coreaudio usb driver
coreaudio usb driver
- Subject: coreaudio usb driver
- From: Eugene Gavrilov <email@hidden>
- Date: Mon, 1 Dec 2008 23:10:04 +0300
Hello,
I'm developing a driver for Mac OS X for USB 2.0 and 1.1 devices
(which are not class-compliant).
I noticed that sometimes IOAudioEngine::clipOutputSamples() function
sends a request with 'numSampleFrames' = 0. Is this correct? Why can
this happen? Can this influence driver performance or indicate any
problems with the timestamps? I'm also getting resetClipPosition()
notification - but I don't know whether I need to deal with it or not.
Original "Apple USB Audio Driver" has a set of very complicated
timestamp calculation algorithms with separate anchored time stamp
timers and jitter filters.. Is there a way to implement it in a less-
complex way?
My audio driver works quite fine, even with very small buffer sizes
(32, 64 samples), but I'm experiencing problems with certain 3-rd
party software, such as 'Cubase LE': there are occasional clicks and
"click storms", especially right after sampling rate change - and in
some cases the application can not recover automatically - even after
a number of manual resets. (But my driver + Apple aggregated driver +
Cubase work fine, without problems).
I suspect the problem is with synchronous start-up of the two audio
engines (playback and recording), as they are implemented independent
in my driver (similar to Apple USB Audio Driver), but I don't know
where to dig into..
Is there a way to check the timestamps calculated by the driver? I
tried "HALLab" application, but it does not show any problems with the
timestamps: they seem to be reported accurately, "Late" field is
always less than 0.1 ms. Is there any documentation on HALLab available?
I would appreciate any help on this topic, thank you in advance!
Regards,
Eugene Gavrilov
Senior Software Engineer,
CEntrance, Inc.
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