good small cheap compatible computer?

Hello,

I just assembled a Q1900M small PC for the sole purpose of running LinuxCNC.

So the live image installed fine but USB won't work at first, luckily I still had a PS2 keyboard lying around and after an apt update and upgrade, the USB now works perfectly.

Fine small PC for 200$ all included... BUT... I have Max Jitter of 25000 for 1ms and of 24000 for 25us...

I purchased this PC to replace an old Athlon X2 Based machine and I do not get much better results in Latency... What could be wrong ?

Thanks

Do you have all power management turned off in the BIOs?

I have a J1800 (Gigabyte GA-J1800N-D2H) and it gets latencies (as reported by the latency test program)
in the 11 usec region

Thanks, disabled power management, speed step and pretty much every I could in the bios.
Also disabled audio and found an old Geforce 6600 fanless to put in the PC...

Now 7.5 usec for the 1ms servo thread and 17.5 usec for the 25 us base thread...

Not perfect but better, did you keep the onboard video ?

some Details :
Intel Speedstep : Disabled
CPU C States support : C7
Ehanced Halt state (C1E) : Disabled
No Execute Mem protection : enabled
Intel Virtualization : disabled

IGPU : Disabled
Onboard HD audio : Disabled
Deep S5 : Disabled
PCIE1 Link speed : auto

Yes thats using the onboard video

Can you disable any C state switching?

I would not disable the GPU

I dont think the sound makes much difference (its enabled on mine)

The Jitter depends much on the version of Linux. With ubunto (10...) I' m in the range of 4000, but with debian (12...) its much slower with 7000 and the slowest is with the RT-preempt, than its some 30.000.

Now C state switching is also disabled but still I think the results are quite poor for a recent computer

I get 24874 ns max jitter for the base thread... It is about 8000 until I start 3 or 4 glxgears ... Maybe I push it a bit too far ?

Debian Wheezy Xfce / Kernel 3.4-9-rtai-686-pae

So my conf is Q1900M + Gefore 6600 gfx card :
Intel Speedstep : Disabled
CPU C States support : Disabled
Ehanced Halt state (C1E) : Disabled
No Execute Mem protection : enabled
Intel Virtualization : disabled

IGPU : Disabled
Onboard HD audio : Disabled
Deep S5 : Disabled
PCIE1 Link speed : auto

Have you tried with the on card GPU (IGPU enabled)
Like I said I get around 11 usec with a GIgabyte J1800D2H using the on card video

PCW wrote:

Have you tried with the on card GPU (IGPU enabled)
Like I said I get around 11 usec with a GIgabyte J1800D2H using the on card video

Tried it again and now also 11 usec exactly as you. Thanks.

Hello,

For those reading this thread I would like to warn that I am having issues with the mainboard and the parallel port of the Q1900M
The thread is HERE

I doubt that your troubles are related to the parallel port (unless the port is actually bad)
(the Q1900 uses the same ITE chipset that many motherboards with parallel ports use)

More likely there is some marginal level issue with the breakout board.
You can trace this pretty easily by measuring the voltage at the parallel port pin (pin 12 for example)
in both switch states and see if both levels are valid signal levels (0.4V or less for '0', 2.4V or greater for '1')

Inputs that stick in one state are symptomatic of marginal levels driving a input with hysteresis
( and many parallel port inputs have hysteresis for improved noise immunity )