Re: pointer callback in pcm

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

On Sat, 2006-03-11 at 15:42 +0000, James Courtier-Dutton wrote:


> 2) start DMA transfer of one period.
>     Which period you copy is the important bit here. At this point the 
> hardware will have played 1 period, so you replace the period that has 
> just played, not the period that is about to be played.

I am just sitting down to write this code now, but where in the dma
buffer should I look for this period. The relevant code at the moment
looks like this:

dma_xfer(0, runtime->dma_area + (0x1000 * dreamcastcard->clicks),
0x11000 + (0x1000 * dreamcastcard->clicks), 0x1000, 5);


(clicks is always equal to the period that has just played out ie the
code does this

Get interrupt
Reset interrupt flag on ARM7 side
dma transfer
clicks++
if (clicks == 8) clicks = 0
call pcm_elapsed
return with acknowledge interrupt


The hardware buffer begins at 0x11000 in the ARM7 space and each period
is 0x1000 in size - but I am rather assuming you can rely on the DMA
buffer (8 periods long) being filled up at 8 period intervals -is that
right?



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