Challenges with off the shelf PC motherboards in embedded systems?

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My company is developing a rack-mount appliance product and is planning
to use an off the shelf Intel or AMD-based motherboard/CPU.  This
choice is based on raw horsepower and cost.

Rather than debate this decision, which is beyond my pay grade, I would
like to seek advice on the following:

1. It is important that the user-experience of this device is "embedded
system" like and not PC like.  The out-of-the-box configuration
interface is a serial port.  There will be no VGA or PS/2 or other
PC-like I/O.  There can be no BIOS screens, but there needs to be a
POST, and there needs to be a CLI-based emergency shell.  Looking on
the WEB I see that General Software specialize in embedded BIOSes.
This system will run FreeBSD as a kernel.  Does anyone have experience
with embedded FreeBSD, General Software BIOS or anything in this domain
that they can share their experience on?

2. The system will have no spinning media.  What is the preferred
embedded boot media, given an image space requirement of, say, 250MB?

3. Regarding off-the-shelf motherboards, I am assuming General Software
will tailor their embedded BIOS for a commercial motherboard.  Any

I have a great deal of experience with embedded systems, but none in
"PC architecture embedded systems".  I want the bootstrap look and feel
to be non-PC.  A restricted emergency shell if the main image is
corrupted, otherwise a bootstrap surrounded by idiot proof barriers.

I am somewhat out of my element, but I have to get this done, so if
anyone has any experience to share, that would be great.


Re: Challenges with off the shelf PC motherboards in embedded systems?

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It sounds as if you at least have the right sort of budget, if you can
seriously consider a custom BIOS. There are a few problems I
encountered using PC motherboards - the main one was power. For an
embedded system that doesn't use rotating media, the power requirements
for the board are going to be (IMHO) unnecessarily complicated. Have
you considered an x86-architecture SBC? For reasonable production
quantities, this will make the overall BOM cost lower, even though the
mobo itself will be more expensive.

Startup time is a big problem on generic PC BIOSes. Take a look at the
LinuxBIOS project. I haven't actually used that in a fielded project
but I've looked at it briefly. Our x86-based project (at a former
employer recently out of business) had a VGA display on it and the
option to connect a keyboard if necessary, so we didn't need to get too
exotic. And there were more important things to do than try to reduce
startup time.

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CompactFlash is probably easiest. USB media are doable but your custom
BIOS needs to support it as a boot option and your OS needs to be able
to cope with its backing store disappearing during USB device
enumeration - CF emulates IDE and it's much easier to integrate.

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No experience with them. I customized the BIOS on our product using the
regular OEM customization tools (startup screens, CMOS defaults).

Re: Challenges with off the shelf PC motherboards in embedded systems?

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In the PC industry, component production life time can be quite short
varying from a few months to a few years, so if you plan to produce
your end products for, say, 5 years or are required to provide
replacement systems after that, I think that you should plan for at
lest 1-2 motherboard and/or processor changes during your production
period (or stock a large number of components for further production,
when the end of life for a specific component is announced :-).

When expecting a lot of component changes during a long production
run, it would make sense to avoid too much customising, since some of
it would have to be repeated at each component change.

I think that the standard BIOS included with the motherboard should
usually be enough, since in most cases you should be able to set the
how the system behaves when the mains power is applied (automatic
boot) and ignore the "keyboard missing" error (or use a keyboard
emulator). A VGA chip on the motherboard will also reduce many BIOS
complaints about missing display adaptors.

It would also be a good idea to select a motherboard with a well
established form factor (but avoiding types that are soon going to go
out of production), so that it would be more likely that a similar
motherboard with matching outlines would be available, when the
production of the original motherboard has ended.


Re: Challenges with off the shelf PC motherboards in embedded systems?
Hallo Paul,

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That is exactly the sore point I have experienced. You have a nice
system and two years later you can't buy any more motherboards. Or some
card on it becomes unobtainable. Or the manufacturer did some "design
improvements" without telling anyone in advance. Version control can
also be a huge issue.

SBC, as someone suggested, would be a good idea and I'd at least look
into it.

As to the OS I would look for something very mature such as QNX. That
one is quite PC friendly, lots of drivers. Since John plans to run it
without VGA the OS must have a good crash worthiness as well. "The
application performed an illegal operation" with an Ok and cancel button
isn't going to cut it under these circumstances.

Regards, Joerg

Re: Challenges with off the shelf PC motherboards in embedded systems?
On Tue, 03 May 2005 19:26:19 GMT, Joerg

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Sounds familiar :-)

In the previous year, quite a few manufacturers have changed their 5 V
PCI cards (one id-slot) to the 3.3/5 V "universal" PCI card (two

In the simplest case, the device driver must be changed to accept the
new PCI bridge chip, but at least some new "universal" PCI boards
actually require the 3.3 V supply, which might not be available at
some very old systems, so in the worst case, you would also have to
change the motherboard (and possibly power supply) for the new card to
also get 3.3 V.


Re: Challenges with off the shelf PC motherboards in embedded systems?
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My employer has been shipping FreeBSD network appliances for almost a
decade.  Before this employer, I've used Linux for both network
appliances and also deeply embedded real-time control systems.  None of
these systems used a custom BIOS, although at one place I hacked up the
stock BIOS with a netboot image until the mobo vendor did it themselves.

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Do you have a good idea about acceptable failure rates?

If you're careful, rotating media will work fine and will be hard to
beat for price/megabyte.  Unless you're going into a very ugly
environment, a 2.5" notebook hard drive is fairly rugged.  If you're
going into a data center, why not use a stock 3.5" drive?  It's not the
drive hardware you need to worry about - it's what the software does
with it.  You definitely don't want one big partition that's constantly
mounted read/write.  In general, the file system isn't your friend ;)

I've also used Compact Flash and found it worked just fine, although I'd
recommend *not* letting the OS use it for a swap file.  I've found that
FlashDrives (an older technology, presents a 2.5" IDE connector)
presented a surprisingly high failure rate (over 12% per year).
DiskOnChip modules are handy, but you get a single source for those
which can always be exciting.

If you've got the money, the aerospace folks have some highly ruggedized
solid-state disk emulators.  If you've got a lot of money.

Since you have quite modest storage requirements (quarter gig) I feel
safe in recommending a high-quality Compact Flash card.  Avoid the
cheaper manufacturers unless you do per-unit thermal testing :)

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About the only really fancy BIOS feature I can think of needing is a
completely serial-port accessible BIOS.  Most of the hardcore x86 SBC
vendors offer this.  At the same time, this is mostly a convenience to
the service techs, IMHO; we would rather overnight a new unit to a
customer than expect them to tweak the BIOS.

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As bootloaders go, GRUB (used most often with Linux) is pretty easy to
tweak in a variety of ways that might meet your needs.  For my company,
though, we don't bother much beyond the simplest FreeBSD BTX bootloader
(which you can hack in Forth, if you feel inclined).  However, our boot
process is relatively complicated because we barely trust the hard
drive.  Once we can load the barest hint of the OS, we go through a
bunch of consistency checks before we start loading/starting the system
in earnest.  Our goal, instead of giving the repair tech a complete CLI
with which to repair the system, is to let the machine examine,
diagnose, and repair itself, if at all possible.  For the rare times it
can't, we offer 24 hour replacements.

There are lots of ways you can give the user a good experience.  Some of
them require expensive hardware and some require complicated software
and some of them trade off the engineering with tech support.  Knowing
which way to go depends on what your customers demand, your corporate
goals and your estimated shipping quantity.


Re: Challenges with off the shelf PC motherboards in embedded systems?
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Have you looked at small form factor boards that utilize the Pentium M or
other lower power x86 CPUs?  Often they have features you might want such
as watchdog and native CF support. < ought to
give you some ideas in this area.

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Like someone else said, maybe the Linux BIOS would be something to look
at.  Most bios can be customized though to not show anything except a logo
so that may fit your needs at a lower cost.  There's a variety of ways an
emergency shell could be implemented.  A lot of vendors in the PC market
have a separate, small, and proprietary partition on the boot media that
has this kind of function for when windows blows up.

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Some kind of solid state Flash for sure.  there's CF cards but also look
at the solid state disks that plug into a special 44-pin IDE port.  Check
out < But... if
possible, be sure that all the partitions on it are mounted read only and
it will last virtually forever.  The amount of writes this type of memory
can take is limited so keep that in mind.  You definitely do not want a
swap file on there!  Depending on data storage needs, a battery backed ram
disk may be what you need.  There are also the CF form factor micro drives
but I'm not sure what the reliability on those is (a mechanical device).




Re: Challenges with off the shelf PC motherboards in embedded systems?

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Yes, CF cards would be a better choice, in terms of price/performance.

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M-system does not make the flash chip.  They buy the NAND chips from
samsung, same as Lexer CF, for example.  M-system is charging a lot
more money for the same internal flash memory.


Re: Challenges with off the shelf PC motherboards in embedded systems?

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You cannot get close to these two factors with an embedded

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If your company is riding on this PHB decision, look for another

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In what sense is this an embedded system user experience? Maybe if
your user is controlling a nuclear power plant. Who has to connect a
serial port to configure an embedded system?

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Avoid a custom bios. The bios is designed to shelter the executing
program from broken hardware and weird peripherals. Even the concept
of BIOS is non-embedded. You will end up with a group of "gurus" that
have to maintain the bios every time the PC changes. That will be at
least once every 3 months.

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Again, what kind of embedded system is this? A CLI shell? A Cisco
router is not an embedded system. It is a limited volume control

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Long ago we tried to use a x86 clone, now bought by National and VIA,
I forget the company name (maybe Cyrix?). It had a special interrupt
to translate "normal" bios calls to their custom calls. The normal
clock frequency meant that their audio frequency was slightly off,
something no true geek would notice, but a musician did. The processor
vendor company, (I don't remember which of the above), did not have
source code for this translation code, and did not even know the
frequency was off. The Bios guy could do wonders, but what does he do
with an undocumented, and invisible instruction trap?

Even with pure Intel MOBOs, (and who would use those when a $2 cheaper
version is available?) the lifetime of the MOBO is limited and the
lifetime of chips on the MOBO is even more limited. And Intel has
cancelled processors in its 5 year embedded chip inventory, way before
5 years is up. What happens when a chipset changes and existing code

You are screwed. When you get on a chip treadmill where 100s of
millions of units are involved, no embedded app matters at all. The
big volumes will dance where they will and you will try to keep your
toes from being stepped on too often.

Like I said if your company depends on this decision to use a consumer
PC MOBO find another company fast.

Regards ~Steve

There is no "x" in my email address.

Re: Challenges with off the shelf PC motherboards in embedded systems?
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Thanks for the responses.  Lots to think about.

Here are some thoughts based on the replies so far:

1. PHBs
No PHBs here - just price/performance constraints.

2. SBCs
Single board computers don't meet the price/performance criteria. We
are very cost sensitive and need lots of horsepower. Off the shelf
motherboards fit the bill.

3. LinuxBIOS
LinuxBIOS does not support modern chipsets and also can't boot FreeBSD.
We don't want to take on such a large effort as hacking a free BIOS
into shape.

4. FreeBSD
Our product uses BSD as its base.  Has done for years.  Now we need to
package it up.

5. Compact Flash, mini disks, etc.
Thanks for the options.  Compact Flash looks good.  I'll be doing some
experiments with an IDE to CF converter (won't need to be power-on
removable).  No OS swapping/paging required.

6. Availability of motherboards
We expect motherboards to be available for 12-18 months and are
prepared for the hassle of transitions.  Our motherboard requirements
are very basic - we don't need exotic peripherals.  If the product
succeeds we may very well build our own minimal motherboard (we have
very capable hardware guys).

7. Hiding the BIOS
We don't want users play with anything that might disable the unit
accidentally.  That means setting the BIOS parameters at manufacturing
time and not letting users near it.

Thanks for the feedback.

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