Wall Clock Counter

Wall Clock Counter

[shane michael matthews]

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Hello group,

What I want to do is read the value stored in the wall clock counter on my
sound card.  Searching through the alsa documentation and source it appears
that snd_timer_read is the function I want to use.  From timer.c:

"The timer implementation uses ring buffer to store information about timing
events. In this buffer is recorded count of ticks and current tick
resolution in nanoseconds."  Is the 'ticks' referred to here the value in
the wall clock counter (It seems to always be set to 5 on my system)?  If
anyone could point me to more documentation I would greatly appreciate it.

Help is greatly appreciated,
Shane

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Re: Wall Clock Counter

[Lee Revell]

On Fri, 2006-09-15 at 09:06 -0700, shane michael matthews wrote:
> Hello group,
> 
> What I want to do is read the value stored in the wall clock counter
> on my sound card.  Searching through the alsa documentation and source
> it appears that snd_timer_read is the function I want to use.  From
> timer.c:
> 
> "The timer implementation uses ring buffer to store information about
> timing events. In this buffer is recorded count of ticks and current
> tick resolution in nanoseconds."  Is the 'ticks' referred to here the
> value in the wall clock counter (It seems to always be set to 5 on my
> system)?  If anyone could point me to more documentation I would
> greatly appreciate it. 

The answer to this will be hardware-specific.  In order for
snd_timer_read() to work there must be a low level ALSA timer
implementation for your sound device.  What soundcard do you use?

Lee



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Re: Wall Clock Counter

[Lee Revell]

On Fri, 2006-09-15 at 12:28 -0400, Lee Revell wrote:
> to work 

By "to work" I meant "to read the wall clock counter" - snd_timer_read
will work for other classes of timers like the system clock and per-PCM.

Lee


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Re: Wall Clock Counter

[shane michael matthews]

On 9/15/06, shane michael matthews <shane.michael.matthews@gmail.com> wrote:
> On 9/15/06, Lee Revell <rlrevell@joe-job.com> wrote:
> >  On Fri, 2006-09-15 at 09:06 -0700, shane michael matthews wrote:
> > > Hello group,
> > >
> > > What I want to do is read the value stored in the wall clock counter
> > > on my sound card.  Searching through the alsa documentation and source
> > > it appears that snd_timer_read is the function I want to use.  From
> > > timer.c:
> > >
> > > "The timer implementation uses ring buffer to store information about
> > > timing events. In this buffer is recorded count of ticks and current
> > > tick resolution in nanoseconds."  Is the 'ticks' referred to here the
> > > value in the wall clock counter (It seems to always be set to 5 on my
> > > system)?  If anyone could point me to more documentation I would
> > > greatly appreciate it.
> >
> > The answer to this will be hardware-specific.  In order for
> > snd_timer_read() to work there must be a low level ALSA timer
> > implementation for your sound device.  What soundcard do you use?
> >
> > Lee

The device is:
# lspci
00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High
Definition Audio Controller (rev 01)

I found a manual at:   http://www.intel.com/design/chipsets/manuals/307017.htm
On page 47 it discusses the wall clock.

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Re: Wall Clock Counter

[Clemens Ladisch]

shane michael matthews wrote:
> > > > What I want to do is read the value stored in the wall clock counter
> > > > on my sound card.  Searching through the alsa documentation and source
> > > > it appears that snd_timer_read is the function I want to use.
> 
> The device is:
> 00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High
> Definition Audio Controller (rev 01)

ALSA timers require that the device can issue interrupts after some
specified interval.  Your HDA controller cannot.

What do you want to use the wall clock counter for?


Regards,
Clemens

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Re: Wall Clock Counter

[Clemens Ladisch]

shane michael matthews wrote:
> What I want to do is read the value stored in the wall clock counter on my
> sound card.  Searching through the alsa documentation and source it appears
> that snd_timer_read is the function I want to use.

ALSA timers are interval timers.  There is no device-independent API
for getting a wall clock counter value.

If you want to synchronize to a PCM device, you can use the hw_ptr value
as a wall clock counter.


HTH
Clemens

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