[linux-audio-dev] synthesis on gp2x .. (was Fwd: RE: [gpx-dev] hardware interfaces)

[David Olofson]

On Thursday 12 January 2006 18:06, Jay Vaughan wrote:
> 
> >Then again, the DSP code usually accounts for just a fraction of
> >the code of a full application.
> 
> .. unless you put such DSP code in certain 'key infrastructure' 
> components of the system ..

Still shouldn't be much code to change - but someone still has to 
actually do it.


> >And heavy duty, DSP centric applications
> >(ie ones with lots of DSP code) probably won't be of much use
> >without a GFLOPS class CPU anyway.
> >I would think you can compile and run them on just about anything -
> >but without proper FP support (that is, an extremely fast integer
> >CPU + FP emulation, or "anything" with a proper FPU), they won't
> >run fast enough to do anything useful, unless all DSP code is
> >translated to integer/fixed point.
> 
> its amazing though, how there are good quality examples of audio/DSP 
> code which don't require FP .. which do in fact use integer/fixed 
> point math .. and which function just fine in cheap hardware ..

Well, I decided to do it the hard (integer) way in the real time part 
of Audiality, but as maximum portability was a requirement, I had to 
do it in pure C - and that's certainly no fun, especially not on 
compilers without long long support. (MUL and DIV are so much nicer 
in asm, but AFAIK, no high level languages allow you to make proper 
use of it. :-/ )

The more interesting part, the modular synth engine (which is to be 
usable in the real time context in future releases), uses FP, because
	1) I didn't have much time for hacking, and I'd
	   rather have it running on FP than not at all,
	2) it seems like integer processing is slower
	   than FP on most machines with proper FPUs,
	3) at the time, I knew of no integer-only hardware
	   where real time modular synthesis was viable, and
	4) most DSP stuff is easier to code in FP anyway,
	   at least as long as you can't throw in some asm.

Of course, for maximum scalability (which is a design goal, although 
not the primary one at this point), it would be best to have both FP 
and integer versions of everything - and maybe I'll do that 
eventually. However, the primary target platforms for the stuff I'm 
working on now is - guess what - x86 and PPC, so I have to focus on 
getting it to work (and preferably run fast) on those, first.


> >I can certainly understand why someone who isn't seriously
> >interested in the odd few platforms with enough oomph but no FP,
> >would lack the motivation to write and/or maintain code that is
> >relevant only on these platforms.
> 
> oh, so can i, for sure.. i mean, if you've taken the easy path once, 
> no need to consider any other path twice .. except to bemoan the 
> existence of such other paths, of course ..

If you just don't have the proper motivation to hack the code, you 
won't do it. Goes for everything, whether it's Free/Open Source or 
commercial. Unless someone needs the software, thinks hacking it 
would be fun, and/or believes there is money waiting to be made, the 
code doesn't get written.


> regardless, there certainly seems to be potential in the GP2X' lowly 
> cpu's for interesting audio hacking, and i certainly hope its 
> acceptable to the cognescenti to recognize this fact, FP or none ..

Well, I'm considering getting one, though I'm not totally sure what 
I'd use it for. (Except plain fun, of course, which is no small part 
of the whole Free/Open Source thing.)

Are there any restrictions WRT which Linux drivers are available? (I'm 
thinking external USB devices and the like.) Does it support (USB) 
keyboards and mice? (A foldable rubber keyboard and some sort of 
tracker-like sequencer could be useful. Or is there a foldable rubber 
MIDI/USB keyboard out there somewhere?)

Another thought: Is there a market for shareware games? (Ports, at 
least - it'd have to be a rather large market for dedicated game 
designs to be viable, I think.)


//David Olofson - Programmer, Composer, Open Source Advocate

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