Re: [LAU] rtirq

On Fri, 20 Mar 2015, Joakim Hernberg wrote:

> with jitter. Further, at least on windows the midi isn't handled at all
> by the ASIO driver, so I doubt that the ASIO buffer size would have any
> impact at all on midi timing. I think this is different on linux using
> jack midi, but i suspect that the alsa sequencer won't be tied at all
> to any buffer size that JACK uses. I might be wrong about this though?

The alsa sequencer gets it's timing from the OS, It seems to say from the
wall clock, but is in fractions of a second from when the alsa sequencer
is started. Raw MIDI is just as soon as it comes in... but I am not sure
what buffering there is or not. I would think that the buffer should be
cleared each and every time any byte comes in. That would be the only way
single byte midi rt commands could be real time. I do not see irq that
belongs to my midi port (mpu401 clone), but it may be called from the
ensoniq driver.

I do not know how jack gets it's date stamp for a midi event ( or if that
time is at the first or last byte of an event... jack deals with midi
events) I would assume if it is using alsa-seq, it uses the time stamp
from there. With raw I don't know. From Paul's comment, I would guess the
sample at the end of the last buffer input plus time to calc current
sample time stamp.

jack1 uses ajmidid internally, and ajmidid is recommended forjack2 as
well. I don't have a clue how time stamp is created with this.

I think with firewire, the time stamp is a part of the transport... but it
has been a while since I looked at it.

--
Len Ovens
www.ovenwerks.net
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