Re: [alsa-devel] OSX Core Audio ASYNC OUT with rate feedback format ?

30 Sep 2010


      Alex <lee188 <at> singnet.com.sg> writes:
...
Hi Daniel et al,
I have successfully interfaced the sdr-widget with Linux alsa-driver
 for ASYNC 
OUT with rate feedback.  Found out after much trial
 and error and reading of the 
usbaudio alsa-driver source code that you are
 using 12.13 as the format for the 
feedback rate !!!  I was trying with 10.14 (UAC1 v1.2 specs
, I think) in 3 bytes, 
and 16.16 (USB 2.0) in 4 bytes for quite a number of days
 with no success !!!
However, 12.13 in 4 bytes, whilst working like a charm
 with Linux, does NOT work 
with OSX.
Would you know the format used by OSX?
Thanks.
Alex
Hi Daniel et al,
This is an excerpt from:
http://www.opensource.apple.com/source/AppleUSBAudio/AppleUSBAudio-
273.4.1/AppleUSBAudioStream.cpp
==============================================================
    associatedEndpoint.type = kUSBIsoc;
    associatedEndpoint.direction = kUSBIn;
    // The associated endpoint always goes "in"
    // The sample rate should be either
 a 3-byte 10.14 or a 4-byte 16.16
    associatedEndpoint.maxPacketSize = mFeedbackPacketSize;
    associatedEndpoint.interval = 0xFF;
    mAssociatedPipe = mStreamInterface->FindNextPipe (NULL, 
&associatedEndpoint);
    FailWithAction (NULL == mAssociatedPipe, result = 
kIOReturnError, Exit);
===============================================================
Alex