I7-3820 @ 4.3 GHz latency-test results.

As the DELL I poked at recently was not suitable for linuxcnc direct DP25 control I took a look at my main PC. Better, but nothing which would knock your socks off it seems.

Motherboard: Gigabyte X79-UP4
CPU: i7-3820 @4.3GHz
Comments: Live (3.4-9-rtai-686-pae), i7-3820@4.3GHz, 64GB RAM, SSD, GFX Cards: AMD 7950, running 5 screens. AMD 7870, AMD 6770. Hyperthreading enabled.
Max Interval (1.0 ms thread): 1016030
Max Jitter(ns) 1.0 ms thread: 17935
Max Interval (25 us thread): 48814
Max Jitter (25 us thread): 24529

Run-time of the test around hour, most of it idle plus a little shaking around flash heavy web page and watching a bit video.

~25 000 ns Jitter does not seem particularly bad. That is like 1/40 000 th of a second so I assume the stepper motor would run out of torque far before the jitter gets to be an issue?

I would disable hyperthreading and make sure _all_ power management options are disabled in the BIOS
This may improve you latency figures

PCW wrote:

I would disable hyperthreading and make sure _all_ power management options are disabled in the BIOS
This may improve you latency figures

Than you for the suggestion. I will keep it in mind for sure should the latency turn out to be of issue.

As this is my main PC which I am using for practically everything I'm not particularly keen on doing very heavy tweaks in bios specifically for linuxcnc usage. Although once the stuff is assembled and if the latency is issue I will be able to make a specific UEFI profile for it I guess if I end up using this for cnc control as well. I posted this mostly as an information as quickly googling did not give me any idea what to expect latency wise on this platform.

Or I might do a specific smallish machine extra for cnc with all the needed tweaks. For example, www.asrock.com/mb/AMD/AM1B-ITX/?cat=Specifications seems promising, but it seems no one has published so far any latency tests on AM1 platform at first glance. Or perhaps an Sempron on AM3, depends which platfrom is cheaper with a DB25 port when I get around to it. Atm I'm still doing sketches and figuring out what is possible and what is not so getting aroudn to actually doing something is a little bit off.

andypugh wrote:

Carniflex wrote:

Or I might do a specific smallish machine extra for cnc with all the needed tweaks. For example, www.asrock.com/mb/AMD/AM1B-ITX/?cat=Specifications seems promising,.

This one looks useful:
www.amazon.co.uk/Asrock-ASRock-Q1900DC-I...rboard/dp/B00KIJ8WDK

12V DC power jack and a parallel port header. Though reviews suggest that it is troublesome to run headless. (not an issue for a CNC controller)

Thank you. That seems indeed interesting. A bit expensive though? 90 £ is approx ~ 100 EUR ballpark or so?

Linuxcnc does not need particularly beefy CPU as far as I understand. So for roughly the same budget I might get, for example:
ASRock Socket AM1 AM1B-ITX - 27 EUR
CPU Sempron 2650 (1.45 GHz) - 32 EUR

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Total: 59 EUR

The AM1B-ITX (www.asrock.com/mb/AMD/AM1B-ITX/?cat=Specifications) has physical DB25 port (1 x Parallel Port (ECP/EPP support)) instead of the motherboard header that might save also a little? As far as CPU goes, though, The Sempron 2650 might not be particularly beefy. There is a comparison against that Intel Celeron (one tick lower dual core variant) - www.hardwaresecrets.com/article/Low-cost...on-J1800-Review/1884 Unfortunately I have not managed to find the linuxcnc latency test results for anything based on AM1 platform as far as I have seen so I have no clue if that one would actually make any sense against the Celeron board which seems to be doing more or less ok in linuxcnc latency tests. AMD has only a single channel memory for a start on top of lower clock rate. Although as far as linuxcnc latency goes, as far as I understand, a lot depends also on motherboard and bios implementation.

Another alternative might be a Sempron 140 or 145 on AM3 board. These are dualcore parts with one core disabled (although the few I have seen in person have been quite happy to OC up to ~3.5 GHz with the disabled core re-enabled). I have an impression that linuxcnc kind of likes single core chips.

andypugh wrote:

Carniflex wrote:

Total: 59 EUR

Don't forget the PSU. Your CNC cabinet probably already has 12V, so the 12V input motherboards are likely to be more convenient.

I plan to power the CNC with a ~500 W PC PSU which would provide me with approx 20A of +5V and approx 20A of +12V. It is going to be rather modest thing for a start with max 500x500 mm working area and somewhere around 100 mm for z-axis. The main idea is to get some experience on how things actually work before I decide if I want to pursue fancier CNC projects.