Embedded CPU.

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Hi,

When a company chooses a CPU to be embedded, why are the typical
choices PowerPC, ARM etc... Why not something like an AMD Athlon. On a
similar vein to AMD processors, they seem to have embedded processors
and the general consumer processors, why the difference? Finally,
getting hold of the general CPUs is not an issue they're available
everywhere, but how can a hobbyist get hold of a MIPS CPU, PowerPC CPU
or an ARM CPU to use in a homebrew project?

Many thanks,
Nick.


Re: Embedded CPU.

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Peripherals.  The non-amd ones tend to have more built-in peripherals
that are more suitable for an embedded device; the Athlon needs a lot
of support chips.  Now, AMD does make embedded CPUs (like the geode)
but they're not athlons.

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Digikey.  Cirrus ARM9 cpu's are $13 to $27 quantity one, including
LQFP and TQFP packages.  Freescale PPC starts at $34 but they're all
BGA.

They have pentium also, but those start at $76.

Re: Embedded CPU.
<snip>

Thanks for the fast reply! Also, I'm curious, with RISC processors
costing just as much and in some cases more than a PLD (such as a FPGA
or CPLD), why don't companies go with a PLD and just get the cores
they require?

Thanks again,
Nick.


Re: Embedded CPU.
snipped-for-privacy@googlemail.com says...
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Some do, but most "standard" cores, like an ARM, need to be licensed at
fairly high cost.  Unless you are building a piece of consumer
electronics that will sell in quantities of 100's of thousands, it may
not be cost effective compared to a working, debugged, and documented
processor.

--Gene

Re: Embedded CPU.
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Also consider the fact that a PLD capable of implementing and ARM5 is
usually more expensive than a low cost ARM5 in the first place. Don't
even begin to talk about more complex processors like the PowerPC.

Implementing off the shelf CPUs uses up lots of PLD space. The
alternative, implementing special PLD friendly cut-down CPU like the
Nios is more reasonable. But the tradeoff is there are fewer
development tools for these cut-down CPUs are compared to mature off
the shelf CPUs like the ARM or PowerPC.

So, use a custom CPU on a PLD and maybe* make your hardware developers
happy or use an off the shelf CPU and definitely make your software
developers happy -- that's the tradeoff. And remember, it is software
that often slows down a project. Anything you do to slow down software
development is not good for the project.

Note: *maybe, because it may not make the guy who has to implement the
CPU happy for all the extra work he must do but it will certainly make
the board-level guys happy for having less to route.


Re: Embedded CPU.
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  Because they do not actually cost 'as much, and in some cases more'.
If you do your maths right, you'll find Microcontrollers + peripherals +
Code memory, come in cheaper than FPGA. The FPGA makes sense only
in special (lower volume) cases. Such as a special combination of
peripherals, or a special memory mapping of HW, or FPGA as FPU etc.
  It will always be cheaper to use sandard silicon, if that silicon is
able to do the task.

-jg


Re: Embedded CPU.
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Longevity, Many embedded project are not obsolete in 6 months.  The CPU
needs to be available for years.

Re: Embedded CPU.

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I have several VIA mini-ITX based computers at home and I've been
wondering why I don't see more VIA CPU's in embedded designs? Don't
they sell the bare CPU's and supporting chip-sets?

Petter

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
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Re: Embedded CPU.
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Your experience is actually the exact reverse of reality. This is to
be expected because the embedded world, being embedded, runs quietly
in the background without the world noticing.

VIA started out in the embedded business in the late 90s manufacturing
386 compatible CPUs for the embedded market where power and cost, not
speed, is the main concern. There are a number of Taiwanese companies
manufacturing x86 CPUs (one of my favourite is DM&P for the heavy
peripheral integration they do -- no need chipsets if your app is
small enough!). VIA just happened to grow large enough to be noticed
by consumers.

Chances are the point of sale system at the local supermarket runs on
VIA CPUs. Way back in 2000 I got involved in developing monitoring
systems for electric substations. Those used VIA CPUs. I know
companies manufacturing traffic lights using VIA CPUs as their master
controller. VIA CPUs are all around you, you just don't notice them
much. Their success in the embedded market is probably why they got
brave enough to venture into the consumer market.

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Typically embedded systems developers would buy them pre-soldered to
motherboards. Even for non-x86 CPUs like the ARM or PowerPC. If you're
looking for very small form factor motherboards (think credit card
sized) check out Advantech.


Re: Embedded CPU.

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I'm aware of that, but from the local industry I don't see any designs
based upon VIA CPU's. I see ARM's, PowerPC, FreeScale, etc.

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I know that some designers/applications use mini/nano/pico-itx
motherboards in their designs, but I was thinking about the
availability of bare CPUs for design-in PCBs.

Does anybody know any ditributor in Scandinavia which carry VIA CPU's
and chipsets?

Petter
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
We've slightly trimmed the long signature. Click to see the full one.
Re: Embedded CPU.

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In general you don't see many fully custom x86-based designs because
the only legitimate reason for designing in x86 is if you need to run
a GP PC OS. This means you're designing a PC. There is a great deal of
domain-specific knowledge in such a task, and so it's carried out by
specialists.


Re: Embedded CPU.

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Indeed, it has been awhile since I've seen new special-purpose x86
hardware, but it used to be more common, especially using the 8088 and
8086.  Examples of '386 and higher special-purpose designs include the
Netblazer routers (which most assuredly are not canonical PCs) and the
Netmon SNMP controller.

Regards,

Michael

Re: Embedded CPU.

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Some years ago I ported Xfree86 to an embedded PowerPC platform. The
colors and bitmap text was all wrong due to big/little-endian
ordering. In theory I don't think it would have been more difficult to
design a VIA based platform than than the PowerPC one, assuming VIA
provide decent reference designs and support.

Petter
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
We've slightly trimmed the long signature. Click to see the full one.
Re: Embedded CPU.
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You should have run that PowerPC in little endian then. You are aware
of course that the PowerPC, like the ARM that came after it, can
execute in both big and little endian modes?


Re: Embedded CPU.

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VIA seem to be ramping their efforts in this area.
http://www.via.com.tw/en/resources/pressroom/pressrelease.jsp?press_release_no14%67

I suspect Intel are about to follow into the same power-envelope, as
Intel recently sold off a chunk of their XScale business - the x86 stuff
in the labs, will be more than power competitive.
Looks like something of a resurgance of x86 into embedded, as for a
while there, they chased the GHz at all costs, and Watts were secondary.
Blade Servers, and ultra-mobile apps have pushed that along.

-jg



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<snip>

Thank you everybody for your informative answers. :)

Nick.


Re: Embedded CPU.



NickNitro wrote:

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Imagine you are building a toy with the following attributes:

One Button

One speaker

Two aaa batteries.

Push the button, it says prase one. Push it again for
phrase two.  Repeat until bored.

100 million units to be put on the shelves by Christmas.

Would you choose a 10 cent microcontroller or an Athlon?

--
Guy Macon
<http://www.guymacon.com/



Re: Embedded CPU.
On Mon, 03 Sep 2007 15:41:19 -0700, NickNitro

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Basically it's the cost. For instance I can get an ARM Cortex M3 for
less than US$6. Also it's very easy (relatively) to design with
embedded processors -- designing with an Athlon would lead to a very
complex PCB layout.

If you're talking about one-off homebrew, then you can't go past a
discarded PC motherboard. You'll even find them on the footpath when
people throw them out.

If you want to use an ARM (for instance), then you'll have to go to a
local distributor. The best value is to get an evaluation board but
even these aren't cheap. A STM32 (Cortex M3) Evaluation Board from
STMicroelectronics cost me US$250. It has:
- STM32 --  Cortex M3 core
- USB slave
- SD (MMC) card interface
- TFT Colour Graphics LCD
- Lots of I/O
- Simple keypad and joystick (lever)
- IAR Demo Compiler (limited to 32K) & IDE
- IAR J-Link JTAG Debugger

Alternatively you can order development boards from
http://www.olimex.com/ --- I know they're in Bulgaria. But a few
friends of mine have ordered their developments boards and are happy
with them.


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