[sdiy] Korg DSS1 DMA oscillators, the old beast!

[karl dalen]

->There seams to be a *interesting app* for the dspic
->DMA, a transfer can be trigged by a Timer event! :-)

Hint, hint, nudge, nudge?!:)

KD

>>2010-01-23 skrev Tom Wiltshire <tom at electricdruid.net>:

> Från: Tom Wiltshire <tom at electricdruid.net>
> Ämne: Re: [sdiy] Korg DSS1 DMA oscillators, the old beast!
> Till: "karl dalen" <dalenkarl at yahoo.se>
> Kopia: synth-diy at dropmix.xs4all.nl
> Datum: lördag 23 januari 2010 20.23
> 
> On 23 Jan 2010, at 15:46, karl dalen wrote:
> > 
> > It seams your trying to implement such a DMA sample
> > oscillator mechanism, the very same i was asking
> about?
> > 
> > So by fiddling with the DMA transfer interrupt rate
> one gets
> > a DMA driven oscillator? (yes we already know DMA was
> intended
> > to be used for fast data transfer).
> > 
> > Ai'nt that a very inefficient implementation?
> > 
> > There seams to be a *interesting app* for the dspic
> DMA, a transfer can
> > be trigged by a Timer event! :-)
> 
> No, sorry. I'm being much more conventional than that.
> I'm generating audio samples in blocks of sixteen. This is
> more efficient because I only have to do one set up for
> sixteen samples, and I can make better use of pointers and
> DSP instructions.
> I then need the DMA to move those samples from the DPSRAM
> to the DAC in a timely manner (e.g. at the fixed sample
> rate). The DMA is operating in "ping-pong" mode, which means
> it uses two buffers. It reads one, generates an interrupt
> when it's finished, then reads the other, generates an
> interrupt, etc etc.
> I use the DMA interrupts to set a flag telling the main
> code that one of the buffers is empty. The main code then
> runs its sample generation routine and refills it.
> At least, that's the theory. I haven't got it working yet,
> as I said.
> 
> T.
> 
> 


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