Re: ALSA OSS MIDI emulation: input problems

[Takashi Iwai <tiwai@suse.de>]

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At Wed, 26 Mar 2003 17:30:09 +1030 (CST),
Jonathan Woithe wrote:
> 
> Hi all
> 
> I've been messing with the following problem on and off for the last few
> weeks.  It occurs when the OSS sequencer emulation is used with Jazz++
> 4.1.3.  In essence, incoming MIDI events from an external MIDI interface
> have their time quantised to multiples of 48 ticks, which is not very
> satisfactory.
> 
> After a lot of messing around, I think I'm starting to work out why this is.
> Jazz++ updates its play position every 48 ticks and the trigger for this is
> a SEQ_ECHO event.  When one of these arrives, jazz increments its time
> counters, sets another SEQ_ECHO event to happen in 48 ticks time and then
> finishes.  This means that in the absence of MIDI input, jazz++ time goes up
> in increments of 48 ticks.
> 
> Now, when input occurs, Jazz++ needs to know the current time, which is very
> unlikely to be a multiple of 48 ticks.  Under nateive OSS it seems that
> before the NOTEON event (for example) OSS sends a TMR_WAIT_ABS event to
> update the application on the current time - the NOTEON event then follows
> and is assumed to have occurred at the "current time" which of course will
> be the time set by the TMR_WAIT_ABS event.
> 
> The problem as I see it is that the ALSA OSS emulation does not send this
> TMR_WAIT_ABS event - it only sends the NOTEON event.  Jazz gets this and
> without any TMR_WAIT_ABS to tell it otherwise, assumes that it occured at
> the "current" time - which is always a multiple of 48 ticks.

does the attached patch cure?


Takashi

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Index: alsa-kernel/core/seq/oss/seq_oss_midi.c
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-kernel/core/seq/oss/seq_oss_midi.c,v
retrieving revision 1.8
diff -u -r1.8 seq_oss_midi.c
--- alsa-kernel/core/seq/oss/seq_oss_midi.c	12 Mar 2003 11:26:20 -0000	1.8
+++ alsa-kernel/core/seq/oss/seq_oss_midi.c	26 Mar 2003 17:51:31 -0000
@@ -593,6 +593,7 @@
 		break;
 	}
 	
+	snd_seq_oss_readq_put_timestamp(dp->readq, ev->time.tick, dp->seq_mode);
 	snd_seq_oss_readq_put_event(dp->readq, &ossev);
 
 	return 0;