LinuxCNC Rpi4 Stock Image

For the Raspberry Pi4 there is an image available from the linuxcnc for download.
This is useful to get a baseline of what latency figures we might get with a newer setup.

Patched Bootloader

However, I have found for this version that the bootloader files are not compatible if the Rpi4 has been updated with the latest EEPROM.
To fix this it's just a case of copying the start*, fixup*, bootcode.bin files across from a working vfat partition.
(bootcode.bin isn't actually used by the Pi4, but we might as well copy it at the same time)
I've placed a patched image here:

  • Warning
Attempting to do an apt upgrade does seem to break the system. It removes the boot files mentioned above and breaks wifi. I think this is related to the kernel it's trying to update. You can re-add the boot files again outside of the system, but wifi will remain broken for some reason.

Reading the forums in the future they may be moving to something like armbian. So this is really only a temporary fix, just to get something working as a benchmark. Since it's an old image and can't be updated without some messing about.

Latency

The results of

latency-histogram --nobase --sbinsize 1000 --show

Histogram

Without glxgears.

With glxgears x10

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