> -----Original Message-----
> From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com]
> On Sun, 10 Mar 2019 11:57:53 -0500
> Jon Elson <el...@pico-systems.com> wrote:
>
> > On 03/10/2019 05:18 AM, Nicklas Karlsson wrote:
> > >> Hey Chris,
> > >>
> > >> AFAIK, the Pi has better HDMI support compared to the Beagle but then
> it was designed more for multimedia. The Beagle PRUs have the advantage
> that they have access to some of the Beagle Processor RAM. That gives
> them a bit of an advantage over the PI/32 bit hybrid using SPI.
> > >>
> > The PRUs are 200 MHz 32-bit RISC processors. There are 3
> > shared RAM data sections between the PRUs and the ARM. The
> > PRUs have a limited number of direct IO pads that bypass all
> > the ARM high-level I/O fabric, and so can be read/written at
> > the 5 ns rate of the PRU, which is a big plus for various
> > special bit-fiddling I/O tasks.
> >
> > Charles Steinkuehler wrote a general driver for Machinekit
> > that uses the PRU for step generation, PWM and encoder input.
>
> But why use a PRU then this kind of hardware is usually part of the micro
> controller and very cheap?
>
Jon,
You make a very good point. Why bother, with the new 32 bit controllers that
do so much even bother with the antiquated idea that the LinuxCNC PC should
close the loop on positioning. Running encoders from a servo motor back into
the PC to some sort of controller board that creates +/- 10V out is now not
really a good option.
Whether it's a PC with a plug in card running LinuxCNC or a BeagleBone Black
running MachineKit there's not much point.
Or is there?
For a lathe, spindle tracking in order to move the carriage and if also
tapering at the same time to track and move the cross slide does require
something tightly coupled.
So a Pi with an external STM32 may well send step/dir signals or SPI based
messages to the driver but tracking that spindle encoder for threading is a bit
more intensive.
John Dammeyer
http://www.autoartisans.com
> > Jon
> >
> >
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>
> --
> Nicklas Karlsson <nicklas.karlsso...@gmail.com>
>
>
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