PowerPC or XScale

PowerPC or XScale

Post by Marc » Fri, 21 Feb 2003 03:12:17



Hi all,

i am looking for a new processor with MMU for embedded linux.
Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel chip
is with 19 $ /1000 up really cheap. The Geode of Intel is very interesting,
too, but i dont know its pricing.
But i think, intel is not very conservative with its chips. After 3 years it
is very dangerous, then the processors are obsolete or a newer one, most
time not pin kompatible, is coming out.
Now my questions:
1. Which PowerPC do you prefer for embedded linux?
2. Which embedded distribution do you prefer ?
3. Which development tools do you use for cross development ?
4. Have you any experience in working with the XScale?

Thanks in advance

Marco Schramel

 
 
 

PowerPC or XScale

Post by mark » Fri, 21 Feb 2003 08:08:11


Marco,
As always, it depends on what your application is and what performance level you
need. The IBM 4xx processors are good and MontaVista supplies several LSPs(Linux
support packages). All the 405 and 440 chips have built in MMU's. The 440Gp
supports DDR, has 2 ethernets and PCI. The 405GP and 405GPr have one ethernet,
PCI, and a lot of other peripherals. The 405LP is the low power version. The
405EP looks a lot like a 405GP but with 2 ethernets. It depends on your
application.
I use the Montavista LSP tools that come with there distirbution. Since I mostly
deal with the kernel and device drivers I don't use any of the high level
application development tools. I do my development on an X86 machine running RH.
MontaVista supplies all the compilers and stuff. I can use KGDB but I usually
need to work close to the hardware level, so I use a Jtag de* called
RISCWatch. There are other de*s.
I work in for IBM in the PPC group and I do Linux porting, so my opinion is
biased. Don't ask me for sales info. You need to talk to the marketing people.
I'm just a code jockey.

Mark


> Hi all,

> i am looking for a new processor with MMU for embedded linux.
> Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel chip
> is with 19 $ /1000 up really cheap. The Geode of Intel is very interesting,
> too, but i dont know its pricing.
> But i think, intel is not very conservative with its chips. After 3 years it
> is very dangerous, then the processors are obsolete or a newer one, most
> time not pin kompatible, is coming out.
> Now my questions:
> 1. Which PowerPC do you prefer for embedded linux?
> 2. Which embedded distribution do you prefer ?
> 3. Which development tools do you use for cross development ?
> 4. Have you any experience in working with the XScale?

> Thanks in advance

> Marco Schramel


 
 
 

PowerPC or XScale

Post by Geir Frode Raane » Fri, 21 Feb 2003 15:51:11


: Hi all,

: i am looking for a new processor with MMU for embedded linux.
: Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel chip
: is with 19 $ /1000 up really cheap. The Geode of Intel is very interesting,
: too, but i dont know its pricing.

I've just had an colleague designing in an XScale 250.
Me, I use the Motorola XPC8xx series PowerPC.

My colleague is concerned about the pricing of the XScale.
He believes it is the '...first shot is free' kind of pricetag.
It is unlikely that the cost should inflate up to XPC8xx level, but
then again XPC8xx are really two for one - CPU + DSP - and some
sophisticated HDLC controllers. That cost silicon real estate.

Next, the errata sheet for XScale is said to be some 130 pages.
And we are not talking minor bugs - my colleague has loads of
XScales where the cache only works in write through mode.
That kind of makes it a WeakARM...

There was one such cache issue long back on the XPC8xx series
in combination with Linux, plus there was/is one cache coherence
issue on the IBM PPC405 series controllers.  But at time of writing,
PowerPC appares rock solid with Linux.

Guess it boild down to whether you need communication qualities or
the latest PC style gizmoes. And price of cause.

--
  ******************************************************
  Never ever underestimate the power of human stupidity.
  -Robert Anson Heinlein


  ******************************************************

 
 
 

PowerPC or XScale

Post by stefan » Fri, 21 Feb 2003 19:20:40



> Hi all,

> Now my questions:
> 1. Which PowerPC do you prefer for embedded linux?

It depends on your application. If you need a lot of peripheral such as
ethernet, HDLC and so on you'll be probably happy with Motorola. We are
using 8XX, 82XX and 7XX series.

Quote:> 2. Which embedded distribution do you prefer ?

ELDK , www.denx.de. It is free and easy to understand.

Quote:> 3. Which development tools do you use for cross development ?

Again, ELDK

I hope it can help,
stefano babic

 
 
 

PowerPC or XScale

Post by Kenneth Porte » Fri, 21 Feb 2003 21:01:07



online.com:

Quote:> i am looking for a new processor with MMU for embedded linux.

Why do you need the MMU? If you don't, take a luck at uClinux.

--
Kenneth Porter
http://www.sewingwitch.com/ken/

 
 
 

PowerPC or XScale

Post by Marc » Sat, 22 Feb 2003 03:06:49


Hi Kenneth,

first time i ve taken a look to Coldfire processors, but i think this type
are not so powerful.
I know that at the end of this year a lot of MMU-Coldfires will come out
(547x-Series).
But this is too late for me !!!!!!!!!!!!!!

Thanks for your comment

Marco




> online.com:

> > i am looking for a new processor with MMU for embedded linux.

> Why do you need the MMU? If you don't, take a luck at uClinux.

> --
> Kenneth Porter
> http://www.sewingwitch.com/ken/

 
 
 

PowerPC or XScale

Post by Marc » Sat, 22 Feb 2003 03:09:06


Hi Stefano,

thank you very much for your answer,

Which one of the PPC 8xx and 82xx do you prefer?
I am very interested in the PPC832e or the 8260.

Thanks a lot

Marco




> > Hi all,

> > Now my questions:
> > 1. Which PowerPC do you prefer for embedded linux?
> It depends on your application. If you need a lot of peripheral such as
> ethernet, HDLC and so on you'll be probably happy with Motorola. We are
> using 8XX, 82XX and 7XX series.

> > 2. Which embedded distribution do you prefer ?
> ELDK , www.denx.de. It is free and easy to understand.

> > 3. Which development tools do you use for cross development ?
> Again, ELDK

> I hope it can help,
> stefano babic

 
 
 

PowerPC or XScale

Post by stefan » Sat, 22 Feb 2003 18:12:52



> Which one of the PPC 8xx and 82xx do you prefer?
> I am very interested in the PPC832e or the 8260.

We are using 855, 860, 8260 and 755 for different projects. For low cost
projects we are using TQM modules (www.tq-group.de) for the microprocessor
part (MPC 855/860). Obviously, it depends on budget and which is the cost
of the final product. All these processors and the related peripheral (i.e.
, the internal CPM controller) are well supported in Linux.

stefano babic

 
 
 

PowerPC or XScale

Post by mark » Mon, 24 Feb 2003 07:33:54


The cache coherency in the 4xx ins not really an issue. It only affects drivers.
Many drivers have either build options or call macros that handle cache coherency
for drivers automatically. If they don't it is not a big deal most of the time to
add SW cache coherency.  It is not really a performance issue either, because it
does not take that many instructions to flush or invalidate the caches when data
is sent or received by a device. You laos can eliminate memory bus traffic because
you only flush and invalidate the cache when it is realy needed. Not having HW
cache coherency does is make the chip use a lot less power because HW cache
snooping can use a lot of logic and chip real estate.  Look at the power
consumption of processors with cache coherency like the 6xx processors and compare
them to the 4xx or an ARM. Heat can kill a design. Granted, if power and heat is
not a concern, go with what is easiest. I would look at what peripherals you want
to add, look at the heat/power budjet, and the performance target. Then decide on
the processor that bests fits. Don't pick the processor first and then try to make
the rest fit.
Mark


> : Hi all,

> : i am looking for a new processor with MMU for embedded linux.
> : Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel chip
> : is with 19 $ /1000 up really cheap. The Geode of Intel is very interesting,
> : too, but i dont know its pricing.

> I've just had an colleague designing in an XScale 250.
> Me, I use the Motorola XPC8xx series PowerPC.

> My colleague is concerned about the pricing of the XScale.
> He believes it is the '...first shot is free' kind of pricetag.
> It is unlikely that the cost should inflate up to XPC8xx level, but
> then again XPC8xx are really two for one - CPU + DSP - and some
> sophisticated HDLC controllers. That cost silicon real estate.

> Next, the errata sheet for XScale is said to be some 130 pages.
> And we are not talking minor bugs - my colleague has loads of
> XScales where the cache only works in write through mode.
> That kind of makes it a WeakARM...

> There was one such cache issue long back on the XPC8xx series
> in combination with Linux, plus there was/is one cache coherence
> issue on the IBM PPC405 series controllers.  But at time of writing,
> PowerPC appares rock solid with Linux.

> Guess it boild down to whether you need communication qualities or
> the latest PC style gizmoes. And price of cause.

> --
>   ******************************************************
>   Never ever underestimate the power of human stupidity.
>   -Robert Anson Heinlein


>   ******************************************************

 
 
 

PowerPC or XScale

Post by Roger Larsso » Mon, 24 Feb 2003 12:43:56



> Hi all,

> i am looking for a new processor with MMU for embedded linux.

ETRAX 100LX has MMU and more...
http://developer.axis.com/products/etrax100lx/index.html

Quote:> Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel
> chip is with 19 $ /1000 up really cheap. The Geode of Intel is very
> interesting, too, but i dont know its pricing.

The ETRAX is more expensive, but...

Quote:> 2. Which embedded distribution do you prefer ?
> 3. Which development tools do you use for cross development ?

Axis has its own development "environment".

Do also check out their newest "chip", with flash and...
http://developer.axis.com/products/mcm/index.html

What is the right solution for you depends on what your final
product are going to do...

/RogerL

--
Roger Larsson
Skellefte?
Sweden

 
 
 

PowerPC or XScale

Post by Matt Port » Tue, 25 Feb 2003 05:01:12



>The cache coherency in the 4xx ins not really an issue. It only affects drivers.
>Many drivers have either build options or call macros that handle cache coherency
>for drivers automatically. If they don't it is not a big deal most of the time to
>add SW cache coherency.  It is not really a performance issue either, because it
>does not take that many instructions to flush or invalidate the caches when data
>is sent or received by a device. You laos can eliminate memory bus traffic because
>you only flush and invalidate the cache when it is realy needed. Not having HW
>cache coherency does is make the chip use a lot less power because HW cache
>snooping can use a lot of logic and chip real estate.  Look at the power
>consumption of processors with cache coherency like the 6xx processors and compare
>them to the 4xx or an ARM. Heat can kill a design. Granted, if power and heat is
>not a concern, go with what is easiest. I would look at what peripherals you want
>to add, look at the heat/power budjet, and the performance target. Then decide on
>the processor that bests fits. Don't pick the processor first and then try to make
>the rest fit.

All of this is true, but there is one important thing to keep in mind
is how coherency is managed _in Linux_ on 4xx processors.  Linux requires
that consistent (cache coherent) memory be able to be allocated from an
interrupt context.  Currently, pci_alloc_consistent/consistent_alloc
will BUG if an allocation is attempted in an interrupt context.  This
is due to extra work needed to create a consistent mapping on non
cache coherent PPCs.  It is further complicated by the fact that the
fix is non-trivial...requiring making many generic VM paths in the
kernel interrupt context safe.

The outcome of this is that any driver that relies on using
pci_alloc_consistent/consistent_alloc from an interrupt context
is inherently unstable.  This has been demonstrated in a couple SCSI
drivers, which must be able to allocate consistent memory in a
low memory situation with the GFP_ATOMIC flag.  There have been
a couple threads on lkml and linuxppc-dev regarding this situation.

Regards,
--
Matt Porter

This is Linux Country. On a quiet night, you can hear Windows reboot.

 
 
 

PowerPC or XScale

Post by Bo » Wed, 05 Mar 2003 23:59:16



> Hi all,

> i am looking for a new processor with MMU for embedded linux.
> Now the focus is on PowerPC or Intel XScale PXA250 or PXA255. The intel chip
> is with 19 $ /1000 up really cheap. The Geode of Intel is very interesting,
> too, but i dont know its pricing.
> But i think, intel is not very conservative with its chips. After 3 years it
> is very dangerous, then the processors are obsolete or a newer one, most
> time not pin kompatible, is coming out.
> Now my questions:
> 1. Which PowerPC do you prefer for embedded linux?
> 2. Which embedded distribution do you prefer ?
> 3. Which development tools do you use for cross development ?
> 4. Have you any experience in working with the XScale?

> Thanks in advance

> Marco Schramel

Marco,

FYI, we will have a PXA255 Development Kit available from April based
on the new TRITON-LP and TRITON-ETN PXA255 modules - running Debian
Linux with full sources supplied.

Maybe this helps.

Bob
Strategic Test
http://www.strategic-test.com

 
 
 

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Can someone explain me what is the difference between
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powerpc-eabisim ?
ps. I'm going to port linux to a powerpc based embedded
system
Krzysztof

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