Re: [PATCH 5/6 v2] sound: Add n64 driver

[Lauri Kasanen <cand@gmx.com>]

On Sun, 10 Jan 2021 18:22:50 +0100
Takashi Iwai <tiwai@suse.de> wrote:

> On Sun, 10 Jan 2021 18:03:32 +0100,
> Lauri Kasanen wrote:
> > On Sun, 10 Jan 2021 11:24:22 +0100
> > Takashi Iwai <tiwai@suse.de> wrote:
> >
> > > > At first there was no nextpos, and _pointer() always reported pos. This
> > > > didn't work, the core played through the audio at chipmunk speed. So
> > > > there must be more that I don't understand here.
> > >
> > > Try to set the periods_min=2 and the integer periods hw constraint at
> > > first, and change the pointer callback to return nextpos.  Also, at
> > > the push function, set runtime->delay = period_size as well.
> >
> > When I do all this, it still causes the chipmunk speed. Several seconds
> > of audio gets played in 0.3s or so. Sorry if this is taking too much of
> > your time, I'm a bit lost here at what the alsa core is expecting.
> >
> > Printks show the following repeats:
> > start, period size 1024
> > push, bool irq=0
> > irq fired
> > push, bool irq=1
> > pointer at 8192
> > stop
>
> Hm, is the above about the result with the pointer callback returning
> pos, not nextpos?  If so,

It was returning nextpos, but the pointer printk was in bytes. 8192
bytes = 2048 frames.

> > start, period size 1024
> > push, bool irq=0
>
> At this moment, nextpos is 1024, and it should take some time until
>
> > irq fired
>
> ... this IRQ is triggered; it must be the period time.
> Was the reported timing as expected?

It's roughly correct, but timing is not very precise, as printk itself
has heavy overhead for the 93 MHz cpu.

- Lauri