[linux-audio-dev] about MIDI timing...

[Lee Revell]

On Wed, 2006-10-25 at 15:05 +0000, Chris Cannam wrote:
> Clemens:
> > Most sound cards don't have an internal timer that could be used for
> > MIDI timing.  ALSA uses whatever timer is configured, the default for
> > this is the RTC timer.
> 
> It is?  For ALSA sequencer queues?  I thought the 
> default was system timer.  Maybe it just depends on 
> the modules you have loaded. 
> 
> My impression from Rosegarden users' reports has 
> been that trying to use the ALSA sequencer with the 
> RTC timer (something I've never bothered with myself: 
> I always use a 1000Hz system timer) is a reliable way 
> to lock up your system completely, with most kernels 
> from about 2.6.13 or so onwards.
> 
> I've been meaning to investigate with the latest ALSA 
> source and at least make a decent bug report for 
> ages, but you know the way it is, there are only
> sixty hours in the day.  It would be wonderful if some 
> excellent person had fixed it in the meantime.

This is/was a bug or multiple bugs in the kernel's RTC driver.  It
started to appear around 2.6.13 because that was the kernel release
where they regressed the default timer granularity from 1ms to 2.5ms,
forcing apps like Rosegarden to switch to RTC based timing.

Should be fixed in the latest kernels.

Lee