Re: Audio playback speed issue on sam460ex and pegasos2

[BALATON Zoltan]

On Sun, 12 Mar 2023, Volker Rümelin wrote:
> Am 12.03.23 um 16:34 schrieb BALATON Zoltan:
> > On Sun, 12 Mar 2023, Volker Rümelin wrote:
> > > Am 12.03.23 um 14:23 schrieb BALATON Zoltan:
> > > > On Sun, 12 Mar 2023, Volker Rümelin wrote:
> > > > > Am 11.03.23 um 23:54 schrieb BALATON Zoltan:
> > > > > > Hello,
> > > > > >
> > > > > > I've noticed before that since commit a806f95904cdb audio plays slower 
> > > > > > (like half speed) under AmigaOS on sam460ex with ES1370 but I did not 
> > > > > > have any other guests to reproduce it and verify this with so I did not 
> > > > > > report that yet. Now that we can also test with pegasos2 and via-ac97 
> > > > > > it does not play slower on that machine neither with ES1370 not 
> > > > > > via-ac97 but still can reproduce it with sam460ex.
> > > > > >
> > > > > > But on another host it seems to play faster with pegasos2. Here is a 
> > > > > > video taken by Rene demonstrating the problem: 
> > > > > > https://youtu.be/Rg5buzDqGuk So there seems to be a problem with 
> > > > > > playback speed here but I'm not sure if this is related to AmigaOS or 
> > > > > > something else.
> > > > > >
> > > > > > At least we have some issue with AmigaOS on sam460ex and ES1370 playing 
> > > > > > too slow since commit a806f95904cdb on Linux with alsa backend and may 
> > > > > > also have an issue with sound being too fast on pegasos2 with 
> > > > > > coreaudio. However Rene said that recording it with a screen recorder 
> > > > > > did not show the problem, only when playing it normally, that's why the 
> > > > > > video is taken with a camera. I can't understand how that's possible 
> > > > > > but maybe you have some idea to at least how to test this further to 
> > > > > > find out more what's happening here or if you can see anything that can 
> > > > > > cause playback speed issues with these machines.
> > > > > >
> > > > > > So far I've reproduced obviously slow speed with AmigaOS on sam460ex 
> > > > > > with ES1370 on Linux with alsa. The MorphOS and AmigaOS on pegasos2 
> > > > > > with via-ac97 or ES1370 (latter only works with AmigaOS) seems to be OK 
> > > > > > to me on my machine but is playing too fast in Rene's video.
> > > > > >
> > > > > > Could this be related to some differentce in host's sampling rate or 
> > > > > > some other settings somewhere? I have defaults.pcm.dmix.rate 44100 in 
> > > > > > /etc/asound.conf while Rene is using whatever macOS does with 
> > > > > > coreaudio.
> > > > > > Any ideas what to check further?
> > > > >
> > > > > Hi,
> > > > >
> > > > > perhaps this issue is similar to the Linux guest driver issue with an 
> > > > > AC97 device. The Linux driver tries to measure the AC97 clock frequency. 
> > > > > It starts playback with a certain amount of audio frames and measures 
> > > > > the time needed for playback. Since QEMU is not a cycle exact simulation 
> > > > > the result is always wrong. Before my latency reducing patches the 
> > > > > result was always way off and the Linux driver rejected the measurement 
> > > > > and used a clock frequency of 48000Hz. Now the driver sometimes believes 
> > > > > the measurement is correct and adjusts the clock frequency.
> > > >
> > > > I don't think that's the case with the AmigaOS driver. I don't know for 
> > > > sure what exactly does that driver do but it is probably similiar to the 
> > > > AROS driver which is here (the via-ac97 is one level up from that): 
> > > > https://github.com/aros-development-team/AROS/tree/master/workbench/devs/AHI/Drivers/SB128 
> > > > and I don's see anything like that in it. AROS doesn't run on pegasos2 
> > > > yet so I can't test with that. It should work with sam460ex which I've 
> > > > tried but the SB128 driver used for ES1370 seems to have endianness 
> > > > problems and only works on pc machine, not on big-endian PPC machines (a 
> > > > lot of AROS network drivers have the same problem, these seem to be 
> > > > mostly tested on PC only). On sam460ex it detects the card but doesn't 
> > > > make sound but works with on the pc machine.
> > > >
> > > > But the question remains how commit a806f95904cdb could change playback 
> > > > speed as the problem with sam460ex is bisectable to that commit.
> > >
> > > To change the playback speed you have to remove or add audio frames from 
> > > or to the audio stream. At the moment I don't see how this patch can 
> > > change the playback speed. I also don't see how this patch could change 
> > > the audio backend sample frequency. Do you think there is a way to 
> > > reproduce this issue on my computer?
> >
> > The reproducer I know needs AmigaOS license for sam460ex. If you don't have 
> > that maybe it can be also reproduced with Linux guest but I don't know a 
> > good distro that supported sam460ex (current ones probably don't as PPC32 
> > is quite dead so maybe some older ones). The manufacturer's site:
> > https://www.acube-systems.biz/index.php?page=hardware&pid=5
> > links to a site in downloads section with some Linux kernels but these seem 
> > to be outdated and don't know which could work. AROS should have a similar 
> > driver and I thought that could help but it does not make sound likely due 
> > to endianness issues as I've wrote before. So this is probably doesn't help 
> > much as the only easy way I know needs a closed source OS.
>
> Debugging will be slow without a reproducer on my computer. I'll have a look 
> at the link you provided.

Problem with most of those may be that they need an ATI Radeon graphics 
card but we don't emulate it enough in QEMU yet to work with those so it 
may be difficult to get those running. Maybe booting the kernel from 
command line with -kernel and -append to get output on serial could work 
as the boot selector used on sam460ex also misses a way to edit options 
of menu items.

The only other image that seems to boot with the default SM502 graphics 
I've found is this one: 
https://mirrors.ircam.fr/pub/crux-ppc/2.7/crux-ppc-2.7a.iso

but this has no sound support in its kernel so you may need to compile it 
to add an ES1370 driver if one was available back then. The sources and 
configs are on the iso but this does not seem to be an easy way either.

There may be other PPC Linux images that work but I don't know about them 
as I was mostly focusing on Amiga like OSes and make sure they run on 
sam460ex so did not test sound with Linux. I was trying to find an easier 
way but I could only come up with the above.

It's probably not a big issue now that pegasos2 also has sound, maybe more 
people want to use that instead as it's faster.

> > > > > This can be fixed with the kernel command-line argument 
> > > > > snd_intel8x0.ac97_clock=48000.
> > > > >
> > > > > If AmigaOS also tries to measure the audio clock frequency, it may help 
> > > > > to increase the playback latency to make the measurement worse. I would 
> > > > > start with -audiodev coreaudio,id=audio0,out.buffer-count=12. The 
> > > > > default buffer count is 4.
> > > >
> > > > Are these options documented somewhere? I don't even know they exist and 
> > > > which one to tune for different results so if this knowledge is only 
> > > > something you have now it would be a great contribution to put it in some 
> > > > docs for reference. Or if this is already described somewhere maybe it 
> > > > should be made more prominent as I don't even know where to look for it. 
> > > > Maybe also some generic intro on how the audio infrastructure in QEMU 
> > > > works would be helpful too so one can understand what the options tweak.
> > >
> > > The QEMU documentation describes most of the options. But there is no 
> > > detailed description of the function. I have read the code.
> >
> > Where are these in the docs? I could not find it even by searching under 
> > qemu/docs.
>
> https://www.qemu.org/docs/master/system/invocation.html
>
> Please search for coreaudio or alsa.

OK, that's basically the -help output, I've found it in qemu-options.hx in 
the source. But these don't quite tell me what those options are. E.g. 
for alsa:

in|out.period-length=usecs
    Sets the period length in microseconds.

in|out.try-poll=on|off
    Attempt to use poll mode with the device. Default is on.

But what is period length or poll mode and when do I have to tweak those 
and what are meaningful values? You've told me before that the crackling I 
get with alsa is because of try-poll and better turn that off. Why is the 
default on then? Can we set it to off by default? (I could try to make a 
patch but I don't know if that would make sense at all.) So maybe what's 
missing is some generic description on how all this works and what the 
parameters control in the big picture. I'm not saying you have to write 
that but if you are the only one who knows now then maybe nobody else can 
write that doc. If there are somebody else who knows these it would help 
to get some introduction somewhere we can refer to.

Regards,
BALATON Zoltan