Acceleration in our pockets

[Carsten Haitzler (The Rasterman)]

On Thu, 12 Jun 2008 14:52:07 +0000 (GMT) David Samblas Martinez
<dsamblas at yahoo.es> babbled:

7m/s hard to saturate? remember - if you SATURATE it at 7m/sec - you now lost
ALL compute cycles. you spend 100% on just copying across the bus.

let me explain. while you copy data - the cpu is IDLE waiting on the bus - you
can't go do something else. if you can't copy at the full memory busy speed you
are losing EXCESS cycles compared to what you would copying the result to
system ram. you do the math.

as for 352x288 - please dig through the mail archives. i posted details on
what is possible in theory and what i have in fact measured myself. i gave
actual framerates, resolutions etc. with real video content being played. i
always said you would probably manage qvga - but never vga. (not at 25 or
30fps). it's not possible (if transporting yuv data across the bus).

i did tests too - different mp4 file, at 640x480 letting xvideo do the scaling.
i maxed out at 32fps for 320x240 - of course this will vary from file to file.
higher bitrate files will require more cpu to decode and thus will not play as
well.  320x240 @ 21fps was the limit with cpu pegged at 100% usage, video file
coming off flash. 19fps when coming from sd-card.

i never said video playback was not possible - i said it came with caveats - as
it always does unless you have a hopelessly overpowered system. you give up
complexity, resolution or framerate - always. just a question of which one and
how much. a simpler codec or lower bitrate will win you on the compute side and
this can vary from video to video (a video that is mostly black darkness will
decode much faster than one with lots of motion, details and colour).

so please let me know where i have been "so wrong"? comparing apples to apples?

> I copy & paste an very interesting comment from balrog ,seems that I have
> become his(totally voluntary) mail list assistant ;)
> 
> Rasterman..... 352x288 25 fps..... something to say?
> 
> --------------Begin of comment-----------------------
> #  balrog Says:
> June 11, 2008 at 4:20 am
> 
> Mikko: I hope we’ll eventually see more than just MPEG support on the Glamo
> (3D stuff etc). Regarding QVGA at this moment it’s a conjecture… and at this
> moment it’s confirmed. I’ve just tried QVGA and while the colours became a
> bit undersaturated and gamma seems to be too high, I got full 25fps playback
> both straight and with rotation, hw-scalled from 352×288 to 240×320 or
> 320×240. Unfortunately tslib seems to not have noticed the change and still
> reports touch coords in 0…640 range.
> 
> i_m_bison: Darude_-_Feel_the_beat.mp4 (the video is ok, the music not so
> much:))
> 
> tuXXX: I was wondering about that too, but rather MPEG decoding on the CPU
> and scaling/rotation on Glamo - this would allow us to do more stuff
> concurrently. The other way, as Mikko notes you transfer the video to the
> VRAM, then back to the RAM and then back to the VRAM and the bus becomes a
> bottleneck. In the current setup and normal usage I don’t agree with Raster
> that 7M/s is a bottleneck, it’s rather hard to saturate with normal X usage
> even coupled with SD card traffic etc.
> ----------End of comment------------------------------
> Raster, I'm really happy that you where so wrong at this topic
> 
> --- El jue, 12/6/08, Joerg Reisenweber <joerg at openmoko.org> escribió:
> 
> > De: Joerg Reisenweber <joerg at openmoko.org>
> > Asunto: Re: Acceleration in our pockets
> > Para: community at lists.openmoko.org
> > CC: "Peter Nijs" <peter at familienijs.be>
> > Fecha: jueves, 12 junio, 2008 2:37
> > Am Do  12. Juni 2008 schrieb Peter Nijs:
> > > Isn't the shared bus an advantage because now it
> > can use DMA? Maybe that's 
> > > why  
> > > it is possible to hook up an sd-card to the glamo
> > anyway. I see no other 
> > > explanation why one would put an sd cardreader in a
> > graphics ship. Please 
> > > tell me if and why I'm wrong.
> > > 
> > > Peter
> > > 
> > Good point. Would make perfect sense...
> > /j_______________________________________________
> > Openmoko community mailing list
> > community at lists.openmoko.org
> > http://lists.openmoko.org/mailman/listinfo/community
> 
> 
>       ______________________________________________ 
> Enviado desde Correo Yahoo! La bandeja de entrada más inteligente.
> 
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-- 
Carsten Haitzler (The Rasterman) <raster at openmoko.org>