Rasberry Pi?

Gotta love te free flow of info!

Frankly it is a little thin on I/O but maybe passable for simple machines.

heychris wrote:

All,

I'm a hardware engineer and have done some work with embedded linux. I was curious what the appeal is toward raspberry Pi instead of other single board PC's. I'm a fan of raspberry pi. I've got 2 on ordered. The reason I like raspberry pi is the embedded HD decoder. It's good for connecting to a TV. I'll be using mine to play movies, etc through xbmc.

Has anyone considered a different single board embedded box that has I/O?

There are more than a few really nice ARM based boards. The problem is the lack of strong real time support under Linux. So anybody building LinuxCNCfor ARM will have his work cut out for him.

I've looked in to some of the AMD Zacate based boards. Mainly for something low cost but yet capable GPU wise. Unfortunately I'm so swamped at work I barely have time to catch up on sleep on the week ends. I haven't gotten good feed back either with respect to LinuxCNC on such hardware, Zacate is rather new. I see it as a platform worth pursuing. That is due to he GPU but also as an alternative to Intel. I could see Intel pulling ATOM off the market in the future.

To be honest I don't think USB is the problem here. The board does have an I/O header that has enough I/O for a simple machine.

Rather as I see it the problems are thus:

1. The unit is ARM based. There is nothing wrong with ARM but there is the issue of real time support.
2. 
   Now while ARM isn't bad, the core they are using isn't exactly known for setting fires. It is possible that the slow core would limit the performance of any machine built with this chip.
3. 
   USB isn't the problem as it does have I/O. You may however have to write a bit of code to use it and build a custom card to exploit the serial I/O. Let's just say it isn't ready to go though I've heard that breakout boards are already on the way.
4. 
   The board has an extremely powerful GPU, in fact the ARM CPU looks like an after thought. It is as yet unknown how much of a problem this GPU would cause for real time operation. That doesn't mean don't try just that there has been issues in the i86 world.

Nice little list. Understand I'm not trying to be negative here, what I want you to understand is that using Raspberry pie in this way isn't going to be easy. You may have to port a real time kernel just to get started.

Moreso the hobby really really needs a dedicated board in this price range. It would be very nice to get LinuxCNC running on this board, even if that meant it would only be suitable for lower end machines. It is just to bad the board comes up short in a few ways. Maybe what we need is a $50 board. $50 dollars might be doable if the I/O was specifically tailored and minimal for a CNC machine. That and given ones ability to source the parts with prices the Raspberry Pie team seemed to manage.

The thing here is if you can't do it this year you might be able to next year. Prices on these sorts of embedded processors are dropping like a rock.

Note that even today there are a few bargain ARM based boards out there like the Beagle board that may be more rational choices. Note though that you still end up with the real time issues and other development challenges. Also my info on ARM and real time Linux may be outdated, but I would think that we would have heard about progress there.
2e0poz wrote:

Guys got to ask this question and i know it is down the USB whatever route but it still can not be ignored. There seems to be an opportunity here to have a self contained unit with a small footprint. even if something else like a smooth stepper was required. What's the thoughts? is anything going to happen at some point to utilise usb?

PS

I do understand why it is not used now.

I agree that a GPU focused board isn't ideal. These things continue to increase in speed and decrease in cost. I'm pretty sure ARM processors are realtime now. TI lists a couple specifically real-time.

It looks like TI has a reference design of a stepper driver made for CNC applications.

www.ti.com/tool/RDK-STEPPER
www.ti.com/tool/mdl-stepper

Guys the info you are giving out is exactly the thought provoking process i was looking for and some great answers. I'm in the middle of knocking up a small desktop job dedicated to PCB work. It would have been nice to have an all contained unit which is where i was going with this. Might just need to stick with my laptop (HP z series) that works.

Still worth keeping this thread going though as you never know somebody might take the challenge?

Thanks All

I got the 1 GHz P3 PC I'm using for LinuxCNC for free. Can't get much cheaper than that. Well, I guess they could have paid me to take it away. Not unheard of in the realm of E-Trash these days I suppose. The machine is virtually worthless for modern computer use, it isn't small, and it consumes a lot more power than an embedded solution would.

Is it enough? That would depend on what you're looking for. I have a 20000ns latency. It has been somewhat limiting, but I'm managing I suppose. Plenty of PCI ports.

Laptops are often a poor choice for real time applications because of their power management systems, and a few other attributes unique to laptops, as opposed to other form factors. I'm not saying it won't work, but it is likely to give you issues other solutions wouldn't. It will likely never work quite as well as better solutions too. Most in the know don't even bother with them.

So on that note, good luck!