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Re: [fluid-dev] Caching problems on embedded device


From: Josh Green
Subject: Re: [fluid-dev] Caching problems on embedded device
Date: Thu, 17 Jul 2008 15:38:29 -0700

On Thu, 2008-07-17 at 23:23 +0200, thomasg wrote:
> Hi,
> 
> I'm using fluidsynth as backend for a small app I'm writing. I'm not a
> good C developer, but I'm trying. :-)
> My app uses the simple midi api with direct (alsa) playback, and I'm
> sending few noteon/noteoff signals.
> On my PC this works like a charm, but unfortunately I'm running into
> problems when I try to get it running on an embedded device
> (arm9tdmi / armv4t):
> As soon I send the events a little faster, or let the playback last
> longer, it starts sweeping.
> I can't tell it for sure, but it seems that this is a problem with the
> buffers.
> I get this warning: "fluidsynth: warning: Requested a period size of
> 64, got 940 instead"
> If I set the period size to 940 manually the warning goes away, but
> the problem still exists.
> Tried some different settings, but I couldn't find the reason.
> 
> Do you have any idea what's causing this?
> 
> I did a small video to demonstrate the effect, the first tunes are ok,
> the following very noisy.
> http://videos.gstaedtner.net/epiano/epiano_0.2.mkv
> 
> Thanks,
> 
> thomasg
> 

Hello,

>From listening to your video, it sounds like your system is running out
of CPU.  FluidSynth makes heavy use of floating point math.  Since the
arm9tdmi and armv4t platforms don't have a floating point unit, it
resorts to emulation, which is going to be terribly inefficient.
FluidSynth currently requires an architecture which has a floating point
unit, to be of any use.  There was some work done a long while back by
Markus Nentwig in regards to making an integer based FluidSynth.  I
think he abandoned the task at some point though.  I'm also interested
in doing embedded system work with FluidSynth.  I'd likely just look for
a platform which has a FPU though, but it might be interesting to
attempt a purely integer implementation of FluidSynth again.

Looks like a nice touch piano app in that video.  Cheers!
        Josh Green






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