RE: Regarding Power macG4 (DSP/Dual Processors)
RE: Regarding Power macG4 (DSP/Dual Processors)
- Subject: RE: Regarding Power macG4 (DSP/Dual Processors)
- From: email@hidden
- Date: Tue, 6 Aug 2002 03:00:21 EDT
Dear Tampi,
Chris Nebel's solution for OS X is definitely the fastest
way to disable a CPU directly, but the method doesn't
screen out other calls to the processor which may affect
the timing directly by robbing your process of attention. I
have pasted his comments below this letter.
Similiarly, in OS 9.x (booted from directly, not running as
a process under OS X), will automatically disable one
processor as I mentioned before, except if the software is
created specifically to exploit the second processor. This
has the advantage, for you, of permitting you to write
software that addresses that normally-disabled processor
for your DSP testing without any penalty of any other
overhead being placed on the processor (an advantage if you
are trying to test the concept before creating a hardware
solution using a G4-based processor, although you may
readily find that dedicated DSP's [such as TI's DSP
offerings] are both significantly cheaper and faster for
most DSP field processes).
Now, if you are trying to create software for the mac that
re-tasks the processor to act as a DSP, well, you're
possibly in luck. Apple's satellite offices normally have a
suite of various models that you can test-run software
against to establish hardware compatibility tests without
purchasing every unit on the market (a very nice phone call
and perhaps a letter may be required for access, as well as
membership in APDA or AppleDev).
Back to the question at hand: what DSP functions do you
need to create, are they time-sensitive (in other words, is
the source of the information to be DSP'd flowing live and
continuiously, or can it be stored in RAM and analyzed
whenever)?
One final word: this is not something that you are likely
to find the answer to on the AppleScript list. Instead,
consider subscribing to one of the developer's lists at
Apple for whatever development language/suite you are
using...
Best Wishes,
=-= Marc Glasgow
Chris wrote:
1. Get into Open Firmware by restarting and holding down
cmd-opt-O-F keys until you see the screen light up and the
Open Firmware prompt appears.
2. Type the following:
setenv boot-args cpus=1
mac-boot
Congratulations, you have now disabled one cpu. To turn it
back on, do the same thing but say "cpus=2" instead.
Bear in mind that unless your code is multi-threaded, it's
only going to use one cpu at a time anyway. However, it
will hop from one to the other as the scheduler feels like
it, so cache locality may affect the timing.
--Chris Nebel
AppleScript Engineering
================
Tampi wrote:
>
Dear Mark,
>
>
Thanks for the reply. Actually I am trying to implement
>
the DSP algorithms using altivec technology and I need to
>
get the time taken to run these using only one processor.
>
But I am using the Ghz PowerPC Mac ( which has dual
>
processors) and therefore I am having a problem since I
>
cannot power off one of the processors to view the
>
performance. And I might have to install Linux to evaluate
>
this after some time. Could you throw some light whether
>
its posible to power off one processor from linux?
>
>
Thanks in advance
>
>
Regards
>
>
Tampi
>
>
>email@hidden wrote:Dear Tampi,
>
>
Whether both processors are running is dependent on the
>
operating system version -- if you boot your machine in OS
>
9.2.x, the second processor is ignored except for software
>
that is explicitly written to take advantage of it (such as
>
PhotoShop). Thus, this is the easiest way to ensure your
>
times reflect one sole processor. Unfortunately, if your
>
software is OS X-specific, then this becomes problematic.
>
>
The other question is what type of DSP-based manipulation
>
are you doing? Are you sure it is handled by the processor
>
at all, and not by a DSP in a VSLI chip?
>
>
Best Wishes,
>
>
=-= Marc Glasgow
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