On 8/15/20 3:18 PM, John Dammeyer wrote:
When I installed the latest Linux CNC last fall onto several different Lenova
PCs they all failed the latency test for stepping past about 25kHz. Adding
external low profile video boards made it even worse. I bought 3 different
cards that fit those boxes.
The dual boot system ran WIN-XP and MACH3 with step rates up to 75kHz without
issues while LinuxCNC could not. The end result was to choose either an
Ethernet Smooth Stepper or MESA 7i92H. The MESA was cheaper so I went with
that.
As I understand it I'm not alone. The faster PCs if anything now more than
ever require an external step generator. In the Windows world MACH4 can't even
use the USB Smooth Stepper that MACH3 can on processor 10x faster than the
WIN-XP running my CNC router.
I think basically the fact is a general purpose computer board that runs Linux
still needs some sort of external step generator hardware interface. Either
through Ethernet, SPI, USB or multiplexed I/O.
I come across very few PC's that can't software step with LinuxCNC
<40Khz. Stay away from big brand name boxes with a crippled BIOS to make
support easier for their corporate clients.
Last year I even purchased my only Intel boards in the past 20 years.
https://www.amazon.com/Asus-Celeron-Mini-ITX-Motherboard-C8HM70-I/dp/B00APL76WO
$32ea with shipping used. Installed LCNC on stretch with preempt_rt andÂ
latency jitter was under 6us. Fast enough for gantry robots.
Anything AMD from 2005 -1018 by Asus or Gigabyte has onboard video and
low latency. i have several around here that we used for RTAI development.
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