7I76e sample configuration

freeby.mesanet.com/7i76es1.zip

This is a simple sample configuration file set for the 7I76e that illustrates two techniques for limiting the effect of
host communication jitter on step generation accuracy. This is especially important for Ethernet cards running under
Preemt-RT which has higher jitter than RTAI or Xenomai.

The first technique is to not use the built in position mode stepgenerator feedback code in the driver but rather use a PID loop
in the hal file like a velocity mode servo. This allows for finer tuning the feedback loop to be less susceptible to host jitter. The main
PID parameter that is useful for this is the maxerror parameter. When moving at high speeds, a delay in reading the stepgens position
register (caused real time jitter) will look like a large position error and the PID will multiply this error by the P gain and make a large bogus
correction in the stepgens velocity. By limiting the error, the magnitude of these corrections can be likewise limited.

The second technique relies on a new firmware module, the DPLL. The DPLL (Digital Phase Locked Loop) synchronizes to linuxcncs servo thread read access and acts a bit like a flywheel. It allows sampling of inputs (like the stepgen position register) at a more constant frequency
than linuxcncs sampling which has host dependent jitter. The DPLL can typically reduce the input sampling jitter magnitude by a factor of 10-20,
allowing high performance step generation even with host jitter in the 100's of usec region

To use the DPLL you may need to update the firmware, as this feature was added relatively recently. Firmware that contains the DPLL has a "D"
in the filename (XXXXD.bit)

Do you have an XML or PIN file for the 7i76e?
A printout of all the pins would be helpful too.

Thanks Chris M

Here is a pinout for the 7i76e_7i76x1D config (that the 7I76E ships with)

PCW,

Once again you are at the forefront of the Help Brigade. Thank you for your time and willingness to help the rest of us!

I'm attempting to set up a WorkBee CNC router using a dedicated Linux Dell Workstation 490 (Dual X5355 Quad Core @ 2.66 GHz, 16 GB RAM, 750 MB SSD). Yeah, I know...it's like mouse hunting with an elephant gun, but it was a gift so the price was right.I'm not certain at the moment of the exact video card, but I do know that it's not a screamer and does not utilize proprietary drivers...at least that's what I was told. The computer feeds a Mesa 5i25 FGPA which in turn drives a Gecko 540.

I've built the machine from a LCNC Live CD and run the updates as indicated. The LCNC demo runs fine on the machine using Axis. I have not yet attempted to run PNCcnf.

My stress test involved running 3 copies of glxgears, playing audio, and running Unigine simultaneously for two hours. The result was a Base Jitter north of 150K ns! I am unsure of what to do next.

My questions are: 1) Would DPLL be a solution, and if so can you point me to a resource on how to implement it, and 2) I've read that isolating/dedicating processor cores can help lower jitter. Is this something I should be investigating?

Any other suggestions would, of course, be greatly appreciated.

Thank you again for your time and patience.

Leonard M.

1. Try running the latency test with only the servo thread (since the base thread will not be used in the actual working configuration)
2. Make sure all power management (C states above C1, any speed changing options)
are disabled in the BIOS
3. You can try isocpus

100 usec is probably OK without a DPLL

Thank you for the quick reply.

Translation please: "...C states above C1, any speed changing options". Are these what we're talking about: Core Performance Boost, Turbo CPB, Cool&Quiet, SVM Mode, C6 Mode, APM? If so, how do I check to see that they're disabled? Through BIOS, or in grub/menu.lst? Sorry, but ignoranceShowingNow = ON.

Also, re: isocpus...Do I need to isolate cores on both processors or just Processor 0?

Good link in LCNC Wiki on isolcpus: The Isolcpus Boot Parameter And GRUB2

Thanks, again!

Leonard