Re: [hatari-devel] 8 runes of aerillion doesn't have sound

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 10/03/2024 à 21:45, Nicolas Pomarède a écrit :
> Le 10/03/2024 à 08:32, Laurent Sallafranque a écrit :
> > Maybe this can help.
> >
> > I use a variable : "music_sequence_index" to keep the current sample 
> > index.
> > I've traced my code and I see that "music_sequence_index" goes from 
> > 0(*8) to 2(*8) immediately at the beginning of the music,
> > which means there's an interrupt played immediately after the 
> > beginning of the music.
> >
> > The VHS intro plays a sample without interrupts.
> > I stop the music between the VHS screen and the intro of the demo.
> > The sample is bigger than the effect length, so, I stop it, load the 
> > 1st music sample into memory and start to play the music.
> >
> >
> > In the music_start code, I add #8 to "music_sequence_index" because I 
> > read this value at the beginning of the interrupt code to load the 
> > next sample.
> > I also increment by #8 this variable during each interrupt in the 
> > interrupt code.
> >
> > The traced value of 2(*8) for the variable means that there's a first 
> > interrupt triggered.
>
> Hi
>
> thanks for the information.
>
> What Hatari does at the moment is that it triggers an interrupt (TAI or 
> GPIP7) when sample start playing (this is because SNDINT signal goes 
> from idle to playing).
> And optionaly it triggers an interrupt when reaching the end of the 
> sample buffer (if value is set at $FF8901)
>
> I thought signal always goes from idle to playing when starting a sound, 
> but from what you describe it seems it's not the case, because this 
> extra interrupt at start explains why sample 1 is not played and it 
> "jumps" directly to sample 2.
>
> That would mean DMA sound triggers an interrupt at start only if FF8901 
> is not enabled to trigger an interrupt at the end (Hatari allows both at 
> the moment)
>
> I need to write a small test program for falcon that would check the 
> different cases (loop yes/no and interrupt at end yes/no), because so 
> far the lack of real documentation from Atari makes it difficult to 
> emulate.

Hi

looking at the demo, I see that the 1st sample is skipped because when 
you stop the music after the vhs-like / blue screen then dma sound 
channel goes to idle (=1) and this trigger the un-wanted gpip7 interrupt 
because bit 7 in MFP's Active edge register is set to 1 (so 0->1 
transition on GPIP7 will give an interrupt)

This is not the TOS default value, usually AER's bit 7 = 0 (transition 
on 1->0 on gpip7)

I see that at the start of the demo you save MFP content and you also do 
this :

0001fd14 0838 0007 fa01           btst.b #$0007,$fffffa01.w
0001fd1a 6608                     bne.b #$08 == $0001fd24 (T)
0001fd1c 08b8 0007 fa03           bclr.b #$0007,$fffffa03.w
0001fd22 6006                     bra.b #$06 == $0001fd2a (T)
0001fd24 08f8 0007 fa03           bset.b #$0007,$fffffa03.w
0001fd2a 08b8 0007 fa0b           bclr.b #$0007,$fffffa0b.w
0001fd30 08f8 0007 fa13           bset.b #$0007,$fffffa13.w

It checks bit7 of of GPIP7 (dma sound status) and depending on that it 
changes AER bit7. And in this case it sets AER bit7=1 insted of leaving 
it to 0 (because dma sound is idle when starting the demo from tos)

Why is this needed, can you tell what's the purpose of changing AER ?

Nicolas