Author: Christophe Theron
Date: 15:10:11 06/19/02
Go up one level in this thread
On June 19, 2002 at 15:51:40, Tom Kerrigan wrote:
>>"The PXA250 can run at 400 MHz while using the same amount of power as a 206 MHz
>>StrongARM chip. But in order for this to happen, the handheld's operating system
>>needs to be optimized for the PXA250.
>>
>>Pocket PC 2002 isn't and therefore will be limited to 200 MHz. A version of that
>>operating system that is optimized for Xscale may not be available until 2004."
>
>The PXA250 might have special power-saving logic that's controlled by the
>operating system, so the PocketPC OS might need new code to get power
>consumption down to the advertised levels (i.e., as low as a 206MHz SA). But
>just because the PocketPC OS might not be power-consumption friendly doesn't
>mean it forces the chip to run at 200MHz, which is apparently the conclusion the
>article is drawing.
>
>That's sort of like buying a 2GHz Pentium but only being able to run it at 1GHz
>when you're using Linux. Things just don't work that way.
>
>-Tom
Given that nobody here knows about the specifics of the problem, why not start
to document yourself first?
I have read this story and I also find it strange, but I have not found enough
data (and probably I did not try hard enough).
On the other hand, there are some processors that really require specific
software to get the best performances. The Crusoe processors come to mind. Both
for their processor emulation layer and power management features.
So maybe the XScale PXA250 really needs something like that. As far as I know,
the speed of this processor is constantly adjusted (hence the name "XScale"
IIRC). So it's not always running at 400MHz (for the nominal 400MHz version). It
is very well possible that this speed adjustement REQUIRES the OS to provide
some important information, like the CPU load or whatever.
So it is very well possible that PocketPC in its current version would not fully
take advantage of the XScale, while the upcoming PalmOS 5 would.
I know that the current version of PalmOS is designed to switch the processor
into sleep mode when there is no task running. Without this feature the
batteries would not last as long as they currently do. Maybe the XScale also
needs to know if the OS is idle or not in order to provide the maximum speed
only when it is needed. Or else your batteries get sucked up in 10 minutes in a
"wait for user input" loop...
Christophe
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