Re: [hatari-devel] Regression in 2.0.0 RC1

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 27/10/2016 à 21:12, Christian Zietz a écrit :
> I wrote:
>
> > Nicolas Pomarède schrieb:
> >
> > > I know from another demo that if you set start=end, then sound will be
> > > played (I think dma first increases start by 1 word, then compare with
> > > end, so you will play the whole RAM if you do that, but it's possible).
> >
> > Interesting, because I don't see that (increasing before comparing) in
> > the GSTMCU schematic.
>
> I just tried the "Little Bit Insane" demo, which according to [1] is the
> "other demo" you refer to. It so seems that it sets the sound control
> register ($FFFF8901) to $3, i.e. not only enables sound but also enables
> frame repeat. It is clear from the schematic (and it also makes sense)
> that sound is not stopped when the sound address counter hits the end
> address, as long as repeat is enabled.
>
> However, with no repeat enabled ($FFFF8901 set to $1), sound should stop
> immediately when start address == end address, regardless of the actual
> value of these addresses. (I see no special case for address 0.)
>
> Now, if I only had the real hardware to verify my findings...

Indeed, I think that's the problem with the DNT intro is that they don't 
set repeat, so sound should stop and that doesn't work anymore (since 
the changes I made for the "little bit insane" demo)

> Interesting, because I don't see that (increasing before comparing) in
> the GSTMCU schematic.

I wonder what's the "algorithm" used in the GSTMCU :

 - in one case, when repeat is not set, it seems dma stops when 
start=end (or maybe it's just that dma doesn't start at all). DMA 
address doesn't increase, else we would play RAM content one time.

 - in the other case, when repeat is set and start=end too, then we see 
the address increases and we play the RAM content.

So, does the schematic shows a different behaviour to increase DMA 
address depending on whether repeat is set or not ? Why would DMA 
address increase beyond end when repeat is set ?

that's some open questions ;)

Nicolas