# LinuxCNC 🚧

Controls CNC machines: milling machines, lathes, 3d printers, laser cutters, plasma cutters, robot arms, hexapods, and more. - LinuxCNC

see also

Setup

LinuxCNC 2.9.4

Live boot can be used to test latency.

Servo thread (1ms):  88k ns
Base thread (2.5µs): 87k ns

LinuxCNC on Linux Mint Debian Edition 6 

$ sudo apt update
$ sudo apt install linuxcnc-uspace

Then install RT kernel

$ sudo apt install -t bookworm-backports linux-image-rt-amd64

LinuxCNC on LinuxMint 22

# launch latency test
$ latency-test
Note: Using POSIX non-realtime   # <<== This is not good at all
## well all of this is probably bullshit => patching kernel is the most important
# make sure user is part of realtime & video group
$ sudo groupadd realtime              # create realtime group
$ sudo usermod -aG realtime $USER   # add yourself to groups
$ sudo usermod -aG video $USER      # add yourself to groups

# You must allow mlockall without limits.
$ sudo micro /etc/security/limits.d/realtime.conf
# add the following content
@realtime   -  rtprio     99
@realtime   -  memlock    unlimited
# save and reboot
# test
$ ulimit -r
99
$ ulimit -l
unlimited
  • add ui
    • add probe plugin

GUI

Configuration

Parallel port address

Parallel port is only seen by the kernel is pnpbios is active. (no pnpbios=0 options)

$ dmesg | grep parport
[ 11.551600] parport_pc 00:07: reported by Plug and Play ACPI
[ 11.551671] parport0: PC-style at 0x378 (0x778), irq 7, dma 3 [PCSPP,TRISTATE,COMPAT,ECP,DMA]
[ 11.648233] lp0: using parport0 (interrupt-driven).

Hardware Interface to CNC machine

  • USB to Parallel port converter - Will the USB to Parallel port converters work with LinuxCNC?
    • No, parallel converters will not work with LinuxCNC for step generation because they have large latencies to access the I/O pins.
    • A normal hardware parallel port will change it’s output pin state typically in less than 1 uSec from when the host CPU does the port write.
    • A USB parallel port may take from a few uSec to a few 10s of mS from the host write to the actual pins changing state. This random output timing makes evenly spaced step generation pretty much impossible.

PCIe LPT Card Status

Stepper Configuration

Latency-Test

The important number for software stepping is the max jitter of the base thread.

  • If your “Max Jitter” number is less than about 15-20 microseconds (15’000-20’000 nanoseconds), the computer should give very nice results with software stepping.
  • If the Max Jitter is more like 30-50 microseconds, you can still get good results, but your maximum step rate might be a little disappointing, especially if you use microstepping or have very fine pitch leadscrews.

  • If the numbers are 100 uS or more (100’000 nanoseconds), then the PC is not a good candidate for software stepping.

  • Some archived results of systems that works

Stress system

  • 3x glxgears (+ redim windows)
  • youtube video playing in 720p in firefox
  • stress with default cmdline / monitor temp
$ latency-test
or
$ latency-histogram # maybe more usefull

# charge the system
$ seq 3 | parallel -j 3 -n0 glxgears

Hardware

AMD A6-9500 config (2025)

Should be slightly better than previous config (+2%)

with kernel and default parameter

$ sudo micro /etc/default/grub
GRUB_CMDLINE_LINUX="... noapic acpi=off pnpbios=0 isolcpus=1"

Servo thread (1ms):  81k ns
Base thread (2.5µs):100k ns

Option to tune

# tuned with
GRUB_CMDLINE_LINUX="skew_tick=1 kthread_cpus=0 irqaffinity=0 rcu_nocb_poll rcu_nocbs=1 nohz=on nohz_full=1 isolcpus=1 intel_pstate=disable amd_pstate=disable idle=poll intel_idle.max_cstate=1 amd_idle.max_cstate=1 nowatchdog nosoftlockup quiet"
$ sudo update-grub

Servo thread (1ms):  60k ns
Base thread (2.5µs): 77k ns

# ++BIOS
# Cool"n'quiet disabled
# SVM          disabled (virtualisation)
# ACPI HPET    enabled

Note using nosmt is disabling proc 1 on this APU.

captured histogram

intel E2180 config (2019)

add Kernels options, with value found in LinuxCNC 2.7 wheezy image this reduced a lot jitter.

The Intel Core2Duo benefits greatly from the idle=poll parameter to the kernel, which disables the deep-sleep C-State of the CPU. The effect is equal to that of hogging one CPU core. RealTime

Option acpi=off prevent kernel to shutdown pc.

$ sudo xedit /etc/default/grub
GRUB_CMDLINE_LINUX="... noapic acpi=off pnpbios=0 isolcpus=1"

$ sudo update-grub
Max Jitter:
GRUB_CMDLINE_LINUX="... noapic acpi=off pnpbios=0 isolcpus=1 intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll"
Servo thread (1ms):  33k ns 62°C
Base thread (2.5µs): 58k ns

GRUB_CMDLINE_LINUX="... noapic acpi=off pnpbios=0 isolcpus=1"
Servo thread (1ms):  53k ns
Base thread (2.5µs): 38k ns

GRUB_CMDLINE_LINUX= default value
Servo thread (1ms):   45k ns
Base thread (2.5µs): 140k ns

## IRQ affinity
GRUB_CMDLINE_LINUX="... acpi=off pnpbios=0 isolcpus=1 intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll acpi_irq_nobalance noirqbalance"
Servo thread (1ms):  66k ns 62°C
Base thread (2.5µs): 43k ns

GRUB_CMDLINE_LINUX="... noapic acpi=off pnpbios=0 isolcpus=1 intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll acpi_irq_nobalance noirqbalance"
Servo thread (1ms):  25k 41k 22k 23k 35k 36k ns 62°C
Base thread (2.5µs): 49k 42k 43k 32k 31k 40k ns

BIOS/Hardware config

  • Disable onboard audio
  • Disable APM and ACPI bios settings Turn everything off that you can. Any power saving, anything related to suspending, cpu frequency scaling, etc.
    • Enabling ACPI could be the only way to get access to local APIC timer (much lower latency than PIC), as new mainboards do not come with legacy support of MPTABLEs.
    • Disable C1E power-saving feature in BIOS (could save about ~10-15ms on recent CPUs), this feature is activated regardless of ACPI or APM, thus needs to be disabled independently. See Wikipedia for more information on this.
    • If you have a CPU that is C-state capable, add the following line to the GRUB_CMDLINE_LINUX in /etc/default/grub: idle=poll and run update-grub. The idle=poll keeps the CPU in a loop checking to see if it is needed rather then it entering C1 waiting for a wakeup call. I’ve seen latencies go from 30-50us to around 4us (1-2us even) on 6 different systems. RealTime

Multicore

Interrupts (IRQ)

# wath irq pert type/cpy
$ watch -n1 -d cat /proc/interrupts

Linuxcnc HAL tutorial / github

  • #1: The Basics
    • wiring goes into .hal / setting goes into .ini
    • kinematics / motion module
    • net signal command / setp set parameter
  • #2: INI improvements
    • display axis,control / default.ngc / GCODE subroutine
    • halui - running command from the ui
    • axis HOME_LATCH_VEL (second search spead)
    • user command file => to customize axis (linuxcnc ui written in python) (eg: disable command ‘r’)
  • #4: PyVCP / gladeVCP - Virtual Control Panel that extend Axis GUI (button / slider / readout)

Jog-wheel

Wifi

FPGA

XFCE

LinuxCNC/Debian

Alternative

Written on October 29, 2020, Last update on September 28, 2024
cnc linux-system in-progress