LinuxCNC Versions ?

I see the current version of LinuxCNC is 2.6.12 AND 2.7.3. 2.7.3 was released Nov. 29, 2015 while 2.6.12 was released Jan 10, 2016. Why are there two current releases? What are the differences and which is suggested for a new install? Are both Debian based? Are there any speed differences for a stepper based system?

I downloaded 2.7.3 and installed from live CD figuring it was the latest. I installed over my 2.old LinuxCNC version. I was surprised to find Debian with a Xfce desktop. I like Debian but find it lagging a little on current software, which doesn't matter for this CNC application. Xfce, I believe, is a light weight desktop also very appropriate for a CNC machine. This should lower the overhead and allow the machine to run faster.

However, I think the max speeds before getting errors is lower using 2.7 than my prior version. I can't compare since I reinstalled 2.7 over 2.old. Is this possible? Would 2.6.12 possibly be any better? I could set up partitions for 2.6 as well as 2.7 and compare. But I thought it worth asking the experts for input before proceeding.

Please forgive my ignorance but I couldn't find any comparison between 2.6 and 2.7 beyond bug fixes. If this info exists please point me towards it.

Thank you for your help.

Hugh
Klamath Falls, OR, USA

The main difference between 2.6 and 2.7 is that 2.7 uses the new circular arc blending motion planner, that allows more than one line "look ahead". This allows much higher feed rates on code consisting of small line segments, for most machines. (typical of CAM generated 3-D tool paths.) 2.6 is the old parabolic blending limited in speed to what the machine's settings will allow it to come to a complete stop by the end of the next line (1 line look ahead).

Otherwise both are Debian Wheezy based, and are mostly the same.

Speed wise both should otherwise be the same (except when running short line segment code).

If you are having trouble achieving the same latency numbers with the new Wheezy installation, It should still be possible to upgrade an install from one of Linuxcnc's older Ubuntu 10.04 live CDs (with Linuxcnc 2.5 or so) to versions 2.6 or 2.7. But future versions Linuxcnc may not (I don't know what the future holds).

The minor difference in latencies from Ubuntu 10.04 to Wheezy shouldn't be enough to make a noticeable difference in performance, But it is possible you might need to back off the base thread in extreme situations to prevent alarm messages. You may want to fiddle with configurations and BIOS settings to try to improve latency to get them closer to your old results. (Maybe you were using isocpus on your old installation and you forgot to, or miss-configured it this time?)

Tod:

Thank you for the reply. The "new circular arc blending motion planner" as you describe it would sure be useful. I've done little profiling but will likely do more as time goes along. I'm using an Intel Dual-Core Atom Processor D525 in an ITX motherboard, not particularly fast but has worked well with LinuxCNC. Is there a document describing the BIOS tweeks which may help?

I brought the machine from the shop to my office where I have Internet. Ubuntu immediately started complaining about the out of date and unsupported OS. This convinced me it was time to upgrade rather than try to keep the Ubuntu install. So I installed LinuxCNC 2.7 and found the configuration files had changed. So there may be something amiss in the *.ini file also.

jepler:

Thank you for the response and explanation. It makes more sense now. So it was likely best I picked 2.7.3 since I was doing a fresh install. The trajectory planner and, obviously, better docs are useful. Also, not useful to drop back to 2.6.12.

I can't find the CD/DVD I used in 2013 to last install LinuxCNC, The newest version I've found in the archives is 2.0.3 (Ubuntu 6.06) which I'm sure is real old. I have 2.7.3 installed and working. I do think it's slower than the last unknown version, but I sure can't show this to be the case. It's workable and I have no complaints. When I have a chance I may try to tweek things further.

Thank you both for your help. I now know I haven't gone off the rails and am moving in the right direction.

Hugh
Klamath Falls, OR, USA

Mostly just make sure any and all power saving features in the bios are turned off. Also I think those boards usually benefit from isocpus=1 (or 0) sometimes one setting does better than the other. I've set up isocpus several times but I always have to google the instructions.

Good Luck

Did you backup and reuse your old configuration files? They should have worked fine (perhaps requiring minor modifications).
If you started over building new config files, are you sure you have it set up the same as before? (step timings, acceleration, max velocities, base thread...)

Todd wrote:

Mostly just make sure any and all power saving features in the bios are turned off. Also I think those boards usually benefit from isocpus=1 (or 0) sometimes one setting does better than the other. I've set up isocpus several times but I always have to google the instructions.

Todd: I looked at setting isolcpus but haven't tried it yet. Hopefully have time soon. Thanks for pointing me in this direction.

Todd wrote:

Did you backup and reuse your old configuration files? They should have worked fine (perhaps requiring minor modifications). If you started over building new config files, are you sure you have it set up the same as before? (step timings, acceleration, max velocities, base thread...)

I found I had 2.5.3 installed previously. When I moved those configuration files into 2.7.3 there were many complaints. My knowledge is limited so I started with a new stepper configuration rather than attempting to track down the errors. Today I compared the *.ini and *.hal files in detail. Many parameters had migrated, there were a few new declarations and file names had changed. But as near as I can tell they are the same. I did find the old configuration had "inverse" commands on the step parallel port lines:

setp parport.0.pin-03-out-invert 1
net Xstep => parport.0.pin-03-out
setp parport.0.pin-03-out-reset 1

rather than simply:

net Xstep => parport.0.pin-03-out

I found in my notes having to ask the stepper configuration GUI to invert these lines. I put in these commands and tried running the machine. It still works fine but not faster. Other than this the new configuration is the same as the old one, to the best of my knowledge.

I'll try setting isolcpus and look through the BIOS. But I am up and running, life is good. Now back to setting up a Sherline CNC lathe.

Thank you for the help, this is a great forum. I'll report back when I've tried the isolcpus and BIOS tweaks.

Hugh
Klamath Falls, OR, USA

Without knowing more about the specifics of your configuration, we can't say for sure what is limiting your top speed vs what you had before.

If you could post copies of your new and old ini and hal files (if you have the old ones). I'm sure we could pin down exactly what is going on. But even if you could only show us the new files and tell us what the old top speed was that would help.

If your old config was using reset to get 1 step/thread cycle, and your new config isn't, that could theoretically halve your potential top speed. (But this might not necessarily be the case.)

Todd wrote:

If you could post copies of your new and old ini and hal files (if you have the old ones). I'm sure we could pin down exactly what is going on. But even if you could only show us the new files and tell us what the old top speed was that would help.

Todd: I hate to ask for that much time, but I would certainly learn a lot having someone look at the configurations. I would appreciate the review if anyone has an interest.

The machine is a Bridgeport copy knee mill using very old NEMA 34 stepper motors. All steppers use 2:1 timing belts driving retrofit ball screws. The drivers are three Gecko G202 in an old PMDX-131 breakout board. The computer is an "Intel Atom Dual-Core D525/Intel NM10/DDR3/A&V&GbE/Mini-ITX Motherboard BOXD525MW" through Amazon. I think it is using 2GB memory. I'm using the on board parallel port. A PCI parallel port is installed but I haven't tried it with the new installation.

The prior LinuxCNC installation was 2.5.2 (not 2.5.3 as I stated earlier). The new installation is 2.7.3. The two attached text files, OLD.txt and NEW.txt, show the configuration files for each.

The NEW.txt file shows (I believe) the differences. The 2.5 configuration parameters are moved over as comments where they are different from the 2.7 ones. Parameters not found in 2.5 are indented for identification.

As seen, I needed to reduce the MAX_VELOCITY on each axis from 1.14 in/s (68 in/min) to 0.55 in/s (33 in/min). So not a small change but by a factor of 2. Something seems to be amiss. I'd like to verify the difference but the 2.5.2 version was overwritten and I don't have the install disk.

If I've missed some information please let me know and I'll try to supply it.

Thank you.

Hugh
Klamath Falls, OR, USA

I think it looks like Reset is probably why you can't go as fast as before. You haven't added the reset part of the parallel port driver to the base thread. You'll need to add these lines in the appropriate places in your hal file for the reset to work.
addf parport.0.reset base-thread
setp parport.0.reset-time 500

Alternatively you could just use your old config. The only change I see that you would need to make to use it with 2.7 would be comenting out or removing this line in the hal file.
loadrt probe_parport