Use only a few bds.

Use only a few bds.

[Shaju Abraham]

Hi all,

    In our study that we are doing abt latency of sound cards, we want
to have a situation where I do not want to use all of the 32 bds
available. we want to use say only 4 or 8 of the bds with each bd
pointing to only a small fragment of data.( This is basically to make
the card interrupt frequently and will also should not be able to
proceed if the interrupts raised by the past bds have not been serviced.
So want to restrict it to 4 or 8 ) .

It will be of great help if you can help us on the following two points.

            i)  What is the significance of ICH_MAX_FRAGS?  ( It seems
to be used only for the allocation of pages for the buffer and for
little else during the actual functioning of the card.)

            ii)    What is the significance of ICH_REG_LVI_MASK?  (This
is more used during the actual functioning of the card & is used in the
interrupt service sub-routine to update the lvi.)  It is by default 0x1f
. Is this 'cos it can be used to address the 32 bds available.  I
changed this to 3 and 7 . I observed that this makes the card to use
only 4 or 8 of the bds available. Am I correct in this conclusion?  If I
do this, I get some noise. Is this because of the interrupts raised by
the unused bds?

    If I am wrong abt all this, how should I go abt my idea of using
only 4 or 8 of the bds available?

Thanx,
--Shaju




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Re: Use only a few bds.

[Jaroslav Kysela]

On Thu, 22 Aug 2002, Shaju Abraham wrote:

> Hi all,
> 
>     In our study that we are doing abt latency of sound cards, we want
> to have a situation where I do not want to use all of the 32 bds
> available. we want to use say only 4 or 8 of the bds with each bd
> pointing to only a small fragment of data.( This is basically to make
> the card interrupt frequently and will also should not be able to
> proceed if the interrupts raised by the past bds have not been serviced.
> So want to restrict it to 4 or 8 ) .
> 
> It will be of great help if you can help us on the following two points.
> 
>             i)  What is the significance of ICH_MAX_FRAGS?  ( It seems
> to be used only for the allocation of pages for the buffer and for
> little else during the actual functioning of the card.)
> 
>             ii)    What is the significance of ICH_REG_LVI_MASK?  (This
> is more used during the actual functioning of the card & is used in the
> interrupt service sub-routine to update the lvi.)  It is by default 0x1f
> . Is this 'cos it can be used to address the 32 bds available.  I
> changed this to 3 and 7 . I observed that this makes the card to use
> only 4 or 8 of the bds available. Am I correct in this conclusion?  If I
> do this, I get some noise. Is this because of the interrupts raised by
> the unused bds?
> 
>     If I am wrong abt all this, how should I go abt my idea of using
> only 4 or 8 of the bds available?

I'm rewriting the intel8x0 driver to use scatter-gather DMA access and 
adding support for I845. So these question will be obsolete after a few days.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project  http://www.alsa-project.org
SuSE Linux    http://www.suse.com



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