Re: [LAD] Tests directly routing pc's midi-in to midi-out

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Date	Thu, 15 Jul 2010 13:45:32 +0200
From	Robin Gareus <[hidden] at gareus dot org>
To	Ralf Mardorf <[hidden] at alice-dsl dot net>
Cc	[hidden] at lists dot linuxaudio dot org, Clemens Ladisch <[hidden] at ladisch dot de>
Follow-Up	Clemens Ladisch Re: [LAD] Tests directly routing pc's midi-in to midi-out

On 07/15/2010 01:07 PM, Ralf Mardorf wrote:
> On Thu, 2010-07-15 at 12:55 +0200, Clemens Ladisch wrote:
>> Ralf Mardorf wrote:
>>> - instead of dev.hpet.max-user-freq=64 I'll try 1024 or 2048 as Robin
>>> mentioned
>>
>> This parameter will not have any effect on anything because there is no
>> program that uses the HPET timers from userspace. 

That'd be correct if Ralf would stick to 'amidiplay' and friends for his
tests.

There are a couple of audio-tools who can use either RTC or HPET for
timing, although most of them need an option to explicitly enable it.

>> When high-resolution
>> timers are used by ALSA, this is done inside the kernel where there is
>> no limit on the maximum frequency.

Thanks for that explanation. It makes perfect sense.
I take it the same must be true for dev.rtc.max-user-freq as well.

BTW. Do you know the unit of these values?
  cat /sys/class/rtc/rtc0/max_user_freq
  cat /proc/sys/dev/hpet/max-user-freq
are they Hz?

linux-2.6/Documentation/hpet.txt does not mention it at all and
linux-2.6/Documentation/rtc.txt hints it's Hz but does not explicitly
say so.

>> Regards,
>> Clemens
> 
> IIRC someone on jack-devel mailing list had issues when using mplayer
> with the value 64 and it was solved when using the value 1024. But as I
> mentioned before, for my USB MIDI there was a difference between system
> timer and hr timer, but there was no difference for the value 64 and
> 1024, when using hr timer.
> 
> Btw. I don't understand what a maximum frequency in the context does
> mean. If 64 or 1024 should have impact, what would be the result?
> 
> System timer for a kernel-rt is set up to 1000Hz and hr timer is at
> 1000000000Hz.
> 
> What is 'max-user-freq' for?

It limits the maximum frequency at which user-space applications can
[request to] receive "wakeup calls" from the hr-timer.

see also the "Timers" thread on LAD last November:
http://linuxaudio.org/mailarchive/lad/2009/11/7/161647

> Cheers!
> 
> Ralf
> 
> 
best,
robin

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