheezy and pre-2.8 using two parallel BOBs. It is a very low powered PC and I'm concerned how well it may perform with the newer Linux version. I have been using LinuxCNC with this PC on a variety of machine configurations for several years starting with Ubuntu 10.4 and LinuxCNC 2.5. I thinking of getting a Dell Optiplex SFF as a replacement.

Some observations:

After homing the live machine I turned off the stepper power and ran the default linuxcnc file. Using the top command I monitored the axis CPU usage. For Wheezy it averaged about 75%, for Mint 19.2 it was about 50%. I don't know if the difference is real or a function of how the two systems measure usage. I also don't know at what point the CPU usage might be a problem.

Running a histogram on both versions gives very similar numbers with Mint slightly higher (~20 vs ~17ms). The difference could be due to Firefox vs. the Wheezy browser.

I also ran a histogram for both versions on a few other PCs with similar other activity. I made no effort to optimize anything. Here are the results in case anyone is interested.

Gigabyte GA-H61MA-D3V Intel G2020 CPU Preempt 31.8, 14.5, RTAI 9.1, 6.7

Intel D525MW RTAI 41.7, 34.6

ASRock J4105-ITX Preempt 60.6, 44.7 For some reason the RTAI version would not boot

HP laptop i5-3210 Preempt 92.4 73.6

Gigabyte GA-Z68X-UD3H-B3 Intel -5-2500K Preempt 222.1, 130.8

GA-E350N-WIN Preempt >216, >100

Thank you for all the work you have put into this alternative to the ancient Wheezy version.

John

Hi John,
Thanks for your feed back that was great.
With the versions you tried were they the MATE or XFCE versions ? The XFCE versions should produce better numbers due to XFCE being less resource hungry.
With the one board that would not boot with the RTAI ISO can you give a few details. Was it a complete refusal to boot from the media ?
Were you able to get to the boot loader screen ?
Did it go past the boot loader ?
Was it a case of not getting a login screen ? It was the last case mouse movement will bring the login screen up ?
Were you booting in “legacy mode” as opposed to UEFI ?
I only ask these questions as people can have different ideas of “not booting”.

I only tried the XFCE versions

Were you able to get to the boot loader screen ? Yes
Did it go past the boot loader ? No
I tried the normal boot and compatibility mode. Neither showed any response after selecting and entering a choice. Same for the check media choice. I had similar trouble when initially setting up this system. So I loaded the ISO on a different brand USB stick. Still no luck. I then tried an old Mushkin USB stick that has always worked on every other system. Still no luck but that stick has an activity LED which flashed for ~15-20 seconds after the boot choice. Unfortunately, I can't check for network connection as this system has my Ubiquiti Unifi network monitoring software when booted normally.

Were you booting in “legacy mode” as opposed to UEFI ? UEFI

I was really interested in checking the RTAI latency for this board as it is relatively affordable and has lots of connection options.

Interesting.
Would it be possible for you to download a std Mint 19.2 XFCE iso and try booting from that ?

Another thing to try is booting with by changing your UEFI to legacy or compatibility mode to see if that helps.
I have seen that behaviour before but only on an early intel iMac. But that has a 32 bit UEFI and needs the image modifying to boot a 64 bit kernel. I never looked that far into it.

I downloaded Mint 19.2 XFCE and was able to boot from USB flash. My normal OS on this system is Ubuntu 18.04 server which should be very similar to Mint 19.

A quick look at the ASRock forum revealed many people having trouble booting Linux flavors from USB. There was no pattern evident from the posts I read. Apparently there is no Legacy boot mode. It seems Intel removed that capability from the Gemini Lake series of CPUs.

I'm willing to try something else if you have any ideas. Meanwhile I'm going to try cutting something with my router using your RTAI version.

John