On 10/13/2016 8:01 PM, Chris Albertson wrote:
> For sophisticated motion control you really need both. (my internet is
> in robots, no as much CNC) One to run an OS and drive a user interface
> and screen and talk over a network and so on.  and a smaller processor
> to make I/O lines go up and down and drive motors and read encoders.
>  In LinuxCNC we sometimes have two processors a PC and a Mesa card.
> On an ARM based CNC, I think you'd see an "A" type perhaps it is a
> Raspberry Pi or perhaps it is an iPhone app.  Then you'd have "M"
> types physically driving the hardware.

This is what I like about the BeagleBone (the PRU substitutes for a
Cortex-M for hard-real-time bit-twiddling) and the Xilinx/Altera
SoC+FPGA combinations (where you can put the Mesa open-source VHDL
firmware in the FPGA).

It works particularly well if you drive the servo-thread timing via
interrupts from the hardware (with position captured by the hardware
when it fires the interrupt), thus side-stepping the relatively poor
ARM Cortex-A interrupt latency and jitter.

Charles Steinkuehler

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