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Explaining Disappointing XScale Performance In Pocket PCs
JYD writes: "I found this new article on a Pocket PC web site where Microsoft talks about why XScale Pocket PCs aren't as fast as people thought they would be. Is it the OS? The CPU not supporting ARM4 properly? I wonder if the Linux port would run faster on 400 Mhz ... or did Intel screw up the CPU?"
The Amulet group has been working for year to make a low power yet high speed asynchronous ARM processors.
The Amulet 3 runs at 120 MHz and consumes very little power. Most of all its asynchronous so when you dont have mych processing to do it just sits there consuming "no" power.
They take a hell of a beating and still run. I connected one to a hamster wheel and you can see it here running despite the power fluctuating madly.
The only reason it only goes at 120MHz is because the memory isnt fast enough.
Its a little strange that only three ARM production lisences were given out. One to intel one to motorola and one to Amulet group.
Mouse powered Chips, Open source Processors and Lego
Umm... right, that's why my PocketPC 2000 Cassiopiea E115 is now as useful as a doorstop as it has a MIPS chip in it.
When I got my PocketPC, MS touted that 'software matters' - even in their publicity. Suddenly, they ditch all the SH3 and MIPS users and just support ARM in PocketPC 2002. Not only that, but applications like Terminal Services and Messenger they won't release for the older machines. I see a lot of people saying that this is becasue PocketPC 2002 is based on CE.NET - that's not correct. PocketPC 2002 is just another revamp of PocketPC 2000, which are both based on CE 3.0. So when it all boils down, it's just Microsoft playing marketing tricks. Net result of their decision - my £450 PDA became obsolete in 18 months.
I now own a Palm.
Q: What could possibly have gone wrong?
A: While we acknowledge that some peoples' perception is of something having gone wrong, we believe that any wrongness is unavoidable.
Q: Well, some analysts say it's intel's fault
A: We have implemented what we could implement, and don't believe there is any implementable implementation that would implement significant gains.
Q: Analysts also say it will be 2004 before the issue is fixed
A: It is too early to talk about 2004. That said, we are committed to delivering a good product.
Q: This is really bad news for the Pocket PC platform
A: Yes, it is. However, fortunately the issue is so small that this really isn't bad news for the Pocket PC platform.
Cheers
-b
Well I found it and the performance is NOT 50-75 percent slower then an iPaq. From the numbers on pocketnow.com, the Toshiba e740 is actually ahead in most categories with exception of graphics. There's the real kicker. I don't think it's the Xscale so much as it's the ATI imageon graphics chip in it. This is also a new chip, and as the benchmarks prove, it's driver has a problem or so it would seem. I actually heard that it's kind of operating in a emulation mode of sorts (kind of like standard SVGA on a desktop). ATI should provide driver code to Toshiba and it can then be fixed in a flash. I have a e740 and love it so much. The Xscale is a nice chip and will indeed improve in peformance as it's flashed up, but in my book, the other features are worth more. The wireless works well, the dual slots are a godsend (WE DON'T NEED NO STEEEKIN SLED! ;) ) and the price is GREAT for what you get. All in all, I would buy another one or an updated one (like the Toshiba e550 coming out soon!). One thing I am looking for is the availability of the 3000 mah high cap battery. The standard is fine for day to day use, but when you use the wireless alot you hear a giant sukcing sound coming from the battery. The other accesory I would look for is the 99 buck adapter that goes on the bottom. You add that and you can attach a USB keyboard and also drive a SVGA monitor or a Projector with it and have your handheld run your Power Point stuff on the road.
Gorkman
This complaint was also based on the FIRST Xscale pda to EVER be released. Sure there's GOING to be problems. The iPaq started off with similar issues, but you don't hear anyone talking about it now do ya? There's alot of reasons that add up to create the total performance picture. Maybe Toshiba used cheaper internal ram? Maybe they need more memory for video (I think it has like 256 K maybe?? I don't know but I know it has dedicated video ram). The point is the performance on ONE Xscale based PocketPC does not make a prediction on how the others will perform. Also as these are flashable, we can expect even the Toshiba to get better performance as flash updates are made available.
Gorkman
No onslaught here.
:(
The Newton 2100 kicks ass. I used Palm and Windows CE before finally trying out a Newton 2x00 series. The Newton made me swoon.
It's the best damn computing device out there, PC, PDA, or otherwise. I used to do my e-mail, my diary-keeping, my word processing, etc. on my PC in Linux, but now I even write my books and do 90% of my e-mailing on my Newton 2100 directly over ethernet. I read news on it, make travel plans on it, I have my household inventory on it (in Notion)... and I read BBC World News and Slashdot on it in Newt's Cape.
The PC only gets touched every few days. The Palm and CE devices are long gone. I only regret that Apple killed the Newton, so there won't be a color version.
STOP . AMERICA . NOW
It's important to differentiate between architecture optimizations
and CPU specific optimizations. The ARMv5 instruction set is a
relatively minor architectural tweak to the ARMv4 instruction set.
The names give you the impression that it's some grand change between
v4 and v5, if a technical guy did the naming it would be ARMv4 and
ARMv4.01. ARM is playing some games with architecture naming
to protect their business position with patents in a silly way.
ARMv5 adds a couple of new instructions over v4, an instruction to count
leading zeros in a register (which a compiler would likely never
use), and a better method of switching between the ARM instruction
set and the 16-bit Thumb instruction set. The later isn't
relevant for PocketPC since Thumb mode isn't supported. I think
v5 might having a new debugging hook as well.
The new XScale parts are ARMv5te, the T is for the 16-bit Thumb
instruction set, which no one seems to care about. The "E" adds
some DSP oriented instructions that are pretty interesting for
media codecs and such. They are the MMX equivalent for the ARM
world. They likely won't improve performance of the general
purpose aspects of the platform.
I think it's a red herring to chase Microsoft for not optimizing for
the ARMv5, the changes are really small and I don't see any
performance impact, certainly not if you have to maintain another
version for all of the strongARM based products.
Now, as far as CPU specific optimizations for the PXA250 (XScale)
implementation of the ARM architecture. IMHO Intel chased
MHz and left behind a lot of good sense about system performance.
The high order bit is bus performance as others have already
pointed out.
In addition to the bus performance, Intel made many tradeoffs
to optimize for clock speed: The 7-stage pipe has a 4-clock penalty
for a mis-predicted branch. This is compared to the circuit
design heroics in the strongARM that implements "all branches
are 2-cycles". The Xscale approach is much more complicated, it
probably doesn't perform any better, but you get a high clock speed.
Intel adds clock cycles to all load/store-multiple instructions
in Xscale. This is a pretty big deal in ARM since they are
used in the entry and exit of most C functions, in memcpy(),
and any time you are moving chunks bigger than a register.
The load-use penalty is bigger in Xscale. This is a pretty big
deal in ARM. The ARM instruction set is pretty compact. It is a
RISC processor, but the combination of shifting operations
combined with ALU operations makes it possible for a good compiler
to generate reasonably compact code. As a result, it's harder
for a compiler to put instructions between a load and instructions
that use the destination of the load. This is another trade-off
in Xscale that allows a higher clock speed but hurts performance
otherwise.
I go on too long, but the DEC designed strongARM used in the SA1100
is a tour-de-force of clean implementation and balanced system
performance. It's amazing that core was designed in 1993 (I think,
someone please correct me) and is still the leader for handheld
apps. The Intel guys went after clock speed at the expense of
everything else in Xscale and it will probably never optimize well
for a platform like PocketPC.
jeff