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

[karl dalen]

Tom Wiltshire <tom at electricdruid.net>:

> It looks like it uses the 32MHz clock and 19-bit divider to
> generate the sample rate. This presumably generates DMA
> signals/interrupts. When a interrupt arrives, the DMA
> transfers a sample from the DRAM to the DAC. The purpose of
> DMA is really to move data about *without involving the CPU*
> - speed benefits are a consequence of this. In this case,
> that's probably because the poor CPU(s) have got quite
> enough to do already.

You say this in your own DMA problem post!

> The audio DAC is pretty striaghtforward, and I've got DMA
> interrupts occurring every 16 samples. The fact this happens
> at the right speed means the DMA is getting interrupts from
> the DAC correctly.
> 
> I've stuck dummy data in the DPSRAM (The DMA RAM area)
> which is just a ramp going up and a ramp going down. If the
> DMA works correctly in ping-pong mode, I should see a
> triangle wave coming out at 1/32nd of the sample rate. But
> I'm not seeing any output from the DAC.

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! :-)

Regards
KD


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