Advanced Search

I was asked to post in this thread about a problem I encountered with installing the official LinuxCNC image for the Raspberry Pi 4b. 

The issue I had was once the image was burned to the SD and booted the monitor that I have for the RPi was skewed on the login screen. It looked like the picture below. You could make out what it was showing and could log in and it would take you to the desktop but it was also skewed. You could make out what was there and navigate to the display settings, change the resolution, and get it working, but the changes were not persistent. Everytime the RPi booted it would revert back to the skewed resolution.

It was suggested that the HDMI cable could be at fault, and this is a good suggestion. I did try a couple different HDMI cables with the same results. 

I tried a lot of things from internet searches about this problem, but nothing seemed to work, but I finally found a clue from one post in the internet that was hard to find. I wound up changing several things in the config.txt file in the top level directory of the SD card. I used a Windows laptop to make the changes. Once I had it working, I reversed the changes one by one to see which change was the one that actually fixed it. Here is what I found:

In config.txt you will find this section in there with notes about what I changed to fix it:
[pi4]
dtoverlay=vc4-kms-v3d,cma-512              Comment out this line
#dtoverlay=vc4-kms-v3d-pi4
#dtoverlay=vc4-fkms-v3d                          Uncomment this line
max_framebuffers=2
arm_boost=1
#disable_fw_kms_setup=1

As I understand it this forces the use of an older display driver.

I believe this problem was due to an incompatability between the display I was using (Cheap Chinese 10 display) and the newest driver on the RPi. Forcing it to use the older driver got it working perfectly.

BTW, I also tried the same SD card on my son's RPi 5 and had no problems even with the unmodified config.txt.

Incidentally, the display I was using is a cheap one I use as a second display when I travel for work. I bought cheap because it is likely to get busted up in luggage some day. For my final LinuxCNC display I will be using a different touch screen display. Hopefully that one will work well.

I hope this will be helpful to anyone who may encounter the same problem.

The 7c81 will be fine. The only issue the wizzard doesn't support the 7c81 but you can pick a 5i25 in the wizzard and edit the files after to suit, just replace 5i25 with 7c81 and change the loading of the driver to suit.

I actually made a "homemade clone" of a 7c81 using an FPGA board from Aliexpress and some custom boards. The only difficult part was modding the hostmot2 sources to suit. Pete from Mesa was helpful with this project and I'm very appreciative of the support he give on these projects. My reason for going this way is it was a cheaper option, freight to Australia almost doubles the price, and I was looking for a "challenge". BTW the same hardware will work with the Linuxcnc-RIO project, and with the addition on a Wiznet ethernet module it allows for an ethernet option with the Linuxcnc-RIO project but not with the standard hostmot2 firmware (that would require some work on the Linuxcnc side and the FPGA side)
github.com/ozzyrob/Linuxcnc-FPGA

When using software stepping the upper limit will depend on the base thread period you can work with on the RPi4.

All The Best
Rob

Sorry that should be
The editor makes it a pita to edit posts.

OK looked into a bit further, was getting the same messages, doesn't seem to be affecting operation.
OK I think I've found out what the issue is.
systemd-zram-generator has not been installed in the image.
thenand reboot this enables enables swap via zram.

Currently it defaults to half the available ram
On my 4gb system
Before reboot you can rotate the logs via
And then hopefully those messages should be gone and swap will be enabled. To tell the truth no one has made any mentions regarding not having any swap.

More info here
github.com/systemd/zram-generator

Many thanks for bringing this up, if you can confirm that this fixes the issue that would be fantastic. If so I'll see about getting an update image up & loaded.

I have been reading a lot about options with the RPi and LinuxCNC, and am just getting more confused so I thought I would just ask a couple of hopefully simple questions.

I have a 3-axis (sometimes 4 axis) mill currently running LinuxCNC on an OrangePi. It has been run with GRBL on an arduino, and an old PC with LinuxCNC. The current setup works okay with the OrangePi but the interface lags and I have some mods I want to eventually do to my mill. I have the newest official RPi image running on a RPi 4b. I need to eventually marry this to an external motion board but I decided to start off with software stepping using a Pi hat, but I know that won't last long. Basically I'm done screwing around and want to setup a system that is capable and expandable EASILY.

I've been looking at the Mesa 7C81 but that is probably overkill for my purposes, but if it is truly as easy as it seems it may be my final choice. So first question is if setup of the 7C81 is as easy as it seems with the PNC config wizard?

Second question I have is whether I have missed another option that is less overkill.  Here is what I eventually "complete" my mill

• LinuxCNC running with touchscreen interface without lag or problems. Would eventually like on-screen keyboard with a wireless keyboard/mouse usable if needed.
• 4 closed loop steppers (XYZ and a rotary table)
• 7 home/limit switches (2 each on XYZ, 1 on rotary table)
• Spindle control (VFD)
• Spindle encoder for tapping.
• 3 encoder wheels (for using the machine as a pseudo manual machine)  
• Maybe a dozen or so switches/buttons for input to LinuxCNC
• Only need about 40 kHz stepping rate max.
  
  Should I just stop thinking about it and buy the 7C81 when it comes back into stock? Or is there an almost as easy solution that will fit the above needs.
  
  BTW, I am also planning to CNC my lathe and would want to duplicate the setup the mill has on the lathe so I don't have to relearn anything.
  
  Thanks in advance.

Yes the rt15 image does boot and run without failure

That's great.
Now if I could ask a favour, could you do a little write up of your issue and how you resolved it in this thread:
forum.linuxcnc.org/9-installing-linuxcnc...the-rpasberry-pi-4-5

I'm attempting to create a thread that consolidates info\issues\advice for the RPi platform. So if someone has your issue I can send them to the main thread rather than trying to remember the title of your thread. This would be a great deal of help.

Yes a 7I75 will work if you have one, the sainsmart BOB is cheaper for just step/dir though

Thanks guys. I got it fixed. Not sure exactly which change did it, but here are the changes that I made to config.txt.I may test each individually to see which one it was.

First I uncommented to force VGA mode
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=1
hdmi_mode=1

Next I uncommented to boost the HDMI signal here
# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
config_hdmi_boost=4


In this section I changed from "dtoverlay=vc4-kms-v3d,cma-512" to "dtoverlay=vc4-fkms-v3d" based on a problem report I found last night.
[pi4]
#dtoverlay=vc4-kms-v3d,cma-512
#dtoverlay=vc4-kms-v3d-pi4
dtoverlay=vc4-fkms-v3d
max_framebuffers=2
arm_boost=1
#disable_fw_kms_setup=1

Very cool! If you wanted another plasma challenge, how about an ethercat plasma board powered by 24v PoE so you can mount a board that does the ArcOK input, Torch on relay and the torch voltage right at the plasma cutter itself. Add a PoE injector in your control panel amd its all self contained.

the 7I75 works and I wouldn't have problems making a mistake?

Have you tired this image ?
linuxcnc.org/iso/rpi-5-debian-bookworm-6...23-11-17-1520.img.xz

First time this has come up, I've tested this image multiple times on a 4GB RPi5, so far no issues. No reported issues with 16GB either, which I guess doesn't help your issue.
Is this preventing a full boot ?
If not is zram module loaded ?
Is there any dmesg entry for zram ?
What device are you booting from SDCARD, USB or NVME.
Is your download a good download, ie: matches the sha256 file ?

I found a couple posts earlier that were talking about using basically an or argument. Looking like this must be kind of what they were talking about.

My understanding being that this allows you to use one or the other which solves most issues.
It is weird because I was reading about using a touch probe and tool setter together as a way to do tool offsets and or just to zero the probe and I would have been sure I read that here or other linuxcnc group but maybe not.

So in a quick search it looks like XOR can be used to deal with one sensor being NO and the other being NC, but they are still only tying to the one probe function right?

I read a post where you Lcvett talked about setting offset on a cutter, facing a surface, then calibrating your probe off that surface. Which solves the one use case I can imagine for wanting to use both but it seems like a pretty janky solution.
I can see having two probes with two moving elements adds some complexity and probably some stack up. Is this just considered an unacceptable solution to calibrate Z on a probe? Or is it just that no one has bothered to implement a useful feature because it's not a priority?

A. Is there a way in HAL that only allows spindle on or probe on ? Please share HAL code if possible.
B.Used debounce value 10. Should i lower or increase this value? Hope it doesn’t affect the probe performance. Please share any inputs / experience for the same. Please can you share changes in custum.hal files.