Beaglebone Cape

Hey all,

I stumbled across this today, and thought I'd share. TI is currently doing a contest for "capes" (basically the same as Arduino's shields) for the Beaglebone. There's a contestant who has been designing a cape for 3D printers--five steppers, 3 high-power mosfets, 3 fan/led mosfets, three endstops, the whole shebang. His contest entry is here: [beagleboard.org] and the board layout and a basic firmware is here: [bitbucket.org].

Now, combine this with recent developments in getting LinuxCNC running on Beaglebones, this seems like it might make a nice all-in-one electronics package. Since the dream of getting Raspberry Pi to act as a server/slicer/controller has been given up and we've collectively settled for using it as a server only, do you (by this I mean anyone who has played with a Beaglebone or LinuxCNC) think this is a reasonable expectation from the Beaglebone?

The Beagle Bone has a nice lot of horsepower, although whether it is good value for money is a question. There are cheaper Linux platforms coming along all the time. The Beagle shares the same problem as the Raspberry Pi, it's built around a proprietary SOC, in the Beagle it is TI's OMAP SOC. There is always a question mark over the future of these chips, given the nature of the tech market.

So while you could build a usable solution utilising the Beagle to run Linux and its two 32 bit RISC cores programmed in assembler to achieve real time performance, it would be difficult to move to other platforms. Of course, achieving vendor lock in is an ideal goal for TI...

Running LinuxCNC is one thing, but I'm not sure these boards have enough resources to do slicing, 512MB with a filesystem on SD card is not much compared to a 4GB PC with multi-GB SATA disks. It is getting there though.

I think the general idea of having an application processor running Linux, and a smaller processor doing real time stuff is good, but I would try to make it a more generic solution.

Okay, interesting. I didn't realize the RPi or the Beaglebone relied on proprietary chips. I've just read about their open-source design, so I hadn't considered the implications of the individual components.

So with respect to the current AVR chips that are popular for reprap electronics (not to mention Arduino), aren't they proprietary chips owned by Atmel? A few minutes' googling seems to hint that truly open-source processors (such as OpenRISC) are few and far between. Is the practice then just to choose the chip that's most readily available, or is there some intermediate stage between locked down and open source that I'm failing to grasp?

Thanks for the clarifications. Sometimes the implications of the open-source movement is almost as interesting as the gadgets it's produced.

Chris

Well, regardless of the interest level, the Replicape won TI's contest, and will be manufactured. Seems like there isn't much interest in the community, but it's a nice option for someone who already has a Beaglebone or wants to play around with embedded Linux.

I'm still curious about the issues with open vs closed source chips and how they impact projects like this, though.

TopherMan Wrote:
-------------------------------------------------------
> Well, regardless of the interest level, the
> Replicape won TI's contest, and will be
> manufactured. Seems like there isn't much interest
> in the community, but it's a nice option for
> someone who already has a Beaglebone or wants to
> play around with embedded Linux.
>
> I'm still curious about the issues with open vs
> closed source chips and how they impact projects
> like this, though.

Well, I didn't mean to get puritanical about it, it is more a question of degree and practicality. There is a scale from closed to free/libre, while there are no usable libre CPU designs, "more free" is better than "less free". The practical issues revolves around community support, availability of chips/boards, and how easy it is to implement copies/derivatives. The AVR architecture is no less proprietary, but Arduino is very open, has a good community., AVR chips and Arduinos are widely available. The firmware is mostly written in C and supported by GCC, so is quite easy to move to other architectures like PIC, ARM etc.

Raspberry Pi uses a SOC that is not generally available, so the Beaglebone is better in that respect. The TI OMAP chips can be ordered from Digikey for example.

I see. I was thinking of something that sat on top of the Linux kernel, like LinuxCNC, which I thought would be slightly more portable than programming the processor directly, and would give the advantage of being self-contained. However, that's a lot of overhead, and may still be more complex compared to changing from AVR to ARM. Also, rooting around the LinuxCNC dev mailing list, it seems that getting a combination of a good kernel and a functioning Xenomai patch is not going well, so it may not materialize as quickly as I thought. Oh well, we'll see what the future holds.

Yes, Linux is great as a universal application platform, but getting enough real-time performance to run steppers is a problem. LinuxCNC acheives this with some low-level dependencies so it is only supported on two particular versions of Ubuntu. There is growing interest in real-time Linux, so in time I think it will move into mainstream support. To be useful long-term, it needs be part of mainstream distros. Otherwise, it becomes part of a rapidly aging fork. That might be OK for a one-off product, but not general use.

The combination of generic Linux + Arduino has actually worked really well for RepRap, I doubt as much progress would have been made if it had been based on a real-time Linux platform like LinuxCNC.

Yeah, in reality, I know that the arduino and upcoming ARM solutions are more than powerful enough, I just like the idea of tinkering with more powerful tools.

As far as the real-time kernels go, there has actually been some advancement there. Xenomai is a framework that runs alongside the kernel and gives it real-time functionality. With it I've got LinuxCNC running quite smoothly on a computer running 12.04 64-bit, which is rather impressive considering how often they've said that newer distros and 64bit were not priorities. Right now you have to slog through the wiki to find out how to get it all working, but hopefully the next major release will package that all together, which will keep the system much more up-to-date.

BeagleBoard have announced a game changer, the "Beagle Black" [www.electronicsweekly.com]

HIghlights :

Quote

Processor: AM335x 1GHz ARM® Cortex-A8

3D graphics accelerator
ARM Cortex-M3 for power management
2x PRU 32-bit RISC CPUs

Connectivity

USB client: power, debug and device
USB host
Ethernet
HDMI
2x 46 pin headers

Software Compatibility

Angstrom Linux
Android
Ubuntu
Cloud9 IDE on Node.js w/ BoneScript library
plus much more

For the price ($45), this seems to blow away the competition.

The "Replicape" is apparently going to be available soon, not sure of cost yet.

Yeah, I got the notification about it from element14 over the weekend. I figured I'd order one when I got home, and now they're out of stock until the end of June. I really should learn to immediately order cool new gadgets without hesitation so that I don't have to spend months feeling jealous of other people's toys. I will have to go see what the LinuxCNC people have been up to with their BeagleBone variation.