user mode sequencer timer?

user mode sequencer timer?

[Tim Goetze]

Is it possible to register a sequencer client that acts as a timer
(not only an event consumer/producer), and if so, how would one go 
about implementing one?

tia,

tim




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Re: user mode sequencer timer?

[Takashi Iwai]

At Mon, 19 Aug 2002 09:22:10 +0200 (CEST),
Tim Goetze wrote:
> 
> Is it possible to register a sequencer client that acts as a timer
> (not only an event consumer/producer), and if so, how would one go 
> about implementing one?

timer = event producer in a certain schedule, isn't it ??
it will deliver "tick" events in a programmed rythm.


Takashi


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Re: user mode sequencer timer?

[Tim Goetze]

Takashi Iwai wrote:

>At Mon, 19 Aug 2002 09:22:10 +0200 (CEST),
>Tim Goetze wrote:
>> 
>> Is it possible to register a sequencer client that acts as a timer
>> (not only an event consumer/producer), and if so, how would one go 
>> about implementing one?
>
>timer = event producer in a certain schedule, isn't it ??
>it will deliver "tick" events in a programmed rythm.

You mean it is sufficient to emit SND_SEQ_EVENT_SETPOS_TICK or *_TIME 
periodically, and transport control events accordingly? Are these 
events then used by alsa-lib to update the queue timing information?

tim



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Re: user mode sequencer timer?

[Takashi Iwai]

At Mon, 19 Aug 2002 17:42:07 +0200 (CEST),
Tim Goetze wrote:
> 
> Takashi Iwai wrote:
> 
> >At Mon, 19 Aug 2002 09:22:10 +0200 (CEST),
> >Tim Goetze wrote:
> >> 
> >> Is it possible to register a sequencer client that acts as a timer
> >> (not only an event consumer/producer), and if so, how would one go 
> >> about implementing one?
> >
> >timer = event producer in a certain schedule, isn't it ??
> >it will deliver "tick" events in a programmed rythm.
> 
> You mean it is sufficient to emit SND_SEQ_EVENT_SETPOS_TICK or *_TIME 
> periodically, and transport control events accordingly? Are these 
> events then used by alsa-lib to update the queue timing information?

well, sorry, then i misunderstood your question.

do you mean that a sequencer client as a timer source, or as a
controller of the queue?

the former is difficult, because the queue is driven by interrupts
from a timer source.  that is, a sequencer client must give signals at
the constant and fine period.  this is not a job what a user process
does.

the latter, controlling a queue, would be feasible.
in this case, you can change the tempo or time skew dynamically by
sending events via system-timer port (0:0) to a specified queue.
but anyway, a queue must run individually from the client.

maybe i can give more specific answer if i understand your question
more clearly...


ciao,

Takashi


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Re: user mode sequencer timer?

[Tim Goetze]

Takashi Iwai wrote:

>At Mon, 19 Aug 2002 17:42:07 +0200 (CEST),
>Tim Goetze wrote:
>> 
>> Takashi Iwai wrote:
>> 
>> >At Mon, 19 Aug 2002 09:22:10 +0200 (CEST),
>> >Tim Goetze wrote:
>> >> 
>> >> Is it possible to register a sequencer client that acts as a timer
>> >> (not only an event consumer/producer), and if so, how would one go 
>> >> about implementing one?
>> >
>> >timer = event producer in a certain schedule, isn't it ??
>> >it will deliver "tick" events in a programmed rythm.
>> 
>> You mean it is sufficient to emit SND_SEQ_EVENT_SETPOS_TICK or *_TIME 
>> periodically, and transport control events accordingly? Are these 
>> events then used by alsa-lib to update the queue timing information?
>
>well, sorry, then i misunderstood your question.
>
>do you mean that a sequencer client as a timer source, or as a
>controller of the queue?
>
>the former is difficult, because the queue is driven by interrupts
>from a timer source.  that is, a sequencer client must give signals at
>the constant and fine period.  this is not a job what a user process
>does.
>
>the latter, controlling a queue, would be feasible.
>in this case, you can change the tempo or time skew dynamically by
>sending events via system-timer port (0:0) to a specified queue.
>but anyway, a queue must run individually from the client.
>
>maybe i can give more specific answer if i understand your question
>more clearly...

OK, here goes. I have a core here that processes MIDI and PCM. There's
a RTC thread that controls event timing, synced to the sample clock. 
So, internally, the application has a precise idea of the current 
tempo, tick, time and frame.

Currently, events sent to ALSA sequencer ports are sent via
snd_seq_event_output_direct(), with a 0 timestamp. 

Now what I'm looking for is a way to export this timer functionality
to the sequencer system, ie make it possible for other clients to
sync to this clock.

tim



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Re: user mode sequencer timer?

[Frank van de Pol]

On Mon, Aug 19, 2002 at 08:40:34PM +0200, Tim Goetze wrote:
> >
> >the former is difficult, because the queue is driven by interrupts
> >from a timer source.  that is, a sequencer client must give signals at
> >the constant and fine period.  this is not a job what a user process
> >does.

Just nitpicking: The monotonicy is not required. The only thing needed is
that the interval is known - so we can use dynamically variable clock
frequency :-)

> >
> >the latter, controlling a queue, would be feasible.
> >in this case, you can change the tempo or time skew dynamically by
> >sending events via system-timer port (0:0) to a specified queue.
> >but anyway, a queue must run individually from the client.
> >
> >maybe i can give more specific answer if i understand your question
> >more clearly...
> 
> OK, here goes. I have a core here that processes MIDI and PCM. There's
> a RTC thread that controls event timing, synced to the sample clock. 
> So, internally, the application has a precise idea of the current 
> tempo, tick, time and frame.
> 
> Currently, events sent to ALSA sequencer ports are sent via
> snd_seq_event_output_direct(), with a 0 timestamp. 
> 
> Now what I'm looking for is a way to export this timer functionality
> to the sequencer system, ie make it possible for other clients to
> sync to this clock.
> 
> tim
> 

If I understand you correctly you actually want to slave ALSA to your
application's timing source.

I see 2 options for it (please correct me if I'm wrong since i've been away
for too long):

- sync the timer using SND_SEQ_EVENT_SETPOS_TIME events (and optionally
  SND_SEQ_EVENT_QUEUE_SKEW). ALSA remains running it's own clock (system
  clock, rtc, external clock), following your internal clock.

- Use a PCM device as timing source (you'll need a reasonable small fragment
  size though).

- Add support for a userspace clock source eg. add some
  "SND_SEQ_EVENT_CLOCK_ADVANCE" which would trigger a timer callback (hence
  snd_seq_timer_interrupt()).


Cheers,
Frank.

-- 
+---- --- -- -  -   -    - 
| Frank van de Pol                  -o)    A-L-S-A
| FvdPol@home.nl                    /\\  Sounds good!
| http://www.alsa-project.org      _\_v
| Linux - Why use Windows if we have doors available?


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Re: user mode sequencer timer?

[Tim Goetze]

Welkom terug, Frank!

>I see 2 options for it (please correct me if I'm wrong since i've been away
>for too long):
>
>- sync the timer using SND_SEQ_EVENT_SETPOS_TIME events (and optionally
>  SND_SEQ_EVENT_QUEUE_SKEW). ALSA remains running it's own clock (system
>  clock, rtc, external clock), following your internal clock.
>
>- Use a PCM device as timing source (you'll need a reasonable small fragment
>  size though).
>
>- Add support for a userspace clock source eg. add some
>  "SND_SEQ_EVENT_CLOCK_ADVANCE" which would trigger a timer callback (hence
>  snd_seq_timer_interrupt()).

? :) That's three options, unless a PCM device already is a possible
trigger for the main sequencer timer as per first option.

Anyway, my favourite would be the last option. It would also allow
us to implement the kind of predelay soft synths need without a big
fuzz: a clock-master client would only need to advance the clock 
ahead of time.

Groetjes, Tim




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