Search Results (Searched for: raspberry pi 3)
- Onat
- Onat
20 Jan 2025 14:16
Replied by Onat on topic LinuxCNC on Raspberry Pi 5
LinuxCNC on Raspberry Pi 5
Category: Installing LinuxCNC
- TOLP2
- TOLP2
18 Jan 2025 11:02
RPi + Sipeed Tang Nano 20 k: new breakout board for LitexCNC was created by TOLP2
RPi + Sipeed Tang Nano 20 k: new breakout board for LitexCNC
Category: Driver Boards
With the 5A-75B and 5A-75E we have a low cost way of creating a driver board for Linux-CNC. Based on the work of Romanetz, the project
LiteX-CNC
was started, providing a easy customizable firmware and driver to use these boards. The down-side however is that these boards require some soldering work to be done to accept inputs; I've messed up some boards in the process....
Therefore, Litex-CNC is going to be expanded to accept more FPGA's, starting with the Sipeed Tang Nano 20k. Compared with the 5A-75B it has less outputs (28 compared to 48 for the 5A-75B), but this is still enough for a simple 3 axis machine. The big advantage is that no SMT soldering skills are required to get this board up and running.
For the Raspberry-Pi I've designed a HAT, which provides:
An estimation of the HAT will be around 7 Euro's, excluding the Tang Nano 20k. Inlcuding the FPGA, the price would be around the 40 Euro price point.
Therefore, Litex-CNC is going to be expanded to accept more FPGA's, starting with the Sipeed Tang Nano 20k. Compared with the 5A-75B it has less outputs (28 compared to 48 for the 5A-75B), but this is still enough for a simple 3 axis machine. The big advantage is that no SMT soldering skills are required to get this board up and running.
For the Raspberry-Pi I've designed a HAT, which provides:
- 7 extended PMOD-connectors. Each connector has 4 GPIO, power rails (+5V, max 200 mA) and a buffered enable signal;
- RS489 connector for communicating with for example a VFD;
- communication between Raspberry PI and FPGA using SPI in bidirectional mode (3-wire) to save on pins;
- conforms to the HAT+ specification , including a EEPROM with settings.
An estimation of the HAT will be around 7 Euro's, excluding the Tang Nano 20k. Inlcuding the FPGA, the price would be around the 40 Euro price point.
- richcolvin
17 Jan 2025 17:56
Problems configuring 7i92TH with pncconf was created by richcolvin
Problems configuring 7i92TH with pncconf
Category: PnCConf Wizard
- gene_weber
17 Jan 2025 17:00
Replied by gene_weber on topic Raspberry Pi OS PREEMPT RT 6.13 Kernel Cookbook
Raspberry Pi OS PREEMPT RT 6.13 Kernel Cookbook
Category: Installing LinuxCNC
Rather than starting a new thread about jitter mitigation, I'm just going to add it here.
First, I'm keeping in mind that Peter Wallace said " The jitter is basically unimportant with a 7C81 unless its so bad you
get real time errors at the normal servo thread rate ."
I'm also treating the Raspberry Pi + 7C81 as a dedicated controller, not a PC. By that I mean I'm not going to be doing anything on the Pi except LinuxCNC. I may turn on WIFI to update packages, or use email to transfer a file. But I plan to even turn off WIFI before I launch LinuxCNC.
I ran several tests to see which combination of settings offered the most optimized jitter. I ran two Glxgears for all tests as I though that was reasonable, and ran the tests for long periods of time unless they looked bad early on.
I thought that turning off all unused services would decrease Jitter. So I turned off 9 of the 23 services, such as CUPS, Bluetooth, etc. To my surprise this did not decrease jitter.
Screen blank increased jitter a bit, so I turned that off. It doesn't make much sense anyway on a CNC controller.
These are the settings I added to the line already in /boot/firmware/cmdline.txt:
I tried a few others that some people recommended on various blogs. Nothing else I tried had any noticeable positive impact on jitter, and some noticeably slowed down the responsiveness of the Pi.
Turning off timer_migration did reduce jitter. What I read said that you could make this setting permanent by adding it to the boot command line, or setting it in either of two different system files. Oddly none of that worked. So I setup a cron job to disable it at boot, and that works.Add the following line:
The other thing that helped reduce jitter was changing the scheduling policy to real-time and increasing the priority. I decided to create a shell script to launch latency-histogram, and eventually linuxcnc, which changes these things on the process.
I named it rrt (run real-time). So to launch latency-histogram it's simply:
All spawned sub-processes inherit the policy and priority. So if linuxcnc is launched with rrt:all of the processes that are part of LinuxCNC have the policy of SCHED_RR and priority of 99. I used Round Robin scheduling to make sure no LinuxCNC process "starves" another.
I don't know if this will work in the end, but I'm going to give it a try. Nothing ventured, nothing gained.
Implementing all of these, here is the jitter histogram. Good enough.
First, I'm keeping in mind that Peter Wallace said " The jitter is basically unimportant with a 7C81 unless its so bad you
get real time errors at the normal servo thread rate ."
I'm also treating the Raspberry Pi + 7C81 as a dedicated controller, not a PC. By that I mean I'm not going to be doing anything on the Pi except LinuxCNC. I may turn on WIFI to update packages, or use email to transfer a file. But I plan to even turn off WIFI before I launch LinuxCNC.
I ran several tests to see which combination of settings offered the most optimized jitter. I ran two Glxgears for all tests as I though that was reasonable, and ran the tests for long periods of time unless they looked bad early on.
I thought that turning off all unused services would decrease Jitter. So I turned off 9 of the 23 services, such as CUPS, Bluetooth, etc. To my surprise this did not decrease jitter.
Screen blank increased jitter a bit, so I turned that off. It doesn't make much sense anyway on a CNC controller.
These are the settings I added to the line already in /boot/firmware/cmdline.txt:
skew_tick=1 kthread_cpus=0-2 irqaffinity=0-2 rcu_nocb_poll rcu_nocbs=3 nohz=on nohz_full=3 isolcpus=3I tried a few others that some people recommended on various blogs. Nothing else I tried had any noticeable positive impact on jitter, and some noticeably slowed down the responsiveness of the Pi.
Turning off timer_migration did reduce jitter. What I read said that you could make this setting permanent by adding it to the boot command line, or setting it in either of two different system files. Oddly none of that worked. So I setup a cron job to disable it at boot, and that works.
crontab -e@reboot sudo sysctl kernel.timer_migration=0The other thing that helped reduce jitter was changing the scheduling policy to real-time and increasing the priority. I decided to create a shell script to launch latency-histogram, and eventually linuxcnc, which changes these things on the process.
#!/bin/bash
#
# Run with the SCHED_RR real-time policy at the highest priority level (99)
# Uses chrt to switch the process policy and priority immediately after launch.
#
# Gene Weber - January 2025
#
# "The difference between SCHED_FIFO and SCHED_RR is that among tasks with the same priority,
# SCHED_RR performs a round-robin with a certain timeslice; SCHED_FIFO, instead, needs the task
# to explicitly yield the processor." -Claudio
priority=99
# Truncate $1 (the command) to 15 characters starting at 0.
command=${1:0:15}
# Execute the command line provided to rrt as a background task.
`$@` &
# Get the process ID of the command.
PID=`pgrep $command`
# Change the real-time policy to SCHED_FIFO with a priority of $priority.
sudo chrt -r -p $priority $PIDI named it rrt (run real-time). So to launch latency-histogram it's simply:
rrt latency-histogram --nobase --sbins 1000All spawned sub-processes inherit the policy and priority. So if linuxcnc is launched with rrt:
rrt linuxcncI don't know if this will work in the end, but I'm going to give it a try. Nothing ventured, nothing gained.
Implementing all of these, here is the jitter histogram. Good enough.
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