> -----Original Message-----
> > Where the beagle falls down on the Linux side of things, say compared to a
> Pi or a PC, is the video processing just isn't as good. And it shows even
> when
> just running normal Linux compared to normal Linux on a Pi.
> Well, I DO see a bit of sluggishness compared to a fast
> Intel CPU with graphics card, but it is
> completely tolerable, to me. And, LinuxCNC has been run on
> a Pi, but that port is apparently not
> ready for prime time, yet.
> > Where my LinuxCNC box falls apart is with the parallel port for stepping
> with very high latency issues and that one time warning when LinuxCNC
> starts up that I've basically got my motion parameters set too high for the
> system.
> There are desktop PCs that have horrible real time
> performance, for a variety of reasons, and some that have
> amazingly good RT latency. I make a line of 3 different
> motion controllers that use the parallel port as a
> communications
> path to an FPGA. On a variety of CPUs, the entire servo
> thread cycle takes from 100 - 200 us to service up to 4 axes,
> so a 1 KHz servo thread is totally reliable. With these
> units, there is NO base thread, essentially the base thread is
> moved out to the hardware. These devices support
> step/direction systems, and PWM and analog servo systems.
> I've been making these since 2002.
> > Might well be video drivers.
> There are clearly video drivers combined with certain video
> chips/cards that totally trash the realtime performance.
> Partly, that is do to trying to do software-generated
> stepping on a multi-purpose CPU. That's why I just don't
> recommend doing that.
>
> Jon
Hi Jon,
But that's my point. If I go through 4 different PCs from different sources
and each has latency issues at some point I'm going to say the heck with direct
control and let's use an Ethernet driven device. At this point the step
generation and closed loop has moved out of the PC hasn't it?
And BTW, these PCs are 1.8GHz and 2.4GHz. Given we were doing EMACs back in
the 90's with 33MHz PCs (maybe with Fedora? Don't remember) a fact of almost
100 times faster strikes me that these real time ports of Linux onto PCs isn't
what it's cracked up to be. Otherwise the suggestion that it must be the
other hardware seems iffy. And if the hardware cannot be controlled to that
extent because the drivers etc. are in the way then the solution is as the
subject line suggests, a separate open source hardware/software platform
running an RTOS that creates deterministic outputs. But that would also make
products like yours dated and that's not my intention.
I'd certainly be up for having someone modify my HAL and INI files so that I
can do the 50kHz step rates out the parallel port. After all WIN-XP and MACH3
can do it. But like I said, I have trouble understanding how a 2.4Ghz
machine can't do what was done with smaller micros running much slower.
John Dammeyer
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