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Posts: 72 | Thanked: 5 times | Joined on Sep 2007
#1
I have just tested the CPU of N800 (New beta OS2008),
run X terminal ,then
~ $ cat /proc/cpuinfo
result:
Processor : ARMv6-compatible Processor rev 2 (v6l)
BogoMIPS : 388.54
Features : swp half thumb fastmult vfp edsp java
CPU implementer : 0x41
CPU architecture: 6TEJ
CPU variant : 0x0
CPU part : 0xb36
CPU revision : 2
Cache type : write-back
...

From the result ,we know the frequency of CPU at OS2008 is 388.54MHz,it's higher then OS2007!


Then I want to test it under heavy load.I play the "Nokia-N810.avi" video with default Media Player ,simultaneity -run the test:
~ $ cat /proc/cpuinfo
Processor : ARMv6-compatible Processor rev 2 (v6l)
BogoMIPS : 320.37
Features : swp half thumb fastmult vfp edsp java
CPU implementer : 0x41
CPU architecture: 6TEJ
CPU variant : 0x0
CPU part : 0xb36
CPU revision : 2
Cache type : write-back
...

It become 320.37, Not 400MHz,Why?
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Moonshine's Avatar
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#2
This has all be covered in several posts already. OS2008 does increase max CPU speed to 400MHz. However IIRC the DSP runs at it's max rate when the CPU is at 330MHz.
 
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#3
Bogomips != frequency. 388 equals about 400MHz with this CPU and operating system. The N800 will change the frequency at will, depending on the load (and sometimes it'll drop down the voltage too, all to save on battery). It also has to go down to a lower frequency when it's using certain DSP (digital signal processor) operations, because the DSP must run at a frequency which is linked to the CPU frequency. If the CPU frequency is 400MHz then the DSP frequency must be reduced instead of increased, or it would go above its design limit. Nokia had this table in a presentation posted here and elsewhere:
Code:
ARM   DSP
400    133
330    220
266    177
164     85
As you can see, sometimes the ARM CPU frequency must be reduced in order to let the DSP run at its highest performance.
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#4
It would be interesting to know what percentage of the DSP decoding mp3 takes (there are some figures returned in the sysfs, but I've never really looked at them. Now's the time) and how the speed limit is applied when using the DSP. If the DSP is fast enough at 133MHz, then the ARM could be run at full speed for the video decoding.

I also remember Igor talking about an unsupported rate with both DSP at full speed and the ARM at (or perhaps) above full speed. Was that a post on itt or the mailing list/irc?
 
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#5
Well IIRC there is actually hardware support for MP3 decoding, but other supported audio formats (AAC, etc) would be a different story.
 
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#6
Originally Posted by lardman View Post
I also remember Igor talking about an unsupported rate with both DSP at full speed and the ARM at (or perhaps) above full speed. Was that a post on itt or the mailing list/irc?
At least posted on itt: http://www.internettablettalk.com/fo...2&postcount=15
quote:
"The most interesting change would probably be to run the system at the (unsupported) configuration ARM@400, DSP@266, which would make it possible to avoid the current weird op selection mechanism."
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#7
Well IIRC there is actually hardware support for MP3 decoding, but other supported audio formats (AAC, etc) would be a different story.
No, there's no explicit hw support for any audio codec, there are hw acceleration functions in the DSP that make decoding it easier (but then these functions are used by most/all audio codecs so it's nothing specific to mp3)
 
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#8
with the full release of os2008 did anyone notice changes in the cpu load?
i think it is a little slower that it was on the beta os.
i run some progs and tested the cpuload
when i am running nothing (not even desktop applets) BogoMIPS : 160.68
when i run xmms or watch a video BogoMIPS : 388.54
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#9
Originally Posted by TA-t3 View Post
At least posted on itt: http://www.internettablettalk.com/fo...2&postcount=15
quote:
"The most interesting change would probably be to run the system at the (unsupported) configuration ARM@400, DSP@266, which would make it possible to avoid the current weird op selection mechanism."
Also with one line change in kernel you can let the dsp run at 133 and cpu at 400Mhz even when dsp plays audio. So far I tried it with mp3 and dsp at 133 can decode mp3 just fine. Anyone is interested in such kernel? Would be interesting to try some really high bitrate AAC or MP3 media or try VOIP/Skype (which needs both encoder and decoder to run on dsp).

Accordin to Igor dsp needs to run at 220MHz because
The multimedia requirements are very strict and comprise some
almost-unrealistic cases of multiple streams being decoded and mixed.
That's where the extra horsepower is needed
http://lists.maemo.org/pipermail/mae...ry/013604.html
So for 'normal' use cases like playing mp3 the dsp can run at 133MHZ and ARM core at full 400Mhz.
For more details check "Frequencies scaling with OS2008" scattered threads in January archive of maemo-developers.

As for overclocking dsp to 266MHz check the same post linked above. It is a bit dangerous and may need cold flashing when something goes really wrong.
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#10
The kernel is here http://fanoush.wz.cz/maemo/kernel-2....-dsp133.tar.gz
It has sd/mmc high speed 48MHz mode enabled, extended brightness control, crypto API enabled just like any of my kernels. In addition, with this one dsp/cpu plays audio at 133/400 instead of 220/330.
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