Re: [hatari-devel] DSP bug found (and maybe solved)

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 15.4.2024 12.50, Andreas Grabher wrote:
> > Am 14.04.2024 um 23:48 schrieb Laurent Sallafranque <laurent.sallafranque@xxxxxxx>:
> > I suggest the following fix in the function :
> > static void dsp_update_rn_modulo(uint32_t numreg, int16_t modifier)
> >
> > Line 1694 :
> > replace
> >      if (abs_modifier>modulo) {
> > by
> >      if (abs_modifier>modulo-1) {
> >
> >
> > In line 1673, modulo is added +1 for buffer boundaries computing.
> > But I think modulo should be -1 when tested with modifier.
> >
> > At least, Audio Fun Machine sound becomes good with this patch, but DSP programs should be tested for non regression.
> > I've tested 2 or 3 of them, but not all of them.
> >
> > @eero, could you test my patch and tell me if AFM works well for you ?
>
> Great discovery! Obviously the special case where abs_modifier equals modulo was not handled. I think the more logical solution would be
> if (abs_modifier>=modulo)

Tested Andreas version and it does indeed fix the AFM sound when 
equalizer is used!

Sonolumineszenz demo still shows (about 6k of) these warnings:
Dsp: Modulo addressing result unpredictable

I tested quite a few other demos and couple of apps & games, and things 
still seem to work as before, so it may be safe to commit before release.


	- Eero