The weakest link

This is just an observation not targeting any of the comments in the forum.

Platform consensus seems to be the weakest link in this great software.

Not that there is not a solution but it is illusive. In contrast:

• Linux is powerful, precise and intolerant of misconfiguration, part of what makes it a business staple.
• CNC is likewise precise and gives superb results when the rules are followed.
• The drives must have everything just right, power supplies on the money, wiring just so.
• The application software expects proper configuration as well.

When we get to the pc platform it appears nebulous and consensus only gathers around illusive latency values which cannot be verified without investing time and money by chasing down a likely suspect, loading up test software and serially working though the issues, possibly with success. One guy gets great numbers for one set up, another struggles to get half that with the same hardware. Most of the pc or motherboards on the latency list are obsolete or have critics inside the forum. If one guys has an issue, others queue up to tell him they run the same box without problems. It reads like a sales pitch for Mach3.

I'll pay my dues and figure this out but I certainly understand the frustration on the forum.

Be patient with the next set of newbies who asks this same question again and again.

Actually I think people tend to make too much fuss about latency, making reducing the numbers a competitive sport and
spending days trying to shave off a few usecs here and there.

For software stepping systems (parallel port) the hosts latency may limit your maximum steprate somewhat
but unless you have a high performance drive system, you often run into stepmotor torque issues first.

There are many modern PCs that have quite adequate latency. The J1800,J1900 based CPUs have decent latency and are nice
fanless and fast systems. Some faster modern CPUs like the Intel G32XX with a decent H97 based motherboard have remarkably
low latency.

If you do have a higher performance system and move to hardware step generation or a servo system with feedback,
latency matters even less. With the right hardware, latencies is the 100's of uSec region are harmless,
so its actually not that easy to find a system the cannot be made to work
(laptops excluded, laptop CPUs often go on extended holidays when changing power modes)

PCW wrote:

For software stepping systems (parallel port) the hosts latency may limit your maximum steprate somewhat
but unless you have a high performance drive system, you often run into stepmotor torque issues first.

I appreciate your kindness to reply. So we can assume anything off Craigslist is ok? I am only half joking.

If you do have a higher performance system and move to hardware step generation or a servo system with feedback,
latency matters even less.

I appreciate your life's goal is not to write a novel inside of a cnc forum however to my original point, it is still a bit illusive. I have a suggestion, if this is allowed. To avoid serious geek overload, petition Linuxcnc to allow vendors to post on this forum, have a section where a vendor can post a latency spec'd laundry list, say a bill-o-materials for a minimal/mid/high range system (motherboard, cpu, add-on cards, case, power supply, memory, SSD, video, etc) and they can help new users purchase the right platform for vendor's proprietary hardware first time. They sell more, and the end users get more because they are zeroed in on the solution and not the theory. If there was one part number for everything... well I digress.

Users can do the same ("pimp my PC) and list the BOM for their setup as well. We will move from theory to practice .

To avoid serious geek overload, petition Linuxcnc to allow vendors to post on this forum, have a section where a vendor can post a latency spec'd laundry list

I think you will struggle to find a vendor interested in even selling a system with linux installed.

Likewise finding vendors even knowing about latency regards realtime kernels.
The only mentions of latency I have ever seen relate to network latency.

If someone was wanting to sell computers, tailored to use with Linuxcnc, components chosen for best latency etc, I cannot see why they would have any difficulty making their products known to the forum.

But if there is someone out there, they might have a niche market, albeit probably a 'high maintenence' one.

regards

blacksmith wrote:

I appreciate your kindness to reply. So we can assume anything off Craigslist is ok? I am only half joking.

The computer I bought on Craigslist does just fine. I believe there is a recommended system spec in the wiki somewhere, it lists a pentium 4 system. When I was looking in craigslist for an old PC to run linuxCNC I couldn't find many pentium 4 systems, a core2duo system was easier to find and cheaper or marginally more expensive in most cases. anything newer than a core2duo probably doesn't have an onboard parallel port. I haven't competed in any latency drag racing though maybe the computer I've been using without any problems isn't so great.

ArcEye wrote:

I think you will struggle to find a vendor interested in even selling a system with linux installed.

Pardon my naivete but are the vendors selling the Mesa, Pico, Mechatronics and the like disinterested in at least appearing to lower the barrier of entry for potential cash customers? If linuxcnc were even slightly cookie cutter at an entry level the userbase would explode and bring their money with them.

kornphlake79 wrote:

The computer I bought on Craigslist does just fine. I believe there is a recommended system spec in the wiki somewhere, it lists a pentium 4 system. When I was looking in craigslist for an old PC to run linuxCNC I couldn't find many pentium 4 systems, a core2duo system was easier to find and cheaper or marginally more expensive in most cases. anything newer than a core2duo probably doesn't have an onboard parallel port. I haven't competed in any latency drag racing though maybe the computer I've been using without any problems isn't so great.

The Intel naming convention requires flexibility; PCW mentioned the "Intel G32XX" which had a unit release in March of 2015. It's a Pentium.

New machines can still be had with parallel ports, (though some are well hidden). The brand new Lenovo i7 system bought for me at work for doing cad/cam and office work has a 26 pin header on the mother board for plugging in a parallel port, (but nothing provided external on the box). Parallel ports may be pretty uncommon on ready made systems, but they don't seem to be too hard to find on motherboards sold by them selves (which tend to have more bells and whistles than the bare bones stuff on the ready made shelf)

As was stated by PCW the J1800, J1900 motherboards with soc processors are out there with built in parallel ports. You can build a new PC using one of these MOBOs for less than $200.00. They are simple and have good latency.

Is it still necessary to have a parallel port, especially for a new system, as I see MESA have ethernet boards