On 01/24/2020 01:15 PM, John Dammeyer wrote:
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
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