how to find the maximum fragment size for SNDCTL_DSP_SETFRAGMENT?

how to find the maximum fragment size for SNDCTL_DSP_SETFRAGMENT?

[Britton]

The guide of 4front's web page says total_buffer_size/2.  I know the
kernel buffer size used to be defined at kernel compile time.  How does
one go about determining it now?  DSP_GETBLKSZ?  Does DSP_GETBLKSZ still
fix the block size so that the device must be closed and opened again in
order to set the fragment size?

Britton Kerin

Re: how to find the maximum fragment size for SNDCTL_DSP_SETFRAGMENT?

[Hannu Savolainen]

On Thu, 8 Jun 2000, Britton wrote:

> 
> The guide of 4front's web page says total_buffer_size/2.  I know the
> kernel buffer size used to be defined at kernel compile time.  How does
> one go about determining it now?  DSP_GETBLKSZ?
Wy would you need this information? 

If you like to get as large fragments as possible just set the fragment
size to very big. The driver will then select the largest one it could
support.

However changing the fragment size bigger than the default doesn't give
any benefit. You can always write/read multiple fragments at time to get
the same effect.

> Does DSP_GETBLKSZ still
> fix the block size so that the device must be closed and opened again in
> order to set the fragment size?
This is the current and future behaviour.

Best regards,

Hannu
-----
Hannu Savolainen (hannu@opensound.com)
http://www.opensound.com (Open Sound System (OSS))
http://www.compusonic.fi (Finnish OSS pages)

Re: how to find the maximum fragment size for SNDCTL_DSP_SETFRAGMENT?

[Britton]

On Fri, 9 Jun 2000, Hannu Savolainen wrote:
> On Thu, 8 Jun 2000, Britton wrote:
> 
> > 
> > The guide of 4front's web page says total_buffer_size/2.  I know the
> > kernel buffer size used to be defined at kernel compile time.  How does
> > one go about determining it now?  DSP_GETBLKSZ?
> Wy would you need this information? 

I'm letting my users specify the fragment size, and I try to check things
like whether what they specify is out of range before actually making the
syscall.

> If you like to get as large fragments as possible just set the fragment
> size to very big. The driver will then select the largest one it could
> support.

Ok, I didn't know it would do that.  I guess there is no real reason the
user needs to know if their large fragment size was not actually set (they
already get a warning if the fragment size they request is big enough that
it will likely cause latency).  That behavior might be something to add to
the 4front page.

> However changing the fragment size bigger than the default doesn't give
> any benefit. You can always write/read multiple fragments at time to get
> the same effect.
> 
> > Does DSP_GETBLKSZ still
> > fix the block size so that the device must be closed and opened again in
> > order to set the fragment size?
> This is the current and future behaviour.

Thanks,
Britton