Re: LinuxPLC on an SBC

K

Thread Starter

Kevin Hodges

I think there are quite a few people who would like to see the LinuxPLC on an embedded platform. I ran across a web page several weeks ago where a poll showed over 25% of respondents use less than 32 I/O. I have found that it is difficult to justify any type of PC control with a small amount of I/O unless it requires a type of special I/O, e.g. servo control. I am hopeful that the LinuxPLC with help me break out of this paradigm.

I definitely cast my vote for the LinuxPLC on an embedded platform.

Kevin Hodges


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Since Linux can run on many SBC's, I've always assumed that some number of them would be supported. There is a minimum system size that real Linux needs, e.g. it wants an MMU and, say, a megabyte of 32-bit addressable memory. Below that there are things like uCLinux and the emerging EL/IX standard for writing real time applications that run on both Linux and compliant real time operating systems. It would be good for later versions of a Linux PLC to work on these platforms. Initial work really wants to
take advantage of the development environment of full Linux.

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W
List,

I am designing a new HW platform for our products that uses an ARM processor. Typical I/O count is only 32 to 128. The first incarnation will have about 1 Meg of Flash and 128K of SRAM. We could put up to 4M/1M, but I'd rather keep it as small as possible given the price and availability of
Flash right now. Does anybody have any info on an open-source version of RTLinux that would fit in the smallest footprint? I will need support for
Ethernet & TCP/IP; we're trying to get away from reinventing the wheel here.

Also, anyone done any work with the Gnu compiler for ARM? We've used it before on 68K series parts, but haven't tried with the ARM. Any help is
greatly appreciated and saves us lots of time.

Regards,

Willy Smith
Numatico SA
Costa Rica

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Simon Martin

<coming out of lurk mode>
Hi all,

I definitely think that the LPLC should run on a small footprint, industrialised platform for acceptance in the European market. It seems that
the US is more used to the idea of a PC in production. I've still to see it yet in Europe. Design yes, production no.

To be 100% robust though, we need to have a fixed bootable image, i.e. not rely on harddisk. This is because it can quite easily corrupt the filesystem by untimely powerdowns. This would then need the end user to know about Linux, ext2, etc. to be able to bring his PLC up.

There is a project that has developed a single diskette bootable system for routers, based on the Debian distribution, which has addressed this problem, amongst other things. I don't have the URL at the moment, but if there is interest I can look it up again.

<returning to lurk mode>

Debian GNU User
Simon Martin
Project Manager
Isys
mailto: [email protected]

There is a chasm of carbon and silicon the software cannot bridge

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Simon Martin wrote:

> To be 100% robust though, we need to have a fixed bootable image, i.e. not
> rely on harddisk. This is because it can quite easily corrupt the filesystem
> by untimely powerdowns. This would then need the end user to know about
> Linux, ext2, etc. to be able to bring his PLC up.

Most older industrial PC's that I've seen have some sort of ROM boot image with the only "hard drive" being a RAM Disk. That seems to have
changed in the past few years as now they're booting a full NT system to run production machines. Yuck.

> There is a project that has developed a single diskette bootable system for
> routers, based on the Debian distribution, which has addressed this problem,
> amongst other things. I don't have the URL at the moment, but if there is

http://www.linuxrouter.org

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Curt Wuollet

Hi Simon

Glad to hear from you! Yes, the one floppy distros are good for this. What really got me thinking was the Linux PC on a Chip with onboard
linux, failsafe mode and dual watchdog timers from zflinux. www.zflinux.com
I am looking for a way to get this in a small enough package without having to upgrade my rusty pc layout skills to multilayer smd board level. It looks like a perfect device for a robust industrial grade lplc. I'm almost excited enough to start another project. The current devel system is full size atx. It would require very little work to do with this chip, it's almost a load and go. Devise a small low pin count IO bus (like i2c, but faster) and you'd be in business.

Regards

cww

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John T. Volpe

Hi all,

I'm new the scene and maybe this has already been suggested, but how about a PC-104 system with Linux (RTLinux or Lineo or other) in flash (Disk on chip etc..). Wouldn't this be the perfect starter system. No PCB Layout! No disk (Floppy or hard) on production system ! etc. etc.

John

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Hi John,

This will probably get some people excited, but PC104 is a little too big and way too expensive for what I have in mind. Yes, I know there are
inexpensive ones, but once I get to the horsepower I want and the peripherals I want they, are a lot more expensive than using a PC.
There was one I found that has it all, even two A/D convertors. but it was $800.00 a copy. The POC (PC On a Chip) approach lowers the chip count so most of what you add is cheap stuff, connectors mostly. And if you don't need it it takes up no space. If I keep talking, I'll
eventually fire up PCB and check if it can do BGA's. I really don't need another project right now but. I'd sure like to make this happen. I've
done the feasibility a couple times before, but this chip would make it economically feasible even at low volumes.

Regards

cww

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K
I would like to see the LinuxPLC run on a SBC w/ PC104 also. I am currently using a SBC from Octagon Systems that incorporates an AMD 586-133 w/ just about everything on-board except for a network connection. It has 48 I/O on-board but
I need the PC104 for interfacing to a 3-axis servo card. Of course, this SBC may be a bit "pricy" for what others had in mind.

Kevin Hodges


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Hi John,

I think I answered this a couple of posts back. The answer is mostly money The PC104 boards I've seen large for the purpose, have stuff we don't need and don't have some stuff we need. They are also pretty high buck for a standalone and the expansions are worse. It certainly would be possible to get a board with just the right stuff and they are going that way, AMD's Elan processor powers the closest matches now. If someone does an SBC with the more recent, more highly integrated POC's we'll have a winner, especially if they are flexible on feature set. Even the zflinux MachZ which I have a burning desire to check out isn't a perfect fit as ethernet is an add on. It has almost everything else that can be on-chip, including embedded linux with RT extensions. With the new sipp disk on a chip and an ethernet chip (with dc-dc converter and such) I could build a small form factor PLC at a cost that would be in keeping with my goals and pretty close to perfect for a DIN rail mount PLC. The fail safe features and embedded Linux would be great for larger machines as well. I have even entertained thoughts of seeking funding to do a startup to fill this niche. All the PC control
companies would benefit from a design like that. Alas, I don't know anybody who has the money who is a true believer. I'm serious though, so if you
know any "angels"................

Regards

cww

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