EMC2 running on Raspberry Pi?

I would like to see a LinuxCNC distro for the stock Raspberry Pi.
I do not get why this hasn't happened yet. There's a real-time kernel patch, right?
www.frank-durr.de/?p=203

I don't why it seems like everyone is recommending doing unfocused processes and for support for a specific pieces of hardware instead of getting everyone together to support a standard Pi, with the aim that it be as flexible as LinuxCNC itself.

To see this on both the LinuxCNC forum and the Rpi forum, I feel that I've just walked in on my parents have a moment of failed intimacy. There's something going on here, but I don't know what : )

I had Maschinekit running on RPi2B (latest model). Latency is really bad, ~ 50000ns. And you need a level converter between GPIO and almost anything you try to communicate with (If you don't the GPIOs die sooner or later). You'll need a display and keyboard, too, so you end up somewhere in the range of 120.- just for a crawling slow barebone machine with the equivalent of a parallel port and bad latency. So while it's nice to play with, it's a pain to actually work with.

Better get a used T60 with dockingstation (total ~ 30.- if it's in really nice shape), install Libreboot and have a latency of ~ 2000ns. Or get a T42/T43 and have a latency of ~ 8000 ns out of the box.

andypugh wrote:

But to continue: I am not disagreeing that unless you are really short of space, there is no reason to use a Pi when a small x86 machine will work so much more easily and better.

Agree totally with Andy, but a USFF PC like a Gigabyte Brix which I use is not much bigger than the Pi (5" square) and comes with a VESA mount so you can mount it in the back of your monitor. Sure you need to buy an ethernet card as well but its a nice neat solution.

I am still running my 3D printer using uspace LinuxCNC on a Pi3, ST Microelectronics L6470 stepper drives directly on the Pi GPIO and an USB-connected STM32F103 microcontroller that controls the heaters and fans (the Pi lacks analog inputs for the thermistors anyway and the 'blue pill' boards are only $1.50-$2 on ebay). GUI is a custom one which is tailored to 3D printing, fits the Pi foundation 7" 800x480 touchscreen and which lacks the Gremlin preview (even a regular PC would suffer from previewing 50MB of short segment G-code)

This setup has been chewing G-code for hundreds of hours without any issues.

Still, I do not think the Pi is ready yet to serve as a reasonable generic CNC controller. It is simply too slow to run a full GUI comfortably, especially when there is a lot of (OpenGL) previewing going on, reliability of the SDcard as rootfs storage is questionable (my 3D printer runs an almost readonly rootfs with a tmpfs overlay), and fairly highres LCD touchpanels that plug into the MIPI port either do not exist or when they do they are terribly expensive.

As soon as you move up from a 3D printer to a lowend router or so a regular x86 provides more oomph for little more money. If it is the small form factor and tinker-ability you are interested in, maybe boards like these might work.

How I wrote before, there is one plus for RasPi and that is SPI. Over it is much more easier to communicate with board with external step generator, dac or encoder counters than over ethernet or pci. At least for hobbyists or enthusiasts.

Ethernet is not an option for the RPi anyways as ethernet is via usb.