Linuxcnc on Raspberry

BrendaEM wrote:

Is there something about the Raspberri Pi that makes it heresy to support?

Not at all, and the Pi is supported to an extent. There is even a specific Raspberry Pi driver for the Mesa 7i90:
linuxcnc.org/docs/devel/html/man/man9/hm2_rpspi.9.html

Machinekit has a HAL driver for the RPi GPIO. I am not sure why LinuxCNC doesn't have it too. I have definitely run LinuxCNC on a Pi, and moved motors.

I am using an RPI3 with machinekit driving two PiDiCNC boards for quite some time now, it works nicely without any issues, that is until you load a 4.5MB gcode file, at that point you really get to see the shortcomings of such a system.
Had to change to software GL rendering and it is usable even with those big files.
In general for smaller machines i would use it, as i had no actual problems with it for over 4 months of heavy use.
The real problem with RPI and the likes is to much power saving options that cause to much latency, not the processing power or I/O.

It does not help, at least not noticeably. Everything on those boards is made to use as little power as possible, so they have many working states that they keep changing. They can be used with other hardware like the PiDiCNC as the servo thread is set at 1000000 or 1000 iterations per second, but i have mine set at 500000 or 2000 i/s and it works much better.

There is an image of the debian jessie machinekit version floating around the net but it is hard to find.
From my limited experience with RPI, i was extremely disappointed at how miserable the resources for it are, namely you get the RPI all happy and smiling and fire up google to look for an image to write to an SD card and just boot it up to have something, whatever, on the screen to play with aaaaaand after about 2 waisted hours you end up with nothing. Like nothing !!!! Some server images and media server editions exist that work nicely, but for some reason not that easy or obvious to find ( this is from someone who use BBS back in the day and can find damn near anything on the net.).
There are plenty of tutorials, some very nice and concise, some really messed up, but i find it beyond belief that there is so little ready for use for something that has been around for quite some time and supposedly is sold by the millions every year.
As for me i have 2 of them in use, i sincerely doubt i will buy another one any time soon.

ozzyrob wrote:

Surely the Beaglebone is a better platform for cnc comapred to a RPi ?.

I have heard that the BBB struggles to handle a user interface. The Pi has a much better graphics subsystem than the BB so does better there.

For IO it is possible to connect a Mesa 7i90 to the Pi using SPI. That gives lots of IO and even better stepping than the PRU.
Of course it adds a fair bit to the cost.

Machinekit seems to typically have realtime running on the BBB with the user interface somewhere else. The fundamental philosophy behind EMC (which eventually became LinuxCNC) was to have everything running on one off-the-shelf computer. Machinekit seem to have decided that this isn't the way to go now that there are off the shelf devices like BBB and so see it as desirable to split realtime and User Interface between two (off the shelf) machines.

Or at least that is how I understand it. I have lost track of Machinekit over the years.